Exhaust Question!

jessiebighamKC · #1 03-06-2009, 05:04 PM

Ok heres my question! I Have a 2001 Pontiac GrandPrix GTP.I have to replace my exhaust manifold's both front and back and I have to replace my cat converter, Im also going to get the U-Bend delete, and Im going with 2 Flowmaster Mufflers. Should I go with I think the stock size which I think is (2" or 2" 1/4) or should I go with 3"? This guy that I know tried telling me that the car would never move with 3"exhaust and also said that the car dont run 11's in a 1/4 mile and I dont need 3". Now should I go with the stock size or alittle bigger or should I put 3" pipes? Also Is there enough room to do 3" pipes? And is there enough room or can I do true dual exhaust? Im going to be putting the car in the exhaust shop in 2wks once I get all the money saved up.

UKtech · #2 03-06-2009, 05:36 PM

I've built a 3" system for a customer at their request even tho i advised them against it (Sometimes people just don't listen to advice

),it really is overkill in my opinion..... it is a tight fit requiring some clean bending. Theres no point having a huge exhaust diameter if your not going to do some serious induction work. 2 1/2 is what i would go with.

jessiebighamKC · #3 03-06-2009, 05:52 PM

Well I do have cold air intake and I do have a smaller pulley but just havent put the pulley on yet. But I guess I will just go with like 2" 1/4 exhaust or maybe 2" 1/2 tops.

BNaylor · #4 03-06-2009, 05:59 PM

The outer diameter on the stock exhaust system is 2 1/4" (2.25). At the downpipe there is an inner pipe so it is maybe around 2.0". Do you plan on using the stock downpipe?

Go with 2.5". Best all around. That is what I have.

tblake · #5 03-07-2009, 12:56 AM

I've heard of people losing low end torque with 3" exhaust systems, and since thats where we do most of our driving, it would make no sence to run 3".

BNaylor · #6 03-07-2009, 11:13 AM

Not so much on the L67 engine even though it will affect low end torque. It definitely affects the L36 NA engine like any exhaust mods, especially headers. We can make up the difference in our GTPs and actually gain on the high end.

IMO the biggest issue with 3.0" is properly hanging the exhaust system not getting the annoying thumping and rattling sounds. Making contact with the undercarriage. Plus you need some backpressure.

UKtech · #7 03-07-2009, 07:10 PM

I agree with BNaylor , the GTX i built the system for about a year ago now lost low end torque on the dyno compared to the stock system,the customer claimed it was better on the road but more noise does not mean more performance. I also remember the guy ignoring me and fiting a generic cone style air filter rendering his ram air useless and trying to tell me it was better. I challenged him to dyno run it and prove me wrong but he has yet to come back

jessiebighamKC · #8 03-07-2009, 08:42 PM

I dont know if Im going to use the factory down pipe. I will probably just get a new aftermarket downpipe.

BNaylor · #9 03-07-2009, 08:44 PM

Thanks for that good info UKtech. The ones that get me are the GT/SE owners that install a 3.0" downpipe, 3.0" in/out aftermarket hi-flow converter, 3'0" plumbing back to the mufflers and wonder where the low end went or why some GTI blows their doors off.

Same thing when they install headers.

The other thing I hate like on CATBack exhaust systems is the deletion of the stock resonator and all that extra noise generated. It will give you a headache on long trips and you get that popping sound on deceleration.

Anyone with a GTX that gets rid of the Ram Air system needs to think about that decision. I recall the GTXs were reworked by SLP for GM.

grandprixgtx00 · #10 03-08-2009, 05:14 AM

Quote:

Originally Posted by BNaylor

I recall the GTXs were reworked by SLP for GM.

yup, and my GTX has SLP exhaust. as far as removing the ram air for cold air cone filter...what an idiot

tblake · #11 03-08-2009, 12:31 PM

I didnt know GTX's came with a ram air setup. Would there be any way to modify this to fit into a GTP? Would there be any praticle gains, I suppose not with a supercharger already.

grandprixgtx00 · #12 03-08-2009, 02:34 PM

Quote:

Originally Posted by tblake

I didnt know GTX's came with a ram air setup. Would there be any way to modify this to fit into a GTP? Would there be any praticle gains, I suppose not with a supercharger already.

theres a few options 3800performance (click link) actually has the SLP set up, and the hood can now be found here

the hood was discontinued by SLP, however american sports car design is back up and running under Stinger Fiberglass Design.

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