North American Turbocoupe Organization

Exhaust flow enough for a 3"?
Matt S Offline
Posting Freak
Ok, please don't flame me. I've spent all night here bored at work reading every post with the word "exhaust" in it only to find out:
1). Cingular now owns my ass as of midnite [Image: frown.gif]
2). There is great controversy still with either a single/dual 2.5" or 3" after the muffler.

I've read from people who swear on a 3" single exhaust only to learn they themselves have 2.5" single after the muffler. I also saw a post that the flow rate goes in order of 3", 2.5" dual, and 2.5" single. I've also read that those who DID put 3" after the muffler have problems with it hitting things when going over bumps.
Me: I'd rather do a single exhaust for the cost savings and just tuck it under the bumper outa sight.

So here's what I'd like to do:
Signatures don't all mention exhaust setup, but this has to be one of the most asked questions next to "what mods do I need".
I will be more than happy to make a list for the FAQ or whatever of all the top hitters and what their mods are in relation to the exhaust setup they have. Some good solid numbers to help those of us confused make an educated decision rather than the seemingly automatic "you need 3inch all the way" answer.
If anyone has any input so far as flow numbers related to the 3 different setups that'd be great too. Please include your before and after setup, or any changes you did and it's results. The post in the mods section by someone who fooled with tail pipes and did the seat-o-pants measure was great! Helped me understand what I'm getting into.

What I *THINK* I got out of reading everything is that someone like me planning mild mods maybe up to 300 crank hp probably only needs a 3" down to 3" cat and muff. After that, a 2.5" would probably do me fine aand the hassle/cost of hanging 3" tailpipe is not worth it. I'd like to see the answers with a tone of "depends on what mods you plan to support it". Bigger exhaust is nice, but 3" through is not needed on a stock engine, right?

If this sounds of value to someone, I would love to arrange this for the FAQ section. Not noise, not brands, simply performance. PM me or email me from my profile.
I won't post my email due to web bots that search and spam me.

[This message has been edited by Matt S (edited 02-17-2004).]
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tlswart Offline
Senior Member
Purely from a geometric point of you, 2.5" duals have 2.8 square inches more area so should give you more flow under the same pressure. If running duals the problem is in designing a transition from the 3" to the 2 2.5" without causing turbulance and back pressure.

Terry: 88TC, 5spd, Gillis valve.

Pete D Offline
I haven't done the math, don't know how to do the math and from what little I can understand from those that have the smarts and education to understand all the variables, it would make a Cray puke on the calculations.

What I think is that at 300 HP, a 3" through the muffler and then 2.5" single over and out is not going to hurt you. But that is strictly my opinion based on extensive conversations with the barn door.
Pete Dunham


GaryS#2 Offline
Posting Freak
I'm with the 2.5" single TP crowd now.
I used to have a 3" ghetto rigged under the axle thing, but in my trials and errors just kept the 2.5" single.
If I ever push the 300 hp mark I may worry about it then, but figure the exhaust does cool by the time it gets back there, and exhaust gas velocity is still important even on a turbo car.

88 5 spd, K&N cone with CryO2 intake and IC sprayer, .48T-3 & GN comp whl, 3" exhaust, Dynomax Bullet & Ultraflow,
RR cam & Race Eng spkt, ported E6 & intakes, MSD 6A & coil, 8.5mm Aurora wires, RW crank pulley, Ranger clutch fan,
ARE 5 star whls, 235/55 Falcons, Tokico Ilumina adjustables, Eibach prokit springs, Energy Bushings, Frame connectors,
B&M shifter, Autometer boost on column and triple gauge pod in cubby hole.
Dreaming of header, alum driveshaft, NASH and SDS
Need; good clutch and motor mntsSmile
Grocery Getter/Rice Cooker.

Matt S Offline
Posting Freak
Cool thanks. I'd still like to make a trend if I could. I'm thinking a list how many people have done what to their car.
Anyone else? Or am I talking to Pete's barn door long distance... [Image: biggrin.gif]
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