3" Downpipe, 3" Hi-flow cat, 2.5" cat-back???

[Cool Mr Steve]

Ok, with the setup in the title, how much is the 2.5" cat-back going to kill me? I have a 2.5" cat-back on the car now, with a 3" downpipe and cat on the way, but is it horrible that it is going to have to neck down to 2.5"? BTW, telling me that my exhaust should go from smaller pipe diameters to bigger is not going to help my situation...

 

[IansRedTalon]

Going from smaller to bigger on a turbo car is a moot point. The way the exhaust pulses exit a NA car are much different then the way the exhaust exits on a turbocharged vehicle. On a turbocharged car, the turbine acts like a fan.
What this does is it takes the exhaust pulses and turns them into a constant flow of exhaust gas. This is the reason why going as big as possible after the turbo is a good thing. The fast the exhaust exits the turbine the less pressure acts against the exhaust pulses coming into the turbine housing from the exhaust manifold. This means faster spool up.

Going from a 3" to a 2.5", you will possibly lose a minute amount of power over running 3 inch the whole way back. However unless you are in a highly modified car the difference should not be noticable at all. However the farther along you move with your mods, the bigger you will want to make the rear section of the exhaust.

Ian

 

[leet]

You should be fine with a minimally modded setup. If you ever decide to purchase a turbo that flows more, you will probably need to alleviate that restriction. For now, you'll be alright.

Here's some good feedback for you IRT.

 

[yunior]

it al depends on how much power your looking for if your looking to go 400 and over then go with something larger 3" or larger like the other guys said if you want something just for messing around in the streets keep it the way it is.

 

[Cool Mr Steve]

I've also got a Big 16g turbo I'm planning on putting on with that setup. It'll probably see a max of 17-18psi, so will the setup above work well enough for that amount of airflow?

 

[pboglio]

3" catback is worth about 10-15 h.p. over a 2.5" catback exhaust in the 300-350 h.p. range. I'd never by a 2.5" exhaust again, waste of money.