Engine
Q: Any aftermarket air-intake upgrades available?
A: Arizona Speed and Marine makes a nice system:
Evergreen Performance recently released a kit that is very similar to the AS&M kit. The main differences are that it is a ceramic coated steel instead of chrome, so the air charge supposedly stays somewhat cooler. Also, the air filter is angled so that the fit problems that occur with the AS&M and Callaway kits are remedied. As an added bonus, it is only about $250 for NAISSO members ($300 to noinmembers), which is at least $50 cheaper than either of the other two kits.
There is also a system available from Callaway, known as the "Honker". It is a cold air system. You remove the old filter box and all resonators, reposition the computer up and aft on the fender, and drill a 3 5/8" hole straight down where the computer was. There's a big cavity below this hole that is covered on the bottom with a large (stock) hunk of plastic. The fit problem is that the hole and tube that passed through it ends up being too far aft to allow the filter to fit comfortably with the lower plastic piece that bolts up from the bottom. It can be forced, though. The unit is $295 (P/N: C9701) direct from Callaway Cars (Phone (203)-434-9002, located at 3 High Street, Old Lyme, CT 06371).
Illusions Motorsports has recently announced their cowl induction hood for the Impala. It offers true cold air induction from the high-pressure cowl area. The intake itself is polished stainless steel with a custom built airbox and K&N filter. The hood is a one-piece fiberglass unit with a decent sized scoop on it. The hood goes for $600, while the induction kit is $400. The order line is 1-800-775-2811 and the tech line is (713) 370-6062.
Several other companies are now getting into the fray, such as Hennessey, that just replace the rectangular baffle at the front of the engine and put a conical K&N on the end of the MAF. Normally, for the money, you get a better constructed unit. Higher priced units are metal where the cheaper ones are plastic. No real performance differences between them, unless you get one that draws in cool air (via a scoop or filter relocation) instead of underhood air.
Random Technology has also recently introduced a "ram air" system that mounts in the air dam below the radiator. The lower part of the system (spoiler, ram air box, duct work to air filter box) is pretty nice. Everything goes together well. The filter box bolts right to the cooling fan supports using already existing holes. The air filter box looks a little cheap (not the nice ABS plastic the factory unit is constructed of) and the duct work to the throttle body is squeezed into an oval shape and clamped to the throttle body with the factory clamp. There are several points where the plastic duct is stretched, making a potential location for a future tear as things age. A piece of bent stainless (or aluminum) pipe would replace most of the duct hose and mate to a WS6 T/A duct to the throttle body nicely, though. You MUST use the K&N filter with the filter box they use. The factory filter will not work.
ESP Motorsports, a longtime friend of NAISSO and the Impala in general, has a nice system. Instead of the traditional Camaro 1LE elbow or plugged Impala elbow, ESP takes a unique approach. They supply a Corvette Throttle Body Adapter, which does not turn as the elbow does; it goes straight forward and adapts the oval throttle body opening to a circular 3-1/2" opening. This piece eliminates the "Home Plate" baffle. It includes a MAT sensor and has an opening for the distributor vacuum hose. Next comes a mandrel bent 3-1/2" aluminum air plenum. This part connects to the throtle body adapter then makes a smooth 90 degree turn toward the MAF sensor. It has a wrinkle finsh black powder coating and looks like it came from the factory. This piece eliminates the 1st base/pitcher's mound baffle. At the far end of this is a stainless steel and rubber coupler for attaching the plenum tube to the MAF sensor. On the other side of the MAF, a 9" K&N cone filter is attached, replacing the factory air box, and a small clamp on K&N filter for the AIR pump. This piece does not poke through the LH fender; it sits where the factory air box was. Also worthy to note is the folks at ESP are wonderful to deal with.
The folks at SLP have also come up with a nice system. It is basically like the others, but stands out since it has two tiny K&N filters on the end instead of one large one.
The members of the Impala list have devised several inexpensive and very effective modifications to the stock intake system that are documented in the technical archives. For a maximum of $50 (or as little as $10), you can make an air intake system that flow as well as any aftermarket system that does not pull in cold air. This method has been dyno tested to provide about 10 real-world, not advertisement-generated, horsepower.
Note that GM manufactures as mass-air extension cable that you can use with custom air intakes. Part Number for Pontiac WS6 MAF extension is GM# 12529241, cost is $26.00
Several people have asked about the effectiveness of removing the honeycomb screen from before the MAF sensor. This screen is there to straighten airflow over the MAF so that it will provide consistent, truer readings. Removing it may result in a bit of a performance increase due to A) the lower restriction in the intake tract or B) the different reading that the MAF is getting helps to correct an already existing A/F ratio problem. Taking it out may cause a rough or erratic idle, and if the MAF sensor is accidentally damaged, it is an expensive part to replace. Also, you may have problems with emissions as the calibration for the stock MAF arrangement would be invalidated. It would probably be a more significant increase on a supercharged car that needs all of the airflow it can get.
Q: Will an aftermarket "air foil" increase performance?
A: Maybe, but not nearly as much as they advertise. At their absolute best, expect to see about 5HP gain, but possibly none. It's one of the "it can't hurt" mods: it may get you that extra .05 that you're looking for. There are really no ill effects, other than the $50 that you'll be losing from your wallet. It's purpose is to smooth and direct the air into the throttle body, which presents a flat face to the incoming air. The airfoil splits and directs it to the twin butterflys on the throttle body.
Q: During the 1-2 shift, there's a nasty squeal that comes from the engine, particularly during hard acceleration. I think it's the belt. What can I do about it?
A: This is a fairly common problem with LT1's making a lot of HP (or even some stock LT1s). Remove the old belt by using a box end wrench to loosen the idler pulley: it is either 1/2" (my car, from experience) or 9/16" (from the Helms manual). You don't actually loosen anything, the pulley is spring loaded and will take tension off of the belt. Then clean each of the pulleys using alcohol or brake parts cleaner. Make sure you don't use something that will leave a residue. Cotton swabs or a toothbrush work well for getting in the grooves on the pulleys. Next, you might want to use some fine grit sandpaper across the pulleys perpendicular to their rotation to rough up the surface just a little bit. Reclean with the brake parts cleaner to remove any sanding gunk. Next, install a brand new belt, routing it in the same manner as the one you took off. A couple shots of belt dressing will finish the job. When cleaning, make sure you do the power steering pump well: that seems to be where the slippage takes place.
Q: I've heard that the camshaft on the Impala was toned down. Is that true?
A: Here's the specs:
Valve Lift Valve Lift Valve Lift
Lobe Lift 1.5 Rocker 1.6 Rocker 1.7 Rocker
Application Int. Exh. Int. Exh. Int. Exh. Int. Exh.
====================================================================
'94-'95 B/D-car LT1 0.279 0.287 0.418 0.430 0.446 0.459 0.474 0.487
'96 B/D-car LT1 0.276 0.285 0.414 0.428 0.442 0.457 0.469 0.485
--------------------------------------------------------------------
'92-'93 F/Y-car LT1 0.300 0.300 0.450 0.450 0.480 0.480 0.510 0.510
'94-'95 F/Y-car LT1 0.300 0.307 0.450 0.460 0.480 0.491 0.510 0.521
'96 F/Y-car LT1 0.298 0.306 0.447 0.459 0.477 0.490 0.507 0.520
--------------------------------------------------------------------
'96 Y-car LT4 0.298 0.299 0.446 0.449 0.476 0.479 0.506 0.509
--------------------------------------------------------------------
GMSPO ZZ3 HO Cam 0.316 0.340 0.474 0.510 0.506 0.544 0.537 0.578
GMSPO LT4 HO Cam 0.328 0.328 0.492 0.492 0.525 0.525 0.558 0.558
====================================================================
B F/Y LT4 TPIS
Cam LT1 LT1 LT4 ZZ3 HOT ZZ9
=====================================================
Intake Lift .418 .447 .476 .474 .525 .484
Duration --- 205 203 208 218 212
lobe Centerline --- 117 115 109 --- ---
-----------------------------------------------------
Exhaust Lift .430 .459 .480 .510 .525 .520
Duration --- 207 210 221 228 226
Lobe Centerline --- 117 115 115 --- ---
-----------------------------------------------------
Lobe Separation --- 117 115 112 --- 112
All durations are reported at .050 lift. The LT1 cam duration specs are from an article in '92 and at that time the lift was .450 for both intake and exhaust. I don't know if the duration specs have changed since then, but I don't think they have. Note that the LT1, ZZ3 and TPIS ZZ9 cams are with 1.5 rockers, with the LT4's 1.6 rockers the lift works out to the following:
LT4
LT1 LT1 LT4 ZZ3 ZZ3 HOT ZZ9 ZZ9
Cam/Rocker 1.5 1.6 1.6 1.5 1.6 1.6 1.5 1.6
-------------------------------------------------------
Intake Lift .450 .480 .476 .474 .506 .525 .484 .516
Exhaust Lift .460 .490 .480 .510 .544 .525 .420 .555
The ZZ3 cam is from a smog-legal crate motor that Chevy sells as an upgrade in the '85-'87 F-cars. It is a street cams that will produce good vacuum and run with a stock converter. Installation in a Corvette LT1 resulted in a 30 HP peak gain, with more HP and Torque everywhere in the rpm range! The cam (P/N 10185071, cost $173.58) could be worth even more power compared to the cam used in the B-cars.
There are two versions of LT1 with respect to the camshaft, water pump, and distributor drive system. These parts are not interchangeable between the 1st and 2nd designs. The 2nd design camshaft features a slightly modified drive end with a larger pilot hole and a longer pin for the drive mechanism. The 2nd design water pump is modified for the new drive, and the 2nd design distributor has a modified drive and a moisture ventilation system that taps into the air intake duct. The ventilation system was added because the low mounted distributor tended to pick up moisture, causing it to misfire. '94 and up B-cars have the second design, and all other LT1's got it in '95.
The ZZ3 cam uses the 1st design, which is the same cam as on most Chevy smallblocks. Fortunately the pilot hole can easily be machined to the larger size and a longer pin installed by any competent machine shop in about 15 minutes. This modification would have to be done to the cam to be used in a 2nd design application, or you could change the water pump and distributor back to the 1st design type (not recommended!).
Myron Cottrell, President of Tuned Port Injection Specialties (TPIS) suggests the ZZ-9 cam with the 700-132 springs. He indicated that this combination would work well with the stock iron heads and would not require any machining, and that this cam on a stock aluminum headed LT1 produces 60 plus horsepower. He estimates at least 40 horsepower on the iron headed impala. The cam is $375 and the springs are $126. He also indicated that these springs would work with 1.6 roller rockers. He has found better HP numbers by staggering 1.6 roller rockers on the intake and 1.5 rollers on the exhaust. The duration of the ZZ-9 is 211 intake and 226 exhaust at .050. The lift is .485 intake and .525 exhaust with lobe separation being 112 degrees.
Another interesting way to compare camshafts is to compare the engines corrected compression ratio:
The effective stroke can be use to calculate the effective compression ratio which is an indicator of low rpm torque.
After you draw this picture you can work out the equation for it. Assuming the intake closes between 0 and 90 degrees ABDC:
Effective Compression Ratio = CRe
Combustion chamber volume =
V
Effective stroke = Se
Cylinder bore = B
Crankshaft Stroke =
Sc
Valve Closing Angle ABDC = A
Rod Length = R
Se = R + Sc/2 - (R^2-(sin(A)Sc/2)^2)^.5 + cos(A)Sc/2
Should compare to the graphic answer above.
CRe = ((Se * Pi(B)^2/4) + V)/V
This is (Effective stroke X bore area + Combustion chamber volume) / Combustion chamber volume
As you may know, any aftermarket cam needs to have a dowel installed in it for the distributor on the LT1. Here is the information you will need to have the machine shop take care of that:
- -
-------------/ - |
/ |A |B
\ | |
-------------\ - |
- -
|-|
C
|---------------|
D
The approximate dimensions are as follows:
A = 12mm
B = 17mm
C = 3mm
D = 26mm
The hole just has to be large and deep enough to clear the distributor pilot shaft. Converting the metric measurements to english basically says we have about a 1/2" diameter hole (A) that is about 1" deep (D). There is a chamfer on the entrance to the hole about 1/8" deep (C) that extends it to about 11/16" in diameter (B). I'm not sure if the chamfer is important at all, but that's what it is on a stock cam.
There is already an existing pilot hole in the older design cams like the ZZ3, but it is not as large in diameter nor as deep. Any machine shop should be able to enlarge (drill out) this hole easily.
The newer design LT1/LT4 cams also use a longer dowel pin in a hole to the side of the pilot hole. The new dowel pin is the same diameter as the older one, it is just longer. The new pin protrudes 14mm or about 9/16" out from the end of the cam. This new design pin is available from GM under part number 10214485 (cost $0.92). It is a simple matter to pull out the existing (shorter) pin and tap in the longer one.
Q: Are there any "chips" that I can swap in for better performance?
A: There have been several factory updates. Unfortunately, it appears that the first may have a desirable "second gear start" function that the second and third seem to lose.
The Impala (and all LT1 equipped cars) no longer have removable EPROMs that are simply swapped out. Instead, the PCM contains an EEPROM that can be reprogramed from the diagnostic port. If you want to replace your PCM or get a spare when you send it away to be reprogrammed, there are only certain LT1 PCM's that will work. The 94-95 Vette PCM is different than the Impala/Z28 PCM. The number to get for the 94-95 Impala is P/N 16188051. This is used only on the LT1 and the L99, so it can be out of any 94-95 Caprice, Impala, Roadmaster, Fleetwood, Trans-Am, Formula, Z28, or B4C Camaro. For 1996, all L99, LT1, and LT4 engines use the same PCM. This is P/N 16214399.
There are several devices that allow modification of the stock PCM program:
The HyperTech is a true PCM reprogrammer that will download the stock PCM program into itself, modify it, and rewrite the flash ROM in the PCM with the modified program. It also keeps a copy of your stock PCM program so you can return the vehicle to completely stock setup in minutes. Supposedly, the Power Programmer Plus is due to be released soon, which allows user modification of all of the parameters under PCM control (shift firmness, shift points, fan temps, gear changes, etc.), as well as allowing different chips to be plugged into it. You will no longer need to buy a programmer: you can use someone elses and just buy a chip. Also, this tool will have the capability of being used as a scan tool, much like the GM Tech 1 scanner.
Program Features
The new Hypertech Power Programmer Plus is now just coming into production. It corrects for virtually any gear ratio available up to 4.10, tire diameters from 24"-30" for speedo corrections, shift firmness at all throttle positions, fan temperatures, and adjustable WOT shift points. The PPP comes with a very detailed manual for ease of use and takes about 7 1/2 minutes to load. The engine tuning is similar to the original Power Programmer. Members have reported a .3 second gain in the 1/4 with the new programmer over the old one. However, several users have reported problems with Hypertechs calibration for different rear gears.
SuperChips will reprogram your PCM for you in much the same way GM does. However, you must ship the PCM to them (causing downtime for your car) or drive to one of their authorized reprogramming facilities. SuperChips will also dyno-tune your car to make the most power with your current mods. Recently, SuperChips has performed dyno testing on all of the current chips out there, and have constructed a new chip which has greater power gains than any of them. This chip will be sold for about
Program Features
Jones Electronic Technologies (JET)
The JET device does not really modify the PCM program in the car. Instead, it works by intercepting the sensor signals and modifying it so the PCM outputs will be modified. JET industries claims that this was necessary to get outside the "walls" created by the stock PCM.
Program Features
"Z" Industries
The "Z" Industries chip Program Features
Q: There's a lot of ticking/clattering coming from the valvetrain. Is this normal?
A: For the Impala, it is normal. The increased noise is due to the metal valvecovers used instead of the thick plastic ones on the Corvette. The LT1 is bad in this respect.
A TSB has been issued that covers some of these noises. Contact your dealer if you are concerned. The TSB follows:
Chevrolet 67-61-14
Issued 04/18/96
Models: 1994-96 Buick Roadmaster
1994-96 Cadillac Fleetwood
1994-96
Chevrolet Caprice, Impala SS
With 4.3Lm 5.7L V8 Engine (Vins w, p - RPOS L99,
LT1)
Subject: Engine Noise (Install Valve Stem Oil Seal)
Condition: A rhythmic engine noise at idle. The noise, which occurs at half engine speed, has been described as a "whoop whoop" (similar to a helicopter idling), and engine rattle noise (not to be confused with pvc rattle), a lifter tick in the lower end, a balance shaft noise, or a rod knock. When using a stethoscope, the noise will sound as coming from deep within the engine. The noise may be heard in the passenger compartment and in s/t vehicles is audible at the catalytic converter and tail pipe.
Important: The noise will get louder as the engine warms up at idle. The noise does not diminish with removal of the accessory drive belt, balance shaft gear, or disconnecting the torque converter.
Cause: The noise may be caused by a low level of lubrication on the exhaust valve stem, creating a "slip-stick" condition between the valve stem and the vlave guide.
Correction: Install the valve stem oil seal listed below, on the exhaust valve guides only. Lightly lubricate the seal, and with finger pressure only, push it on to the valve stem and down on to the exhaust valve guide. Important: Do not install this seal on the intake valve guides. The seal is not released for intake vlave application in the above indentified vehicles.
New rocker cover gaskets may be required.
Parts are available from GMSPO as follows: LT1 oil seal, 8, P/N 460483
Iron Head Rocker cover, 2, P/N 10046089
Q: I found a connector with no mate on my car today. Did something fall off, or was never installed from the factory?
A: Probably not. The wiring harness for the engine is the same for the Chevy's, Buick's, and Caddy's, so there are some unused connectors that are simply hanging there in the Chevy. The most famous is a little blue connector near the hood latch brace. This is for the outside temperature sensor for the Buick's automatic climate control.
Q: What are the major differences btween the LT1 in the Camaro and the Impala LT1? How about the LT4?
A:
| Item/Description | F/Y-Car | B-car |
|---|---|---|
| Block mains: | 4-bolt (Y-Car) | 2-bolt |
| Heads: | Aluminum | Cast-iron |
| Cam lift specs: | .450/.460 (int/exh) | .417/.429 (int/exh) |
| Valve springs: | 268 lb/in | 393 lb/in |
| Valve spring od. | 1.300" | 1.241" |
| Valve spring inst ht: | 1.78" | 1.70" |
| MAF id: | 3.5" | 3.25" |
In the F-body applications, the alloy heads have larger intake ports giving lower port velocities meaning they have a tendency to produce lower torque at the bottom end. They also have different exhaust ports ("D" shaped) which flow better, producing more power throughout the range. Aluminum conducts heat much better which reduces the tendency to get for ping-inducing hot spots, allowing higher compression. The iron heads are much more resistant to warping from heat, though, and the valve size and design are optimized for torque. Several engine builders have found that porting stock iron heads on an Impala produces better results than bolting on the aluminum heads.
As for differences between the LT4 and the LT1:
Q: My Impala has intermittent electrical problems (flickering instruments or lights, engine hesitation or stalling), or the cover to the auxiliary battery connection has melted (near the underhood electrical center). What's up?
A: Under certain conditions, the battery cable connection at the underhood electrical center stud may overheat. This may cause melting of the plastic batter cable cover, the plastic stud housing, or the stud itself, resulting in intermittent loss of vehicle power. This is more likely to occur if extra electrical loads are added to the car. The fix involves moving the terminal, and is coverd in TSB 43-81-48.
Q: What can I do improve the looks of the engine compartment or at least open up the stock air intake path up a little?
A: There are several area to address:
As for the stock air box, several list members have cut additional holes in it underneath the air filter. This, along with a K&N filter, allows the engine to breath a lot better than the small, stock, inlet does. You might also want to consider one of the aftermarket intakes available for more flow improvements. Another option is to connect a conical K&N filter to the end of the MAF and leave the top of the airbox off for a replacable, free-breathing system. See the air box modification instructions in the technical area for details on doing this.
The square baffle between the MAF should be removed. It just limits full throttle noise, and for most of us, this isn't a concern. It also introduces turbulance in the intake stream, which robs power, and is a concern for us. The simplest solution is to replace it with a straight piece of pipe (PVC, chromed, or stainless), or you could also route a 3" hose right through the square baffle to preserve the "stock" look and get the same benefits. The aftermarket intakes usually eliminate this baffle as well as the stock air box. Check the section on removing the rectangular baffle in the technical archives for details on this operation.
The intake elbow and the "home plate" baffle on top of the engine are interrelated. Unlike other LT1 intakes, the Impala elbow has a hole in the top of it that connects to this plate. If you are removing the top baffle, you must either plug this hole or replace the elbow. You can plug the hole by inserting something (a paint can top w/ duct tape, a plumbing test plug, a Nestea cap, a hockey puck, a water heater tee cap, and others have been suggested and used) into the hole on the bottom of the baffle. The duct in the top of the elbow is then closed off. You can also replace the stock elbow with one from a 94-96 1LE f-car. This is documented in the home plate removal section of the technical archives.
As for flow, the stock paper element flows around 200CFM, the K&N replacement for the stock element flows around 410CFM, and the conical filter replacement will flow up to 900 CFM. At peak volumetric efficiency of the intake, the LT1 will ingest around 530CFM at 5500RPM. This can be calculated using the formula cfm = (cid * rpm * Ve)/(3,456).
Here, Ve = volumetric efficiency. That is basically how well your car sucks. CC said a typical street car has a Ve of around 0.85, whereas a racer can be 1.0 or higher (how higher, I don't know). If we figure 0.85 for the Impala, this revises the peak figure down to 473 cfm at redline.
As for other mods, you can install the Corvette fuel injector covers and plastic valve covers. This totally changes the apearance of the engine and makes it look like a Corvette LT1. You can also add red Chevrolet "SS" emblems on the fuel injector covers which come originally on the doors of '95 Chevy S-10 "SS" model pickups. These emblems could also be used on the elbow caps, as referenced above. Check out the Corvette engine dress section of the technical archives for more information.
Q: Can I keep my engine cooler by modifying the fans?
A: You could install an aftermarket PCM program that changes the temperature where they are supposed to come on. This will be in effect all of the time. JET also makes a kit that will turn the fans on at a cooler temperature: it wires into the stock harness.
Alternatively, you could install a factory thermostatic switch in a pre-existing (plugged) water jacket hole in the LH cylinder head, and then wire it through a hidden toggle switch (mounted in the under-hood relay box) to allow you to turn on the high and low speed fan relays automatically at 203 degrees or manually. The thermostatic switch is wired in parallel with the standard fan relay circuit so the PCM can still control the fans as normal. BTW, the thermostatic switch is the same one installed in the intake manifold as the high speed fan switch in the GN and TTA.
There are two sources for the thermostatic switch. There is the factory GM unit, and a company called GMP Parts Co. (916-685-1055) manufactures an improved version. If you want the improved design switch, call GMP, ask for John Flagg and tell him Scott Mueller sent you. The GM switch is available under P/N 3053190 and costs around $20. This switch has a 3/8 pipe thread, and there are 3/8 pipe plugged holes in the LT1 cylinder heads that are just perfect for installing this switch.
As for other modifications to help your LT1 "keep its cool", replace the factory thermostat with a 160 degree unit. These are available from many of the LT1 aftermarket vendors. Removing home plate also allow the engine to cool off faster, and allows you to lay bags of ice on the intake for engine cooling at the drag strip.
Q: Will an adjustable fuel pressure regulator help my car?
A: The PCM controls the air / fuel ration using the O2 sensor at just about all RPMs except WOT. Any increases in the fuel pressure at this point will just result in shorter pulse widths and probably worse performance. At WOT, an adjustable regulator may buy some extra power if you have done other modifications to the engine, such as an aftermarket air intake and an aftermarket exhaust system . I don't think anyone on the list currently runs with an adjustable regulator. An adjustable regulator could also be useful at the track to tune for environmental conditions or altitude. However, several magazine reviews have found that there is a very narrow window (+/- .5 PSI) where the LT1 begins to lose power rapidly, and they only gained a couple of HP in the best cases.
Q: How do the heads compare between the Impala SS LT1, F-Body LT1, Corvette LT1, and the Corvette LT4? A: The Corvette and F-Body LT1 heads are identical aluminum units, while the Impala version is iron. The LT4 heads are completely different. Here's how they compare on several critical areas:
This will probably run $400-$500 for all of the parts and work needed, and does not include any performance porting yet. All of this should be OK on either set of the aluminum heads. So, if you plan to upgrade the camshaft or rockers, the aluminum heads might be a good investment for just a little bit more than machining the stock iron heads.
Q: What's the deal with the green hoses on the Police Package Caprices?
A: This is option 1T1: "Hose, Radiator and Heater, Silicone Rubber (SEO)". These are green silicone radiator and heater hoses that directly replace the factory hoses. They replace all of the black rubber hoses between the radiator, engine, heater core, overflow tank, and thermostat housing. These hoses are made from 100% pure silicone rubber and will last the entire life of the vehicle, they never need to be replaced. They are installed with 100% stainless steel (including the screw) worm gear clamps (as used in the factory Police package) instead of the standard squeeze clamps for additional durability and reliability.
Q: I used a engine monitoring tool (e.g. Diacom, Auto-Xray, or Tech 1) on my engine and see retard as I floor it, no matter what octane I use. Is there something wrong with my engine?
A: Probably not: it could be because of emissions. Many cars retard the timing on take-off (slightly retard and *then* advance) to reduce the emissions. If you have a scan tool that can handle it, check the parameter "KNOCK SENSOR" in the PCM. It's a numeric counter that records the number of knocks that the knock sensor has detected. If you have the capability of data capture on your tool, do a run and look at the KNOCK SENSOR parameter over the time course of a perceived knock condition. That should tell you if the retard is actually due to "real knocks" or some other reason. If it increased, your knocking. If not, you have something else going on. BTW, the parameter "KNOCK RETARD" will tell you how many degrees off of the optimum timing the PCM has retarded your timing to counteract a detected knock condition.
If you know that your knock sensor is firing off without the engine knocking, then you can "desensitize" it electronically. NAISSO member Steve Chapple ("Rocket") came up with the following scheme.
I measured the knock sensor circuit (2 sensors wired in parallel to ground, see diagram below) at the dark blue wire at the PCM to be around 1925 ohms. This is consistent with Mike Chaney's measurement of 3850 ohms for the F-body's one sensor. 3850 in parallel with 3850 is 1925 ohms (R1*R2/R1+R2). Our Impala most likely uses the same knock sensor, we have two vs. one on the F-body.
Original Circuit:
_________
____________ dk blue wire | |
--|||---------|knock sensor|---|-----------------------------| PCM |
ground ------------ | D22 | |
____________ | blue ---------
--|||---------|knock sensor|---| connector
ground ------------
To desensitize the sensor circuit you can add a resistor network between
the PCM and the knock sensors (see circuit below). You simply cut the dark blue
wire (D22) in the "blue" connector bundle a few inches from the PCM and place
the following circuit in line. R1 goes to ground (screw on the PCM) and R2 goes
in series before the PCM.
Desensitized Circuit:
+------+
dark blue wire cut cut | |
<---------------------/ / /---|----------/\/\/\/------/ / / --------| PCM |
to knock sensors | R2 D22 | |
| | |
| dark +------+
> blue wire
< R1
>
|
|
__|__
- Ground
Ah...the resistor values, yes we need that. I calculated values for a 25%
reduction and 33% reduction. I have the formulas below if you want something
more or less.
33% reduction: R1 = 3856 ohms, R2 = 641 ohms
25% reduction: R1 = 5779
ohms, R2 = 481 ohms
Formulas:
R3 = (1-X) * Rk, where X is the desired reduction (i.e. X= .25 for 25% or .33
for 33%)
Rk = 1925 ohms which is the measured resistance of the knock sensors
at the blue wire
R2 = Rk-R3
After a little algebra:
R1 = Rk*R3/Rk-R3
You may not be able to find the exact resistor values. You can build them by adding smaller resistors together.
In the DC (no knock) state, the PCM still sees the 1925 ohms resistance. Under a knock condition, the knock sensor will send a voltage to the PCM which will be attenuated by the series resistor R2. R1 really has no attenuating effect.
This idea worked for Mike Chaney's '95 Trans AM. He had a stumble at around 5000 RPM that he thought was being caused by false knock. His 25% reduction circuit cured the problem.
Note that the circuit as shown will only apply to the 94 - 95 cars. They use the 10456126 knock sensor, which has a 4K ohm internal resistor. The 96 switched to the 10456017 knock sensor, which has a 100K ohm internal resistor. The circuit would have to be revamped accordingly to compensate for the difference in sensors on the 96.
Q: What would it take to swap an LT4 into an Impala?
A: Not much! Some members have already even done this. The LT4 crate engine options can be summarized as follows:
LT4 '96 Corvette Production Engine - p/n 12551183, $5,950 list, $4,462.50 dealer cost. This is a complete '96 Corvette engine which includes everything from the oil pan to intake manifold with throttle body, fuel rail, fuel injectors, opti-spark distributor, ignition module and coil, spark plugs, and even wires. It also includes 'vette exhaust manifolds, water pump, harmonic balancer, accessory bracket, all engine sensors such as knock sensors, temperature sensors, oil psi and temperature sensors, and the throttle position sensor. It even includes $1,800 worth of (unnecessary) 'vette flywheel, magnesium bellhousing and clutch.
When installing this engine in an Impala, you will be removing the following parts and replacing them with the equivalent parts from the LT1 in the Impala or discarding them completely.
These are all NEW parts that come on the production LT4, and will be left over after the swap is complete. The magnesium bellhousing and clutch alone sell for $1,800 new, the injectors are over $600, throttle body is $450, exhaust manifolds are $275, and the water pump is $70. These items, along with the original LT1 from your Impala, can really help to subsidize the installation.
You also get many other notable items with the production engine including a new $450 distributor, $200 worth of red LT4 sparkplug wires, a $25 '96 higher energy ignition coil, new updated double platinum '96 sparkplugs, various new engine sensors, and even 6 qts of Mobil-1 oil and a PF-52 filter already installed.
Unfortunately the complete production engine will not be available much longer. There were only 300 extra LT4 engines left over after the '96 production run, and SLP took over 100 of them for the 100 '97 Camaro SSes they will be building with LT4 engines. The rest are the only ones left over for warranty and service exchange as well as over the counter sales.
To fill the gap once this engine is gone, GM Performance Parts has introduced a new LT4 Engine Kit, p/n 12371172. This is a 3/4 LT4 engine which is commonly referred to as a long block. This engine includes everything up to the heads, but is not a fully dressed production engine. It does not come with an intake manifold, fuel rail, injectors, throttle body, engine sensors, wiring, spark plugs, distributor, or exhaust manifolds. It does include a separate kit of parts with a 4bbl carbureted intake manifold, HEI distributor, Corvette water pump and harmonic balancer. Unfortunately all of these extra parts except the balancer are not needed in an LT1 swap situation and they will be left over. These parts are also not installed on the engine and do not include attaching hardware or gaskets.
You will need to purchase an LT4 intake manifold to complete the kit. The following parts will be left over from the LT4 Engine (3/4 engine) Kit:
Most everything else that is needed would be swapped over from the LT1 engine including the following items:
Theoretically the LT4 Engine Kit should be much more economical than the production engine due to less leftover parts, however if you can sell those leftover parts, it may shift the economy over to the production engine. I calculate roughly $3,200 worth of NEW parts will be leftover after the swap using the production engine, assuming you can get half price for them, that would mean a $1,600 rebate on the deal. Not to mention if you sell your original engine for $2,000 then the total cost of the LT4 swap is now only about $1,000 using the production engine!
As a side note, the paint code for the red LT4 intake color is GM70. The "universal code" WA-9075 is non-vendor specific and any shop supposedly can mix a WA paint code, so you may want to try that. Any GM shop should be able to get you the GM70. You may need to add a clear coat on top to get the correct effect.
Q: Will the Corvette "Mobil 1 Only" oil cap and plate fit on my Impala?
A: If you have a '94 or if you have switched to the Corvette valve covers, you can use the Corvette oil fill cap (P/N 12554955). Normal '95 and '96 cars can not use the cap due to a different oil fill neck. The plate/sticker can always be used, but the "best" mounting spot is where the first intake resonator rests on the radiator shroud, but other more creative mounting spots are also possible.
To construct a cap for the 95-96 models, or if you just want to use the new multi-colored cap from the C5 'Vettes, check out the technical archive on how to create one.
Q: Is there a nitrous oxide system available for the Impala?
Compucar makes a "wet" system for the LT1 which fogs fuel and nitrous through a plate that mounts in between the TB and the intake. From what I can gather, Compucar is a great company to deal with and they warranty every part of the system for life... no questions asked. The "supposed" weakness of this system is that the fuel may not make it back to the rear cylinders due the inadequacy of the fogging system and the design of the intake being optimized to flow air and not fuel. This bit of info comes mainly from the NOS guys trying to sell you their "dry" system (see below). The Compucar system is a 75/150HP system and can be purchased for around $600.
NOS makes a "dry" system that sprays nitrous thru the throttle body elbow into the intake. To get the added fuel, they increase fuel pressure with an added in-line fuel pump and decrease the return pressure to the fuel tank. This system is supposedly a bit more complicated to "tune". There is also questions about whether the injectors will work properly/effectively at the higher rate/pressures. From talking to people who have used the NOS and the Compucar, they say that the Compucar system is much better in pure quality of parts down to the brackets that hold the bottle in. NOS supposedly is not as flexible to deal with on parts/problems. NOS has 85% mkt share and are the current leader in Nitrous systems. The obvious risk of this system is that if you have a problem with fuel delivery on one of the cylinders, you have major problems! This is a 150HP system, part # is 05176, and jobber price is $675.00. It gives you everything you need for installation except the car and the guy/gal to do the work. You can use up to the 125 HP jetting without having to modify the internals of your Impala's engine. The jetting comes soft (rich) from the factory because of temperature differences around the country. If you were using the kit in hot weather all the time the jetting would be pretty close to perfect. If you use it in a moderate to cool environment you would be able to make more power by leaning out the fuel jet.
With any nitrous system you will need to retard timing. How much depends on whether you have aftermarket chips/prgmrs that advance your timing. The most flexible way I have discovered is to have something that retards your timing a specific number of degrees once the nitrous solonoid is activated. This can be done with products from MSD, etc. This lets you keep the performance advantages of your aftermarket chip/programmer while you are not on the bottle.
The million dollar question...."Will it harm my precious beast?" That one is tough to get a straight answer on. The NOS and Compucar guys say that with the 150HP kits (max. avail. for LT1) there is basically no risk in long term damage. But then they are in the business to sell systems. I would think that putting another 50% more of an explosion into your combustion chamber will have long term effects on pistons/rods/valves, etc. It all depends on how much you are "in it". From talking to people that have nitrous, it is VERY addictive and you will use it much more than you think. If you can stay out off the nitrous except at the track (don't forget about the tires you will go through) and want to have the "warm fuzzy feeling" of knowing you have low 13 sec power for that Saleen you may see in the right place at the right time, then go for it!
Q: What octane rating should I use in my Impala? Will I gain anything going with a higher octane?
A: Octane is added to gasoline to prevent knocking. If knock is detected in an Impala engine, the timing is automatically retarded to prevent any damage to the engine. However, retarding the timing also decreases the power that the engine puts out. Under normal circumstances, a stock Impala can run fine (i.e. no spark retard) on 87 octane gasoline. Factors such as heat, load, and gasoline quality affect the point at which the engine begins to knock. To ensure maximum performance, some owners run higher octane ratings to prevent any chance of knock.
Octane ratings have little effect on mileage, and the extra cost you pay at the pump would most assuredly negate any mileage gains you would experience from running a higher octane, anyway. Also, the same cleaners are put into each octane level, so don't believe the hype at the pump.
If you are using a performance PCM package, such as the Hypertech or SuperChips programs, then you probably need to use premium gasoline all the time. These programs are tuned for 92-93 octane to get the most power out of the engine (through advanced timing). The same thing goes for superchargers or nitrous applications.
Another data point to remember is the oxygenated gasoline (sold in some state year around and in others in the winter) contains less energy per gallon than conventional gasoline. Thus, power levels and mileage levels will be lower than with "normal" gasoline.
Q: Is there an oil cooler on the Impala?
A: Yes, there is. It is internal to the radiator. You could also special-install option 7P8: "Cooler, High Capacity Engine Oil". This is a heavy duty external oil-to-air aluminum plate cooler, similar to the external oil-to-air trans cooler, which is mounted on the LH side of the vehicle directly in front of the radiator. This cooler is standard on all Caprice police package vehicles, and replaces the oil-to-water cooler inside the LH radiator tank on civillian LT1 Caprices. It includes all aluminum pre-bent lines from the oil filter adapter and replaces the lighter duty oil-to-water cooler located in the LH radiator tank which is standard on the SS.
You'll need the following parts (net prices):
When you get your parts from the dealer, use the Cooler part # and have him screen print what the assembly looks like on the car. You should get a really nice parts explosion of all the parts and where they go.
Q: What is spark plug indexing, and what can it do for me?
A: Frank Halley writes:
Several companies sell "indexing washers" that allow you to change the orientation of the sparkplug tips relative to the head. Why you ask?
GM cut the threads for the 8 sparkplug holes in your car so they start at random angles. AC/Delco makes sparkplugs the same way. The threads on the plug are random, relative to the electrode construction. Therefore, some plug gaps point up, some down, and some sideways. However, the plugs are the most efficient when the gap faces "up" or toward the center of the combustion chamber. Otherwise the flame must travel around the electrode to get to the entire air/fuel mixture in the cylinder.
Indexing washers allow you to change how far the plugs go into the block. This allows you to change the orientation of the plug tips relative to the combustion chamber. Indexing is a good idea, but indexing washers have two drawbacks:
There is an alternative. I bought a new set of plugs, but you could use your old plugs for this as well. Measure where the plug threads start relative to the electrode. What you want is the angle from the electrode to where the thread starts when looking at the front of the plug. Write the amount down for each plug.
Using the plug nearest 000, measure the thread orientation in all eight cylinders. I did this by putting a piece of electrical tape on my sparkplug socket that corresponded to where the gap was on the plug. Write down the values, subtracting the value of the sparkplug thread orienation each time.
Now, match each cylinder with, the plug that comes the closest to the same angle you measured (put the 45 degree plug in the 45 degree cylinder). Check the first few with the tape on the plug socket to make sure you have the angles orientated correctly relative to each other.
I ran my car with this change and the plugs gapped at 0.055" today. There were no other changes to the car. It was the same track at about the same temperature. I was able to increase my average terminal speed in the 1/4 mile from 92.47 to 93.03, and the time from 15.031 seconds w/o to 14.905 seconds with. These figures indicate about a 5HP gain.
Q: What's the easy way to change spark plugs?
A: There is no easy way! Seriously, though, here are some suggestions from list members:
| Plug | Access | Tools | Difficulty |
|---|---|---|---|
| 1 | Top | Socket with Short Extension | Easy |
| 2 | Wheelwell | Socket with 10" 3/8 Extension | Very hard: remove the right front wheel, go through wheel well |
| 3 | Top | Socket with Short Extension | Easy |
| 4 | Wheelwell | Socket with 10" 3/8 Extension | Very hard: remove the right front wheel, go through wheel well |
| 5 | Top | Socket with Short Extension | Easy |
| 6 | Top | Socket with Short or No Extension | Moderate |
| 6 | Bottom | Socket with Short Extension | Moderate - watch out for cat and manifold |
| 8 | Top | Socket with Short or No Extension | Moderate |
Some other tips:
"Been there, Done that several times"!! Back to the index...
Q: Would underdrive, "power pulleys" free up some more power in the Impala?
A: In a word, no. The Impala has a 140amp alternator putting out 13.8 volts, which equates to a maximum output of 1932 watts, or 2.591 horsepower to run the alternator. So, accounting for ineffeciencies, your alternator is only pulling 3HP, at most (all accessories running). More often, it's more like 1.5HP, where a 1/3 underdrive pulley would save you only about .5HP. Actually, this is the best case for the pulleys: in fact, the alternator will put out current to match demand at RPM's above idle. This means that the only affect of the pulleys will be to reduce idle output from 75-100 amps to around 50 at idle. You would no longer be able to run all accessories at once without discharging the battery. In addition, there is more drain on the alternator once you start to run the motor because it has to recharge the drained battery.
Also, being that they are made out of soft aluminum, the belt will actually wear the pulleys over time, causing belt slippage, belt mis-alignment, inbalances, and other problems. This does not happen with the stock steel pulleys. If all you wanted was appearance, you should have the stock pulleys Jet Hot coated or perhaps powder coated or something. This would look good, and retain the proper charging at idle of the stock pulleys.
Q: What about using higher ratio rockers for the engine instead of the cam swap?
A: Crane offers self-aligning, 1.6:1 rockers that effectively increase the lift of the stock camshaft. There are no piston to valve clearance problems with these rockers. Several members of the list have used these and have had good results. Prices have been quoted from $275 to a bit over $300 for the parts. You can expect at least a 15HP gain with this modification. They have been found to be somewhat noisy in some installations, though. You should also get the K-Motion #0700 springs to complete the package, or you will probably get into valve float.
When installing the rockers on a stock cast iron head, be sure to check pushrod clearance as the steeper rockers alter the geometry slightly, and the pushrod clearance is tight. If you also upgrade to a higher lift or duration cam, you will probably need to get the heads machined to accept guideplates and screw studs. This will also allow you to use the standard, non-guided rockers. You should also get hardened pushrods from 94-95 LT1's (the 96's are non-hardened).
Q: Are there "scan tools" available for the LT1 that allow me to monitor the various engine parameters at work?
A: There are several. The best, by far, is the GM Tech 1 scan tool, which is used by the GM dealerships. However, at over $1000 a crack, this is out of the normal "mod" budget for most of us.
The next best solution is the Diacom by Rinda Technologies. Diacom is a package that will run on most laptops and can monitor and record most PCM activity for 94-95 cars. 96 support is currently incomplete, but most values are present. For more information, see their website at http://www.mcs.net/~rinda/auto.htm. The Auto-XRay is made by Jones Electronics. It is a stand-alone electronic device that can plug into the ALDL port on 94-95 Impalas. I am not sure if it works on 96s or not. Current best price is $??? from $??? (can someone help me here??? More info, please???). A NAISSO member is making a tool called the Scanmaster LT1 that is designed to display and record critical data from the PCM. The product is a small plastic box with the front panel being an LED readout. It just happens to fit in the hole that the junk tray sits in in the pull-out ashtray. It is also very easy to install since it only requires tapping into 12V+, a ground and the data wire that goes to the ALDL above your right knee.
In regular (closed loop) mode, the left side displays O2 sensor data and the right side displays the amount of spark timing retard. The fun begins when you step on the gas than one!) since the Scanmaster goes into record mode. What it records is the lowest O2 reading and the highest spark timing retard value along with both events' associated MPH (the reason for MPH rather than RPM is that the engine could see the same RPM at multiple vehicle speeds). This data is stored until the next time you step on the gas.
The extended mode is where you get to view the rest of the data:
Q: Is there a top-speed limiter on the Impala?
A: Yes, for 154 MPH, which is really a non-issue since it is drag-limited (in stock form) to about 140, anyway. Some '95s may have gotten the incorrect speed limiter due to the wrong tires getting put on the car. The dealer should fix this. Note that this speed occurs in overdrive, not third gear. Third is "only" good for 125 or so.
Q: The torque specs in the manual seem high for the thermostat housing. Are they correct?
A: NO!! Both the factory service manuals as well as the Hypertech documentation are INCORRECT with regards to the thermostat housing bolt torque. If you follow the incorrect specs (which are 3 times more torque than what is correct), you will either strip the threads out of the soft aluminum waterpump, or you will break the heads off of the tiny 5mm bolts! The manual states that they are supposed to take 21 ft-lbs of torque, which is far to high for the size and material of the bolts. The correct specification for torque on the thermostat housing bolts (as found in the '96 Y-car (Corvette) service manual) is 10 n/m or 89 in-lbs, which would be 7.42 ft-lbs.
Q: Is there a power steering cooler available?
A: Option 7L9: "Cooler, Power Steering Fluid (SEO)". This is a metal tube cooler that crosses the front of the vehicle from side to side directly under and behind the radiator. This is standard equipment on Caprice police package vehicles and is used to prevent the power steering fluid from overheating during spirited driving sessions.
You will need a Pipe Assembly (GM P/N 26036034) and 2 "Clamp-Lo" (GM P/N 2091638). The service manual details the installation of the lines. There's also a diagram of how to route the lines from the gear box to the power steering reservoir.
For those who like to use all OEM parts on their cars, there are also two more p/n's needed: #11509363 (10 pack of bolts), and #12337917 "Nut, RR BP" (essentially a clip with a nut on one side). These two other parts are required to correctly (as OEM) fasten the pipe assembly to the bottom of the radiator crossmember. The total cost for me for ALL of the parts for this mod is about $45.00.
Also be sure to pick up an additional 32oz of GM power steering fluid to compensate for the larger capacity, and also to use as part of the bleeding process.
Q: Are there supercharger kits available for the Impala?
A: There are several kits available, including the Vortech, the Paxton, and the ATI ProCharger. Apparently, the Vortech guys split off from Paxton when they wanted to make some changes to the design. The Vortech is their brainchild. The ATI unit includes an intercooler which allows them to produce higher boost than the Vortech or Paxton. The Vortech installation swaps in larger injectors, and a MAP sensor to run a booster fuel pump when additional fuel is required. They also report much higher gains in horsepower than the Paxton. The Vortech uses circulated engine oil rather than a separate resevoir that must be changed like the Paxton. Several F-car people have run 12s with no other mods, and tests indicate that the Vortech on an F-car LT1 is worth 113 more HP at the rear wheels. The only company that makes a Vortech kit specifically for the Impala is Specialty Vehicles International (SVI) in Colorado Springs, Colorado, (303) 329-8238 or (719) 573-0857. The rest of the kits are adaptions (some decent, some not) of the Camaro kit.
The Paxton unit includes the supercharger, three additional injectors to supply extra fuel to the engine while under boost, and the Paxta-Map boost timing manager. The Paxta-Map allows you to dial in more injector pulse width from the cockpit as a function of boost. This allows fine tuning of the amount of fuel delivered to the engine. The Paxton system also includes a method to retard the timing as the boost grows, like the Vortech.
The ATI system is relatively new, but they claim to have built racing superchargers for a long time and have had some Mustang products around. Their "hook" is the addition of an intercooler for the boost. The intercooler allows them to run much higher boost (up to 12 PSI on a mildly modified engine) without detonating. The Paxton and the Vortech used to be available in 8 or 6 PSI units, but the 8 PSI units are no longer available, supposedly due to engine problems. ATI claims their 9 PSI unit will work fine on a stock engine. Remember that these PSI figures are probably quoted at the output of the supercharger and not at the input to the engine: the intercooler costs a few PSI. There seems to be a difficulty in getting ProChargers tuned and running correctly on the Impalas. Also, there are no Impala- specific kits available yet.
Q: What's a throttle body heater, and why would I want to get rid of it? A: Engine coolant flow is provided to the throttle body to improve cold driveability. Engine coolant is routed from the rear of both cylinder heads to the throttle body and then to the coolant recovery reservoir."
If you determine that your car won't be driven in temperatures that would cause ice to form on the throttle body, you might consider disconnecting the heater. The heater's only function is to reduce the chance of ice forming on the throttle body. Without the heater, the intake air is cooler and the engine can make more HP.
To disconnect the heater, you will route the coolant line directly from the cylinder head to the coolant reservoir without going through the throttle body.
First, put something under the engine to catch any coolant that leaks out when reconnecting the hose. An oil change pan works very well for this. Get a rag to protect the opti-spark distributor from getting wet. Put it somewhere where you can reach it quickly.
There is a metal pipe running the length of the cylinder head on the passenger's side of the engine. It is attached to the bottom of the valve cover on the outside of the engine. There is a very short, 90 degree rubber elbow from the end of that pipe to a pipe on the throttle body. Two spring clamps hold the rubber elbow to the respective pipes. This hose is the most difficult to remove because of the spring clips.
On the driver's side of the throttle body, there is a rubber tube running from the throttle body to the coolant reservoir. It is held on with a screw-type hose clamp. This hose is very easy to remove.
You should loosen the hose from the driver's side of the throttle body first, but not remove it. If you remove it, coolant will leak out while you remove the other hose. With a screwdriver, loosen the clamp on the long hose. Get that spare rag and hold it under the hose while you momentarily remove it. By removing the hose now, when coolant isn't running all over the engine, you ensure that you can get it off quickly when you need to.
Now for the hard part. Stuff the rag under the short hose to catch most of the coolant that will leak out. Get two pairs of pliars. Use one to rotate the short rubber hose and the other to rotate the clamp until you can see the ends of the spring clips holding the tube on the long metal pipe. Move the spring clip inward (away from the end of the hose) by squeezing the clip with the pliars.
The trick is to get the short hose off and the long hose on the metal tube running beside the block as quickly as you can to minimize the amount of coolant that will leak out onto the engine.
Use the pliars to pull the short hose off the long metal tube beside the cylinder head. Put your thumb over the hole to stop the coolant from running out. Remove the long hose from the driver's side of the throttle body and attach it to the long metal tube. Now remove the short tube from the throttle body.
You should cut the long tube to fit its new location. That takes a third thumb to plug up the metal pipe while you cut the hose. When you are done, use the hose screw-type hose clamp to attach the hose to the long metal pipe.
Check the hose to ensure that it won't rub on the alternator or the serpentine belt and that it isn't lying on the (sharp) spring clamp ends holding the radiator hose on the engine block.
The first time you get a chance, put your hand on the intake manifold after the engine has run for a while. You will notice it is much cooler than an engine that still has the throttle body heater hooked up.
Q: Will a larger, aftermarket (52mm and larger) throttle body improve performance?
A: The stock throttle body flows about 630 cfm, which is more than adequate for any non-supercharged LT1/LT4. Even the higher flowing LT4 uses the same throttle body as the LT1, since nothing larger is required. The maximum airflow through a 350 at 5800RPM is only 587 CFM, and the LT4 maxes out at about 650CFM at 6200RPM.
Note that these figures also assume 100% Volumetric Efficiency (VE), which normally aspirated engines do not achieve. High performance engines run in the 85% area normally, and the only way to approach or even exceed 100% is to run a turbo or supercharger. Factoring in even a generous 90% VE, we would have 583 CFM of flow at the LT4 redline of 6400 rpm, and only 528 CFM at 5800 rpm. As you can see the stock 48mm throttle body which flows about 630 CFM is more than adequate for even the LT4! So, unless you are planning on supercharging or the like, the stock throttle body is good enough.
Tires, Wheels, and Brakes
Q: How can I cool the braking system?
A: One of the quickest and least expensive ways is to install the 9C1 and Taxi air deflectors on your Impala. These route more air to the brakes to keep them cooler and prevent brake dust buildup on the front wheels. The special 9C1 side deflectors were a later addition to the Caprice 9C1 package. From '91-'93 the 9C1 cars came without any side deflectors at all. In fact there was a factory bulletin that indicated that the stock type side deflectors should be removed if excessive front brake pad wear was noted (pads wear much more when overheated). In '94 they upgraded the 9C1 cars to full 4-wheel discs, and added the killer front brake cooling deflectors to increase front pad life. Besides the added cooling, they also lend a unique look to the front of the Impala, since the air dam no longer wraps all the way around the front of the car: the new deflectors start heading back at the ends of the spoiler underneath the radiator and the curves out, directing air towards the brakes. They are available for under $4 each at any Chevrolet parts desk, and bolt right up to the pre-drilled holes in the radiator housing.
Q: After I drive my car, there are spiral "arms" of dark brown substance that looks like grease coming from my center caps. What is this, and how can I stop it?
A: This can be one of two things: brake dust or wheel bearing grease. You can determine this by attempting to wash it off with a garden hose: the brake dust will come of somewhat easily without a lot fo scrubbing, but the grease will smear around and take some work to get off.
The brake dust seems to happen more often when driving in humid environments. It also may be related to the particular type of tire dressing that you are using.
If it is grease, you should get your car into the dealer to have them check to see if the bearing are lubricated and sealed properly.
One last possibility is that you used oil on your lug nuts when mounting your tires. You should not do this! Try to clean off the oil with brake parts cleaner and remount the rims.
Note that applying a good coat of wax on your rims when you wash your car makes it much easier to get all of this gunk off when you wash it the next time. The brake dust also seems to stick less to freshly waxed wheels.
Q: How long will the stock BFG ZR4's last?
A: Under most normal driving conditions, including some enthusiastic driving, the tires will last about 30,000 miles. This has been stated by GM and BFGoodrich, and has also been confirmed by several list members.
When it comes time to replace them, you can usually find a good deal from Tire Rack. Look in the latest issue of Car and Driver or another good auto magazine for their latest add: the ZR4's are usually advertised for ~$140 each. If you get the tires locally, take in the ad and ask them if they'll meet the price: usually they will.
Another way to save money on tires is to join BFG's Team TA. Call 1-800-RACE-BFG and sign up. Ask them to send the rebate coupon. You can save $100.00 on a set of four. The rebate covers the ZR-4, and lasts from 3/1/96 through 11/30/96. Besides rebates, you can buy race tires (like the drag radial or R1's) for cost, which is typically $70-$100 less than the tire shops. They also send you a monthly newsletter with racing and tire tips.
Q: What sort of replacement brake pads should I use?
A: The stock pads on the Impala are very good. They stop well, don't squeak, and tend to last a long time. However, they are very expensive from GM. Also note that the replacement pads you get from GM are not the same as the original pads: they are of cheaper construction.
Raybestos makes a nice set of pads for the Impala. These are what Tim Allen used on his LT5 powered SS. Most auto parts stores should stock them. Make sure you get the top of the line pads as there are several grades available. Also note that the Impala pads are different from stock Caprice pads. Get Raybestos Premium Pads (Blue Box) , Part No. PGD 614 M.
Performance Friction make brake pads for Nascar and Indy cars. They sell "highway (-4)" and "z-rated" street pads for the Impala/9C1s. These are a carbon Metallic pad that can withstand higher temperatures to reduce fade and also last much longer than OEM pads. The "-4" front pads cost about $41.00 #6144 and the rears #6284 are about $47.00 a set. The "z-rated" pads are about $80.00 a set for the fronts and the rears aren't available yet in a Z-rated version. Thes pads put off a black dust as opposed to that rust color dust and should wash right off. Note that the "highway" pads are available from most AutoZone stores.
Note that Performance Friction will give 25% off list for any of the their products for NAISSO club members. As an example: Part #614Zm, (Front Z), list price is $84.90, which equates to a discounted price of $63.67! This is the best PF price you'll find! Contact PERFORMANCE FRICTION CO, MARK PRICE - Product Manager EXT #8143, 1-800-521-8874, 83 Carbon Metallic Hwy, Clover SC. You should mention "Impala Club" when ordering. Other useful product numbers:
There shouldn't be a problem with brake squeal as long as the rotors are properly prepared. Resurface and then sand them in a crosshatch pattern. 3M sells a sanding disk for a drill designed to put the crosshatch pattern on the rotors. The outboard clip needs to be crimped and the inboard grasshopper clip should be replaced with a new one.
Q: What size is the standard wheel and tire combo on the Impala SS?
A: The standard tires are BFGoodrich Comp T/A ZR4s in the P255-50ZR17 size. Currently, BFGoodrich is the only company to make a tire in this size. Several tires are available in similar sizes, but the speedometer will then be off.
The B body cars have a 5", 5-bolt stud pattern, while ALL Corvettes (and most other sports cars) have a 4 3/4" 5-bolt pattern. Keep this in mind when purchasing aftermarket wheels or drooling over those 315 series tires on the 'Vette.
The stock 255/50 17's are 27.0394" in diameter (the height of the tire itself, or the height of the aspect ratio, is 5.0197")
And finally, the magic formula:
Rim Size[in] + (((Width[mm] * (AspectRatio / 100)) * 0.03937)*2)
e.g.:
17 + (((255 * (50/100)) * 0.03937) * 2)
17 + (((127.5) * 0.03937)
* 2)
17 + ((5.0197) * 2)
17 + 10.0394
------------
27.0394" for the
stock setup.
Q: Is the ABS system on the Impala safe? What about this threshold braking business?
A: Threshold braking is a technique practiced by all serious high performance drivers; if made a habit, it replaces the `stab the pedal and lock 'em up' panic habit entirely, and is much to be prefered. Basically, the premise is that tires generate maximum braking force when they have just started to slide, but just before the wheels lock up entirely. Drivers who threshold brake learn to feel what this `threshold' feels like, and learn to search for it and hit it on the application of the brake pedal. In many cars, you can feel that you are near the threshold when the pedal starts to firm up as you depress it. In any case, if you can't hear the tires whine just a bit, you're not very near the threshold.
In some cars with ABS, there is a twinge in the pedal just before the system starts cycling; if the driver backs off on the pedal just a tad when the twinge is felt, then they are very close to the threshold and they'll probably achieve better stopping distances than if they just punched it and let the ABS take over. This method is primarily useful in early ABS systems; newer ones with more sophisticated multi-channel controllers do not require such methods.
Recently, there has been a rash of publicity over a number of accidents, and one death, involving police cars equipped with ABS systems. The police departments in question quickly blamed the new ABS systems, but according to Autoweek magazine, it now seems clear that the problem was a lack of training; none of the involved officers had any recent performance driving training. There is reason to believe that the drivers reacted to the pulsing brake pedal by `pump braking', an old and discredited technique of stabbing and releasing the brake pedal, the goal being to try and get brakes back with a failing hydraulic system. If you think about it for a minute, you'll realize that pump braking must cut the effective operation of a working brake system by at least 1/2, so if you cut the 40% duty cycle of an ABS system by that much, you are giving up most of your brakes for the wrong reason. Threshold braking has the advantage in that it is an effective and useful technique regardless of whether your car has ABS; if you do fear a failed hydraulic system, then one or two stabs at the pedal will be sufficient.
ABS works by monitering the wheels of the car, looking for signs of locked brakes. The Impala system can distinguish between thre different points: left and right front and rear. It cannot detect impending lockup (which is what you would really want in an ideal world), but only the existence of lockup. The sensors used vary; some of the less well designed sensors are sensitive to tire size, and to brake pad material, and may cease to function properly if the owner deviates from original equipment or OE-equivalent components.
When the sensors detect lockup, the ABS system responds by unlocking the brakes individually. If the driver keeps their foot firmly planted, the ABS will end up cycling between the locked and unlocked states (if a sensor existed that could detect _impending lockup_, then we could sit right at that point, which is where maximum braking effect is achieved.) This pulsing can often be felt in the brake pedal, as the system cycles. The percentage of the time that the brakes are truly engaged is called the `duty cycle'; typically in an ABS system this is about 40% With older systems and on dry pavement, a trained driver could beat this duty cycle quite reliably using a technique called threshold braking, but newer "multi-channel" systems appear to be able to beat threshold braking system in at least some cases. on wet pavement, braking is so chancy that ABS will outperform threshold braking nearly every time. However, in some mud and snow conditions, often maximum braking effect can be acheived with the brakes locked; only Audi, of the manufacturers producing ABS-equipped cars, has seen fit to provide a disable switch for the ABS system for this eventuality.
A particularly important feature of ABS is that it preserves steering control. Without ABS, once the brakes are locked, steering is impossible, but with ABS, it can be retained because the ABS system will release the brakes if it sees steering-triggered lockup, and back off on the percentage of the time that the brakes are applied. Braking distances will lengthen accordingly, but at least you will be able to steer the car.
An important caution: ABS cannot exceed the maximum theoretical braking force in any given situation; if you start sliding on glare ice, don't expect an ABS system to help you out very much. The coefficient of friction is not changed by the presence of an ABS system in your car.
As far as maintenence goes, in addition to the potential restrictions I've listed above, you have to worry about the following: 1) parts costs are much higher; the OE master cylinder for my obscure european sedan lists for $185, but the OE master cylinder for the ABS-equipped version of the same car lists for over $1000. Most manufacturers explicitly forbid use of DOT-5 (silicone) brake fluids in ABS-equipped vehicles. Because of the potential cost of replacement of corroded brake system components, regular (I suggest annual) replacement of brake fluid becomes very important.
Q: I'd like to get some wider wheels for the rears. Where do I look?
A: You may want to get wider wheels if you plan to run 275mm width tires or larger on the rears. These are really too big for the stock wheels, according to most manufacturers.
The Forgeline RS (used by Callaway) and the ZR6 made by ROH apparently closely resemble our stock wheels and are available in 9.5 x 17. The ROH (an Australian company) rep says ROH had the contract to make the OEM wheels for our SS, but then GM switched to Superior Industries International in Van Nuys, CA. The SS prototype shown at car shows had ROH ZR6 wheels.
Forgeline RS's run around $495/wheel, but that may be negotiable. Expe