exhaust setup - 3" or 2.5"?

rk4g63 · 10-13-2005

Tech Question :
My setup is 94 talon tsi awd, big 16g, 2.5" homemade exhaust, Supra TT smic, evo 3 manif, stock 1g 7 bolt. I don't want to mess with porting the turbo or anything like that all. I'd rather avoid pulling anything apart unless I break something.

If I go with a 3" exhaust could it cause boost creep? If so, why? Could it be because of not enough backpressure?
Apart from the corrosion factor, does stainless steel add any extra performance in terms of heat dissipation, etc?

**Shane@DBPerformance** · 10-13-2005

You aren't going to see much for gains going from a 2.5" to 3" exhaust with your turbo.

The 3" exhaust could cause boost creep, because it will flow the exhaust easier. With more flow, the wastegate portion might not be able to keep up and it could be easier for some of the exhaust to go through the turbine wheel, instead of out the wastegate, causing it to make more boost. You will probably lose some part throttle, low load torque feel, when you goto the bigger exhaust. At WOT, it should gain a little torque, spoolup and an HP, but when you take off slowly from a stoplight, it might feel a slight bit weaker.

Stainless steel is good at keeping heat in, which is what you want with an exhaust. Most of the cheaper steel exhaust also have some sort of coating on them though to prevent rust and help keep heat in. Stainless exhausts are usually a tad bit lighter than cheaper normal steel exhausts.

rk4g63 · 10-13-2005

Basically, I want faster stoplight takeoffs and faster1/4 mile times and yet not have to mod more than what I have (original post) and am planning now (650 cc, chip, 2g maf, safc2). You know my setup pretty well (at least the projected one). Do you think I should stick with the 2.5" I have, or change over to 2.5" stainless? Or would the 3" SS be better?

**Shane@DBPerformance** · 10-13-2005

It isn't going to make much of a difference. On a car putting down around 350whp, you might gain only 5 whp by going from a 2.5" exhaust to a 3" exhaust. On a car making 300whp or less, it might hard to even see a power gain, unless you do magazine style dyno runs.

I would wait until your current one falls apart or you go with a bigger turbo.

rk4g63 · 10-13-2005

Thanks Shane. I'll just wait. Saved me some cash!

I don't intend going over 300whp. That's about all I want - just crossing 300 whp is fine with me, but not at the cost of engine & tranny reliability.

Thanks!

Jakey · 10-13-2005

RK when JET gets my 2.5"-3" SS downpipe & 3" SS cat-back done I'll give you my $0.02 on how it feels compared to stock. My O2 housing will be stock for the time being though.

**Halon** · 10-13-2005

Just for the record, RK's 2.5" is not mandrel bent, it's press bent. With that being said, I would think going with a 3" mandrel bent system would be a nice upgrade.

**Shane@DBPerformance** · 10-13-2005

Yea, press bent sucks and usually sounds bad also.

A//// Guy · 10-13-2005

Back when I had my pressbent Burshur system it sounded great, althought it was super loud. Then I went with a nice custom quiet 3" mandrel and that was perfect.

Jakey · 10-13-2005

You could always forgot about 3" and to to 3.5" or 4 inch.

**Kracka** · 10-13-2005

Quote:

Originally Posted by Jakey

My O2 housing will be stock for the time being though.

Jakey <3 boost creep