Thread: stock V8 mufflers on a gtp

I've calculated my mileage the normal way at almost every fill up. The DIC is consistently ~2 MPG above the actual. It usually reads 24-25.

Originally Posted by bluegtp91

So just put a dump on it then. The resonator's or glasspacks do nothing to harm exhaust flow. Don't know where you get your information from but all they do is quiet down the exhaust. Like I said if your worried about obstructions in the exhaust system that really doesn't hurt it...then just dump it. I'm sure that your not even making near 350 FWHP...so the stock resonator/catback/mufflers/Y-Pipe...etc...has been dyno proven to not have any flow issues.

anything that causes turbulence in the exhaust flow will slow it down. even a gutted cat or glasspack will harm flow. this isn't rocket science Jr. here is a cutaway of a glasspack, every one of those little scoops is going to slow down exhaust flow. i'm not saying our going to lose 25hp from a glasspack, but is will harm performance.


i understand that the OEM exhaust is "good enough" for 350hp, but a better flowing one will BETTER performance than the stock one. if you honestly think that a more restrictive exhaust is not going to harm performance, your a moron.

Originally Posted by Bio248

the catback will not net you any gains even if youre making a million horsepower. only change it if you want a different tone out of it. otherwise just leave it alone and run with it. these cars just dont make power from changing up the catback. its literally unheard of. yeah, you might pick up 5-7 whp if you drop the catback at the track if you have a full blown cammed and intercooled setup, but why make the car unnecessarily louder and uglier sounding for 2 whp when youre not really modded or 10 if youre heavily modded? it just doesnt make sense to waste money on it.

WRONG.... I had my n/a setup running 14.7-14.8's with a gmpp dual cat-back. I swapped on a stock catback from a gtp and I lost 2mph in the traps and dropped to consistent 14.9-15.1's. There ya go, it's now proven with time slips as evidence ;-)

Originally Posted by OH4CompG

WRONG.... I had my n/a setup running 14.7-14.8's with a gmpp dual cat-back. I swapped on a stock catback from a gtp and I lost 2mph in the traps and dropped to consistent 14.9-15.1's. There ya go, it's now proven with time slips as evidence ;-)

Haha, I don't think so. Many variables here, temp, driver, track condition and I could go on. Quit being foolish

Actually yes, it was the same event and runs were within a few hours of each other. A local club member had a stock GTP and I was curious. I didn't just make one run to confirm this, there were a few runs done to be sure. Just because you haven't actually done it to test it out doesn't mean you can be so quick to judge. I never said that the stock cat-back isn't "good" to that much FWHP, but you're absolutely wrong if you think that you will get NO improvement from a cat-back.

Soo, you switched cat backs right there at the track? I find that hard to believe.

Do you ever actually get under your car? lol Two bolts and slide the system off of 7 hangers. Jack the passenger side of the car and you can slide the whole thing out the back. I had a welded GMPP exhaust and the stocker is also welded. Comes out in one piece. Had it in and out in 15 minutes taking my time.

Edit: I realize some of you live in states that salt the roads and this is unreasonable for you as corrosion rusts everything under your car. I live in Oregon, no salt here.

Originally Posted by Bio248

i call BS as well. there is no way in hell an n/a GP would gain or lose any power from switching the catback. youre full of it.

So you've done this then and put your own car on a dyno to prove it? Don't run your mouth, or you're calling yourself out as a bull**** artist. Go flex your E-muscle in someone elses direction.

Specs on the car were as follows.....

2002 Chevy Impala
GT1 cam
Comp 105's
Ported heads (intake and exhaust polished and blended to gasket match)
.051 MLS head gaskets to raise compression
HV3 intake insert
ZZP 1.0 PCM with tables adjusted for the GT1
Home made FWI
PLOG
2.5" cat-less DP and GMPP exhaust
I may have missed a thing or two. It's been more than a year since I've had the car. Power pole on the side of a road took it away from me.

Results may have been a little more drastic for me because the exhaust would have exhibited my only back pressure due to the PLOG and cat-less DP. I'll have to look for the slips but I promise you got no BS here. The only reason for that experiment was to see if I could get the same performance on the car out of a quieter exhaust. And I couldn't, so I went back to the GMPP.

Originally Posted by blowfishRus6

back pressure is a good thing sometimes.....

Yes it was. I bolted in a catted DP once and it felt like I had more low end torque. Don't have any proof of this one though, just the butt dyno.

lol

Originally Posted by bluegtp91

I'd just like to point out how FAIL it is port match your heads to the exhaust gaskets

LMAO!!

Look, you as well as any dumbass out there knows that you keep the D-shape of the exhaust port but you enlarge the port opening and polish the runners to match the port of your exhaust and intake manifold. Why don't you go take a look at some ported heads someday genius. You wanna talk about fail, let's talk about how much your people skills and respect for others fail here. I respect your opinions and your experience but if you don't let others bring their knowledge and experience to the table then you have no business being on a community forum. Just because people don't do things your way doesn't mean that it's the wrong way. You wanna tell me who's N/A GP or Impala for that matter you've seen go faster than 14.7 at 94mph with no power adders save for a cam? Thought not lol. Go be petty someplace else