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3.5" Pulley/ Exhaust

J

JGSuperCharged

New member
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.
 


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.
 
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.
 
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.
 
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.
 


JoRoW99 said:
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.
Click to expand...

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
 
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.
 
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?
 


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.
 
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.
 
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.
 
FordMan77 said:
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.
Click to expand...

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.
 


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