3.5" Pulley/ Exhaust

[JGSuperCharged]

Hello fellow Prix owners, you guys rock. A month back i bought a used 1999 Grand Prix GTP Supercharged. It has about 175,000 clicks on er, and is bone stock. I've been impressed so far with how fast it can go, except i want it to go faster. Today i installed a K & N Cool Air Intake Filter, haven't quite noticed much of a difference but i guess i'll take the manufacture's word for it and assume i'm getting more power. I've read that a new pulley for the supercharger is a good bang for your buck HP booster. Would i be able too install the 3.5" pulley as is or are there any other mech component's i should consider upgrading to help the car deal with this extra HP. Also I'm not a fan of exhaust system, or atleast the exhaust tips, can i install new tips myself? and which exhaust tips/ upgrades are best for the GTP? Thanks guys, these forums are legit.

[JoRoW99]

Well you should have just made your own intake, and I wouldnt believe the manufacturers claims. You can find a cheap set of headers off ebay for $200 and they will replace the restrictive front manifold and infamous u-bend. exhaust tips are only for looks, and yes you can install them yourself. the clamps may be really rusted on there though. get whatever tips you like, dual/duals are very popular. you may be able to get away with a 3.5 on your basically stock engine, but you would absoultely need a scan/in car/dyno tune with it.

[benner]

Read this and treat it as your W-body Bible.

http://www.grandprixforums.net/safel...car-17482.html

[Tuner-Extraordinaire]

Upgrades or bust.

On stock guts/intake, exhaust flow. You will be pushing about 10% more air through the car. You will see more boost with a 3.5 pulley, but buddy, boost aint what you want. 3.5 pulley on stock drivetrain = boost stacking.

[JGSuperCharged]

Awesome link, thanks. What do you mean by Boost Stacking? As read in the bible, looks as though i'll be buying new spark plugs/wires next.

[JoRoW99]

you dont need colder plugs yet really.

boost is a measure of restriction. for example, my car sees 5 lbs of boost, 6 max (rarely). a stock GTP sees what, 10? all my flow mods increase flow which means less restriction and less boost, yet more power.

[Tuner-Extraordinaire]

you dont need colder plugs yet really.

boost is a measure of restriction. for example, my car sees 5 lbs of boost, 6 max (rarely). a stock GTP sees what, 10? all my flow mods increase flow which means less restriction and less boost, yet more power.

Depending on air density and temperature, A stock GTP or other L67 powered car will see 4-11psi on a stock pulley (YES, i've personally seen it vary by that much.)

Colder plugs on stock pulley....I'd go 605's, if you go 3.5 pulley, go 104's

[JGSuperCharged]

Thanks. So for example i aspire to go with the 3.5" pulley, if i were to put that in tomorrow, how would my car respond?

[JoRoW99]

Probably not that badly. BUT I would rather be safe than sorry and get a tune at the same time.

[Tuner-Extraordinaire]

With no other mods?

If your car wasn't knocking before (doubtful) -- It will after you slap a 3.5 on it.

You might feel a seat of pants difference of ~10hp, maybe 20lb-ft tq to the crank. Hardly enough to be measurable. -- This is because your car will be pulling timing.

[JGSuperCharged]

KK. I read in another thread that you risk blowing your motor with that kind of power, what would balance the pulley out to avoid any potential drawbacks?

[JoRoW99]

Its not the power that would blow the motor, its the knock. And headers would balance it out, or at least a 3" downpipe. I really wouldnt run any more boost without scanning for knock.

[FordMan77]

Headers, highflow cat and a Aeroforce scangauge and tuning software would be a good start. Then maybe some diff. plugs. Just read through the link posted on safely modding the 3800. Could you run the 3.5" w/ no flow mods? Sure. But how long, probably not very. Then you will learn the hard way as you chip pistons and are finding a new longblock.

[ItHurtz]

headers, tune, 180tstat

[JoRoW99]

IMO I wouldnt run a colder t-stat. I know that most people on here will disagree but i dont see the point. heat=power.

[Tuner-Extraordinaire]

Headers, highflow cat and a Aeroforce scangauge and tuning software would be a good start. Then maybe some diff. plugs. Just read through the link posted on safely modding the 3800. Could you run the 3.5" w/ no flow mods? Sure. But how long, probably not very. Then you will learn the hard way as you chip pistons and are finding a new longblock.

I'm sure you could run a 3.5 forever with NO flowmods. As long as you didn't punch it too often.

The point is, pulley and no flow mods = negligible gains, and decreased reliability.

[JGSuperCharged]

Ok, so from what I've read in the bible, it's either you upgrade the downpipe and front manifold or you purchase headers. Which option is better?

[Tuner-Extraordinaire]

Headers.

[whiney]

Headers by far are the best option, then with a decent tune you could be looking at a 3.4" setup

[JoRoW99]

As far as I'm concerned, PLOG and DP are obsolete.