stock shortblock 302 with GT40 irons, 2031 cam, Performer EFI intake, and a 60-1 T04S/P-trim .96 (also have a .81 A/R). This is an old TTI street kit that mounts the turbo on the driver side. I don't have any room to increase the downpipe to 3", so I am curious how much I am giving up with a 2.5" downpipe. Once it passes the firewall it splits into dual 2.5" pipes. I am hoping to make in the 450-500rwhp range on around 12psi and 93 octane.

 

The p trim exducer is larger than a 2.5"pipe.... I would avoid it if at all possible. 3-3.5" is what you want.

 

2.5" id or od? I run a 3" od which is 2.75 id. 500rwhp is not a hard goal, just run it and see where it gets you if you already have it. If it's not built I'd go with 3" fr sure.

 

Ideally your dp should be turbine exducer x 1.25 or larger.

Do you run a 3" on your s366? 80/73 turbine?

 

Yeah 3" dp on my s366 80/73.

 

Single 2.5" downpipes are borderline on 300hp four-poppers, so I would expect one to be undesirable on a 500rwhp engine.

You run a 0.125" wall downpipe? Holy crap, it must weigh a ton.

 

Guess I'll need to find someone who can manage to stuff a 3" pipe in there. Any suggestions in the central Texas area? I'd do it myself, but it's really tight around the SN95 brake booster, master cylinder, and steering shaft.

 

Re: How much will a 2.5" downpipe hurt me?

I did a 3.5 on the pass side, it barely fits. Exhaust manifold has to be removed to get it out, since i couldnt get a band clamp to seal , so i welded it up. Thats a 2in log too.
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maybe try and oval the 3" pipe where needed.

 

thats not going to work for your hp goals, i have a twin turbo setup, 2 3" downpipes come down, go to exhaust cutouts, or with the cutouts closed it dumps into 2 2.5" pipes for the exhaust system, car will only make 600 hp thru the exhaust system, or 794 thru the cutouts(rwhp), and it won't make its normal boost psi thru the 2.5" exhaust.

 

You have mufflers and the cutouts before the mufflers?

 

cutouts before the mufflers, in the 3" pipe before it becomes 2.5", and i have magnaflow mufflers, so the exhaust system itself isn't all that restrictive, other then the 2.5" pipes.

 

The straight through kind?

 

stainless steel, straight thru. i was surprised, i thought 2.5" would support more hp

 

Regular 16g tubing. What is the true id on 16g 3"?

 

16ga thickness tubing has a nominal wall thickness of 0.065", so the ID of 3.00" OD 16ga wall tubing should be 2.875".

I suspected it was just a typo.