Ok, I'm sick of posting the same thing in every thread that comes through here, so I did a bit (I know it's huge, but it's everything I could think of) of a write-up. Please critique this and maybe we can sticky it?? All input is appreciated and will not be judged adversely.
Commonly Asked Performance Questions:Before you begin doing work on your car, please take time to browse through and read the articles and write-ups in Techinfo. Our Staff and Gearheads have put hundreds of hours of work into creating these articles so they can benefit you. It will be linked throughout this write-up, but there are many more articles that I don’t have linked.
Also, if you have a question, chances are someone else has had it and asked about it as well. Be sure to take advantage of the “Search” function located at the top of the forum. Questions are welcome, but utilizing resources is important too.
What do I want out of my car?This is the most important item in this article. What I want out of my car is different than what anyone else wants, and my mods and goals should reflect my budget, goals and personality. Before you turn a single wrench, sit down and set your goals for the car. You don't want to do things twice, just because you did them once for maintenance, and once for mods, EG: Doing LIM gaskets, then turning around and doing them again upon installation of a performance camshaft, or top-swapping a N/A car. Whether it's a daily driver that you want to look, sound and drive better, or a full-out weekend toy/track beast, you need to set your goals and figure out what you need to do to make them happen, so you're not disappointed in your outcome. Your goals can always change, but if you don't have any, it's hard to meet them.
Can I supercharge my non-supercharged car?The simple answer is yes, but not easily or effectively. Your best bet will be to get a car that comes supercharged from the factory. Not only are the engines and transmissions designed for the abuse, but the cars also generally have better suspensions, leather and more interior features, and different body cladding.
On
Series I cars (N/A RPO code L27, S/C RPO Code L67), it is strongly discouraged to attempt to swap a supercharger onto the stock L27 engine. It has been proven that the bearings and other internals have failed after very few miles.
viewtopic.php?f=44&t=194If you feel you do have to supercharge your L27 car, the best plan is to remove the entire drivetrain, axles, wiring and PCM (Powertrain Control Module) from a donor L67 car. The next best is to swap in just the L67 engine and wiring.
On
Series II cars (N/A RPO L36, S/C Remained L67), it has been proven that the L36 bottom end will handle boost. However, it was not designed for boost, and is at a higher risk of failure. Your best bet is still a full powertrain swap from a donor S/C car. That way you get the stronger pistons, rods and transmission. The next best is to swap in the L67 engine and wiring, and the least strong is to swap on the heads, intake, S/C, Harmonic Balancer and accessories from an L67 car, then add the wiring and get the proper tune or tuning software, making sure to start with the stock size (3.8" diameter) pulley, seeing as the higher compression of the L36 engine is already like running a smaller pulley.
More Information: viewtopic.php?f=44&t=1687I want to make my car faster, what are good first mods?The first mods you need to do are maintenance. It’s hard to make your car go faster if you have lingering issues like misfires or poor engine efficiency that are affecting your power output. Following the Maintenance List will help prevent these issues.
Any gasoline engine requires 3 things to run, Air, Fuel and Spark.
Spark: The 3800 has a good ignition system to begin with, and as long as basic parts are kept in good repair (namely spark plugs and wires), there is no need to “upgrade” any of the other parts, except for changing the heat range of plugs on forced induction engines as boost and power levels increase.
Intake: Stock air-boxes are designed for emissions and keeping the engine noise to a minimum, not making the most power. Gutting the restrictions in the air-box can help, but the best modification is to install an intake that either locates a conical filter outside of the engine bay (Fender Well Intake) or a sealed box that isolates a conical filter from engine bay heat, both using an insulated tube that provides laminar flow.
Series I Airbox Mods: viewtopic.php?f=44&t=22280Exhaust: Exhaling is important too, but this is where the two Series’ again diverge.
Series I: You have arguably the best exhaust manifolds GM ever made. The only improvements are to remove them and have the cracks welded, and have your stock catalytic converter replaced with a high-flow unit. Magnaflow is a popular brand that is of high quality.
Series II: The Series II doesn’t have such nice manifolds. For cars with fewer mods, a good upgrade is to replace the stock downpipe (exhaust tube between the rear manifold and catalytic converter) with a high flow unit (N/A should get 2.5”, S/C should get 3”) and a high-flow cat. ZZ Performance makes downpipes in either mild or stainless steel, and you can have them install cats, only needing welding to the pipe that connects the cat to the resonator. At higher power levels, ported exhaust manifolds or headers are the next upgrade. Here is where your goals come into play. If you plan on trying to run 13's, you're better off installing headers first, instead of going to a Downpipe, then later upgrading and having to re-do that work, along with sell used parts.
On both of the cars, the rear of the exhaust is perfectly fine for all but the most powerful 2% of cars that this forum has and will ever see. 350 WHP and up might see a small improvement from adding larger diameter exhaust tubing and better flowing mufflers.
Cooling: The lower the temperature a group of molecules is, the closer together (denser) they become, as you might remember from HS Chemistry. However, this affects your engine in a big way. If you can keep the air that comes in cool, you can fit more molecules in your cylinder and with that additional air, you can add more fuel. More air + more fuel = more power. One simple way to do this is to do a thorough coolant flush (you should be doing this anyways with your basic maintenance!) and installing a thermostat that is colder than stock. Stock on 3800’s is 195°. For a vehicle that is daily driven in climates where temperatures will get below freezing a 180° thermostat is recommended. If the vehicle is a summer only or race only vehicle, a 160° is a suitable thermostat. There are other issues that can come up with using a 160° thermostat, namely the PCM not reading KR (KR will be discussed later), and having issues running emissions tests. You will also need the PCM tuned to change fan turn-on temps to turn the electric cooling fans on at the temperature that reflects the temperature of your thermostat, as well as reduce temperatures for emissions tests to self-test at.
Reverse Flushing Cooling Systems: viewtopic.php?f=45&t=15064Fuel: While it is true that the PCM can monitor the air going in and add fuel, it can only do so thinking it has 100% stock pieces. The only way to change this is to have someone with tuning software (HP Tuners and or Digital Horsepower (DHP) PowrTuner) go into the PCM and change settings, including those that add fuel and adjust ignition timing to benefit the mods you have already installed. Someone experienced with the software and 3800’s should be left to this tuning, unless you plan on learning yourself and the risks associated. Series I cars only have the option of having custom burned chips for their tuning. Other options are an Adjustable Fuel Pressure Regulator (AFPR) with a MAF Translator. More fuel pressure will force more fuel through the injector during the time that it is open, and the MAF Translator will allow you to change the MAF’s (Mass Air Flow Sensor) signal to change fueling. A Wideband O2 sensor is mandatory when using a MAF Translator and AFPR and recommended with a PCM tune. That way you ensure proper fuel ratios to reduce the risk of engine damage.
Injectors: One common misconception is that adding larger injectors will give you more fuel. The only vehicles this has ever been true on is diesels. Adding larger injectors will allow you to add more fuel via PCM tuning to match more air flow, but they don’t add fuel just by installation. They just give you a higher flow potential versus stock injectors. The only way to know if you are maxing-out your injectors is to scan and tune it. A properly maintained fuel system will handle mods up until you start adding more air via valvetrain mods.
Fuel Filter: viewtopic.php?f=45&t=23215Supercharged Cars: All of the aforementioned mods are for both supercharged and non-supercharged cars. However, this list is just for supercharged cars.
Supercharger Pulley: Before you change supercharger pulleys, you must have done all maintenance and supporting mods FIRST. Supporting mods are everything listed above, an Intake, cooler thermostat and preferably exhaust mods, along with a PCM tune. Knock Retard, or KR, is the PCM’s reaction to fuel burning in the cylinder before the spark plug ignites, due to excessive heat. Premium Unleaded gasoline is an absolute necessity in supercharged cars. You must get a scan tool that is capable of reading KR, and you must read your KR on the hottest, most humid day you can, as that is when KR is most likely to strike. Once you have the engine tuned up and with supporting mods and a tuner waiting, you can then swap on a smaller pulley.
92-93 Eaton M62’s are equipped with a 2.55” Pulley stock. The first step down is a 2.3” pulley, scanning for KR before and after.
94-95 M62’s come with a 2.80” Pulley, and the first step down is a 2.5 or 2.55 (stock 92-93) pulley, again scanning for KR.
96-07 Series II and III M90’s come equipped with a 3.80” pulley OEM. The next step down is a 3.6” pulley, scanning for KR, and when using race-gas a 3.4” may be used depending on mods and KR.
M62’s have a keyed shaft, which allows them to use a standard 3 jaw puller to remove the pulley, while M90’s use a tapered shaft, which requires a special puller that supports the whole pulley. Most Series II/III owners generally utilize a Modular Pulley System, which is a pressed on hub that pulleys bolt to. Any vendor that sells pulleys or MPS setups will sell the puller necessary for the M90. Some rent them as well.
Stepping down in pulley sizes will either require shorter belts, larger tensioner pulleys or some combination. One exception is running a 3.6” pulley on a stock belt, there is enough room on the self-tensioner that it can take up the slack with no adverse effects.
More Information: viewtopic.php?f=44&t=1660Transmission: The stock transmission in these cars is a relatively good piece, considering it’s a heavy FWD Sedan. Keeping clean, cooled fluid is a must. A separate transmission cooler and doing regular maintenance (Dropping the pan and replacing the filter every 15-25k) will help the transmission live a good life. A shift kit will also help this by lessening the slip in-between shifts, which will be easier on clutches and hard parts in the transmission. Having the PCM tuned to improve shift times will also help the transmission live longer (OBD II). Cars equipped with the 4T60E (1987-1996 S/C and 97 N/A) can benefit from an adjustable vacuum shift modulator installed, which will allow you to dial-in your shift pressure to a certain extent.
2000-2005: One part that is unique to the 00-05 (00+) Bonnevilles is the front transmission mount. While the stock one is prone to failure, this is one opportunity to upgrade for very little money. Many members have replaced their OEM mount with a “Hockey Puck” mount, using stacked hockey pucks and washers with a long bolt or section of all-thread through them to help reduce engine and transmission movement which will allow all your power to go to your tires quicker, helping your car hook up more consistently and better.
Transmission Pan Drop and Filter: viewtopic.php?f=45&t=10193After these basic mods the sky is figuratively the limit. There are many other mods from cams and intercoolers to upgraded superchargers, etc. We can help you whether you want a little more boost in your daily drive, or a car that will put down very respectable numbers at the dragstrip. I hope this write-up helped answer some of your basic questions.