I want to put on my own exhaust on my gt. Not sure if I should go with a 2.5" or 3" downpipe and which mufflers and cat to go with. I do want it to sound nice and not have that raspy sound that a lot of people have.

2.5" would be plenty big enough for a gt, probably bigger than needed. To need 3" piping you have to be moving some serious air. Hogan performance makes nice downpipes, also wicked nicky's store on ebay is a good place to get mufflers like borla, flowmaster at a good price.

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Steven Oliver
2004 GTP comp-g WS6. Gator and suede all around interior.
Advanced MECP certified installer, custom upholsterer.

Well I wanted to put a turbo on it sometime but didn't want to change the exhaust later if I really wanted to. Any big sound differences between the two when it comes to the gt?

If you want to do a turbo later then don't touch it until you can afford the turbo. Big exhausts KILL a N/A car. I had a 2.5" SLP loudmouth system on my mostly stock GT and the car felt incredibly soft off idle and in the mid-range. I switched back to the stock exhaust system and immediately the car felt more responsive and more fun to drive.

The only aftermarket exhaust I would probably recommend for a GT is the Borla, since it reduces back down to 2 1/4" after the resonator and 2" after the Y split. Velocity is everything on a N/A motor.

As far as the downpipe, you'll have to change that out when you go with the turbo anyway. No downpipe that bolts up to the stock rear manifold will bolt up to the downpipe of any turbo system.

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Silver Teal Metallic 1998 GTP Sedan - 62k

Thrasher CAI, S1 HVTB, Trannyman ported blower, VS, Silver TOG's, R/T Cat, SLP Loudmouth, 42.5#'s, 3.2, PowerTuned

I agree with Coogles to not change anything if you plan on going turbo. You are not going to be able to find an exhaust setup that is perfect for both the NA and the turbo. If anything, set it up now for an exhaust that would be perfect for the turbo. Then it will make you want to get it more because of the lack of power.

But with the turbo you need to have a more open exhaust to move the air out. With the NA, you want a smaller exhaust to create back pressure. If you don't have that back pressure, you will lose power.

If you just want to improve your sound right now, I would consider just removing the resonator. I did this on my first GTP and it sounded pretty good. And it is a cheap way to go about getting a little more noise from your car.

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1997 GTP - 200k+ miles, PEMs, 3" SS Exhaust w/ Borla Mufflers, 3.4", 180* stat(summer), FWI, 1.84 RR, PT, SLP hood, KYB GR2s, GMPP Handling Kit, etc...

I have a couple vids I will post up. The both are the same exhaust setup, except the first one I will s/c and the second I am turbo. S/C'd I had headers, no cat no res and custom 3" pipe to the "Y" 2 1/2" from there going through turbo mufflers (not sure who makes them). For the turbo vid I am running a front plog and custom rear mani, otherwise the same as the s/c'd vid. I know the fist vid sounds like crap when I rev it up, and the second doesn't sound a whole lot better either...........................

Video of Exhaust vid w/ turbo mufflers - Photobucket - Video and Image Hosting


Video of ST2 idle - Photobucket - Video and Image Hosting


BTW don't worry about the rough idle in the second vid, there is something wrong with my car.

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Red 2dr 99 GTP: Z7 t66, A/A IC'd, Custom Heads, 65# Inj, ST2 Cam, Meziere Elec Pump, JP Double Roller(with machined crank gear), Plogs, PLX W/B, Powrtuner

99 Regal GS (work car)

Not to hyjack this post,, but I have a 2005 Grand Prix super charged,, and want a nice sounding exhaust system.. not overbearing but nice and rumbleling would be good.. what is the best system and where to buy.... I like the rumbleing hum,, not very loud though,, just to let people know I have a mean ass car

Is your car modded at all or do have plans to mod? If not, you really don't need a full cat-back exhaust system. All you need to do is have an exhaust shop put a section of straight pipe in place of your resonator and pick some muffers of your choice to replace the stockers. Many people seem to like the Borla ProXS because of its deep, smooth tone, plus thy're pretty quiet. If you want something a bit more aggressive both in tone and volume I think the Hooker Aero Chamber sounds really good.

Hope that helps.

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Silver Teal Metallic 1998 GTP Sedan - 62k

Thrasher CAI, S1 HVTB, Trannyman ported blower, VS, Silver TOG's, R/T Cat, SLP Loudmouth, 42.5#'s, 3.2, PowerTuned

i have a full 3 inch on my gt and i love it, of course i am going to be upgrading my intake in my ride to match that massive exit...lol

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http://www.cardomain.com/ride/2556536 NKG Iridium Plugs, 8mm Spiro Wires, ZZP Reprogrammed PCM, ZZP 3" full cat, ZZP Ceramic Coated Ported Manifolds, ZZP HV3, ZZP HVTB, ZZP ER Ratio Rocker Arms, ZZP Drilled 180* Thermostat, MotorSports Performance Intake, Reptile's IAT and dezldave tuned

for the GT...2.25-2.5. I had a 2.5 on my old GP......wicked topend but a dog off the line...I couldnt even chirp the tires when I floored it it was sooo bad.

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2001 GTP street car- GT45 turbo,Stage 4 Intense turbo cam,FMIC,150 wet, double roller timing chain, Diamond forged coated pistons 8:0:1, Diamond piston rings, cryoed L32 connecting rods, Cryoed crank, Clevite77 main bearings, Clevite77 cam bearings, Clevite77 L32 rod bearings, ARP Everything, Intense/meizere true billet Flexplate, Custom UIM, Intense oil pressure kit, Cometic 4 layer head gaskets, OE-R lifters, Cryoed L67 block, ATI turbo dampner, MUCH MORE, 6 more to choose from ASE Certified