VALIANT

How to Begin Mods to Your Grand Prix

(or any 3800 SC car)

Questions to ask are

• Can you do complex installs yourself?
• How much do you want to spend?
• Will you continue to upgrade your car in the future?
• Do you have a factory warranty?


For every person the SC pulley swap should be the first thing considered. It offers the largest HP/dollar value of any mod. You will need a special tool to do the install which can be bought or rented. Install time is about 1 hour. If this is the only mod you plan on doing then the 3.5” pulley should be used. The stock belt can usually be used but I recommend the 4060660 belt or an oversized tensioner pulley. The 3.5” pulley swap will give you ~20 additional HP.

If you plan on doing other modifications as well then the 3.4” pulley is a better choice. It requires a smaller belt or an oversized tensioner pulley. The 3.4 will give ~25 additional HP. Supporting mods include colder Thermostat, stage 1 throttle body, colder spark plugs, cold air intake, TB spacer, any other form of exhaust modifications. I recommend at minimum doing the U-bend delete.

Available octane plays a part as well. If you live in a state with only 91 octane available you will need to do additional mods to run a 3.4” pulley without KR. You might want to consider the 3.5. If you live in Indiana or parts of the country with 94 or 95 octane available, it will be very easy to run the smaller pulley w/o KR. Keep in mind that a larger pulley with no KR will make more HP than a smaller with less timing (more KR).

If you plan on continuing to mod your 3800 in the future you should buy a modular pulley system. The assembly is lighter than a press on but more importantly, it will make future pulley swaps very easy without needing to use the puller tool again. Then as you mod your car, you can buy smaller pulleys. This will allow you to run one size pulley for the street and one for the track or when using race gas.

After or along with the pulley you should run a colder Thermostat and colder spark plugs. The 160 is the best choice but doesn't work very well in winter operation. You can switch back to stock for winter use or buy the 180 and use it year round (99+ cars should use a 180*).

For a colder spark plug I recommend the NGK TR6 or TR6ix. These plugs will help to lower KR. New plugs will also increase the performance and gas mileage of a car with used plugs. Many people run TR55's but we have found no ill effects of running TR6's and they work better for getting rid of KR.
If you have a 97 or 98 then a CAI is a very good choice as your next mod. If you have a 99 or newer your air-box is a little better and you can postpone doing a cold air intake if you install a K&N filter. The Wizaired airbox will give excellent gains and help reduce the KR that you will most likely be getting from running the smaller pulley.

Exhaust should be considered at this point. The U-bend should be your first part of the exhaust to upgrade followed by the resonator, then down-pipe. After that your exhaust manifolds are the most restrictive, then your piping to the Y section and finally your pipes to the stock mufflers. The factory mufflers are not restrictive and should be changed based on looks/weight/sound before all else. Once you're making over 300WHP then we can talk about the performance aspect of mufflers. The U-bend and/or resonator should cost $50-100 to be replaced by a local exhaust shop. You'll want to pick up an O2 simulator if you are planning on eliminating your rear O2 sensor. And yes, this stuff is all emissions legal as you are not messing with the operation of the cat. Exhaust work is an excellent way to get rid of KR when running smaller pulleys.

Easy mods from here include a water pump under-drive pulley, and a throttle body spacer. The Spacer will help get rid of KR, the WP UD pulley will free up a few top end HP. Both are inexpensive ways to continue the pursuit of more HP.

The PCM is an excellent mod a this point. It will help lower KR, and make driving the car a much more pleasurable experience. It increases HP, changes shift points as well as fueling, makes the car shift harder under "Performance shift mode", takes away your top speed limiter, raises your rev limiter and has a few other tweaks. It will lower your gas mileage slightly and increase the chance of tranny failure (due to firmer shifts) but at your HP level now you shouldn't have to worry about the transmission yet (also it would be wise while you are getting the trans. Beefed-up you man want to invest in a limited slip dif. and a torque stall converter).

At some point above you are going to want to consider Poly Motor Mounts and a shift kit. The shift kit in combination with the PCM can break hard parts in the transmission so that is something to be aware of especially if you have heavier rims/tires/brake rotors than stock.

You are now done with the easy stuff that most people do. From here you need to decide how far you're going to take your car. This will help you make the decision between high ratio rockers and an after-market camshaft. If you plan on being faster than mid 13's or make more than 280 to the crank HP you're going to need to do one of 3 mods. Rockers, intercooler, or Cam. Rockers add ~25HP, increase gas mileage, do not change reliability of the car, cannot be seen by the dealer, are relatively easy to install yourself and will support low 13's without an intercooler. They help the engine flow better, lowering KR and allowing a drop in pulley size by about .1”.

Combined with an intercooler many GTP owners have taken a 3800 with stock camshaft, rockers and an intercooler deep into the 12's with close to 300WHP. Bang for the buck rockers are an awesome mod.

I think I will keep the rest to myself… If you have any further questions, feel free to ask me…

Quik

Great info!

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sometimes i ban slow, sometimes i ban Quik

joez69

thats all great info but u shud go into detail about more hardcore mods also. for example im in the process of building a custom twin turbo set up for my grand prix gt. also u cud check intense-racing.com as they hve gtps that do 9 seconds in 1/4 mile. there isnt that many mods u can do to a grand prix unlesss u build the part ur self.but for all the basic stuff u hit the nail on head great job!!!!!!!!

GTP2fast4u

ok by no means should the pulley swap be one of the first things considered! i am not trying to start a argument but i just thought i would say this before someone smokes an engine due to false info

ok to start off KR does more damage on GTP's than GT's because of the forced induction and intake air temp is higher.

I tune cars ( ive tuned 5 or 6 L67 powered vehiclesm and 3 L36's) most GT's have atleast 6* KR stock
but even worse almost all GTP's have KR stock 2 or 3 * to begin with. by swapping a s/c pulley from a 3.8" to a 3.5" you are adding ( if you figure 2*'s for each pulley size, and that isent really alot) your at almost 10 * KR right away. that is super bad.

this is the MINIMUM you should do BEFORE YOU SWAP A PULLEY

CAI/FWI
U-bend delete
3" D/P
PCM
180* T-stat (drilled prefered)
1 heat range cooler plugs (copper core prefered)
A scanner is highly recommended in order to monitor the KR that will be introduced with the smaller pulley.


and by just swapping the pulley before you do any supporting mods, your not only risking hurting your engine, but in some cases the car will actualy slow down ( and i have seen this before) where the PCM retards the timeing so much, that its at * retarded not * advanced liek it should be.

please dont come back saying "well i ran a 3.? pulley for 3 months and was fine"
yeah your Knock sensors picked up your pre ignition and retarded your PCM enouh to save you ......but your friends and fellow GP owners might not be so luckey

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MIGPC_DustinC

if you have a Gen 5 M90 you can easily run a 3.4" pulley just by running AL103's because it is far more efficient than the Gen 3 found on the 97-03, but supporting mods are still highly recomended

180* T-Stat is great but dont run a drilled one in the winter if you live someplace like MI.

dont run a 3" DP if you have a cat-back that is 2.5", also running 3" all the way will cause you to lose a noticable amont of low end TQ

U-bend delete should be the first thing any 97-03 GTP owner does it will lower your KR and make your exhaust flow less restricted, 04+ do not have a u-bend but a down pipe is still a worth while mod.

even if you dont plan on building for speed a intercooler is a great thing to do just for added security

04goat

thanks alot for all the info. my son has been trying to find something on the web. he has a 04 gtp and already has a intercooler to put on... thanks his dad appreiates it!!!!

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2004 gto yj 6sp tb bypass, maf screen delete,polished tb, 238/248@50 600/605 112lsa,pacesetterlt's,custom 3 1/2" single mandrel bent exhaust,stock #'s 309rwhp, 344rwtq,after mods 398.44 rwhp and 389.52 rwtq, 12.7 @ 109 w/ slipping clutch on dr's, ls7 clutch and flywheel in the works.