OdessitPashka

I cut my cat off on Sunday in order to do some secret modifications to my exhaust and since everything was gonna be temporarily(sp?) I used some reducers and muffler clamps. Pipe before cat is 2" OD and pipe after cat is 2.25" OD, weird! So reducers that I got thinking we have 2" were not the right size, but it was Sun after 6pm and I had to put it all somewhat together and drive with it until today to finish it up. Well bumps on the road got the whole thing off and I was driving with exhaust manifold and half of my flex-pipe.

It was very very loud and the whole car was shaking, as well as I lost all the power in low range ( up to 3500rpm). It picked up in 1st and second at the top end very nicely, but in third gear I could bearely get up to 6k RPM. Car didn't pull at all!!!

For now I have a pipe instead of my cat and I feel all of my power back and high end is still very very nice( I think test pipe helped).

Well, my conclusion is that big exhaust(anything over 2.25" ID), which would be equivalent to kind of what I had, is overkill for our engines unless you are spraying or have a turbo.

AEMTIB01

i agree lol

Mad-Machine

some will tell you that you need "back pressure" for an exhaust to work.. that is not entirely true.. what you need is a "Scavanging effect" that having a well balanced and good flowing system will give you. In effect, the previous exhaust pulse will pull along the next and so on and so forth, not enough to make a vacuume, but enough that the resistance in the exhaust is reduced.

01tibby

^^^^yeah, its called pulse harmonization or something like that.

same reason some car manufacturers are looking into variable-length intake runners.

Double_A

So if your running low boost like 7-8 psi with a T3 or T3/T4, what would be the ideal exhaust setup?

OdessitPashka

2.5" should be plenty.

Double_A

So 2.5 with exhaust from wastegate included is ok?

Dweet

<div class='quotetop'>QUOTE (Speed-Factor)</div><div class='quotemain'>Yeah with a 7-8psi setup you will only need a 2.5", anything over 300whp you should be looking at 3".</div>
I dont necessarily agree just because in a few SSC issues various turbo projects they have done they have pushed up to 450hp with 2.5" exhaust

Double_A

wow i didnt realize you could run soo much power on such a small exhaust system. Thanks