3" exhaust really necessary for FI ?
 

Simple question: how much impact does the 3" exhaust provide for moderate power FI system versus the typical 2.5" ?

Is it necessary? No. Will there be a difference? Yes. Largely depends on the design and output you will be at.

Enough to make it worth going 3" if its your first time around buying exhaust for the car.

If you already have a 2.5" system stick with it until you hit about the 350rwhp mark.

For a turbo system, the exhaust closest to the turbo is where it matters most, the closer towards the exhaust tip you get, the less of a difference a larger diameter exhaust will make.

you do realize that if you have a 3" down pipe 2.5" Mid and 3" exhaust the entire system will flow like a 2.5" system

The " A chain is only as strong as its weakest link " doesn't apply to exhaust in terms if diameter.

3" from the turbo that tapers to 2.5 at the frontpipe and remains that size to the end will perform better than full 2.5 from the turbo all the way back.

Its a matter of back pressure. JDL's car made 416rwhp at 16 with a 3" downpipe to 2.5 exhaust. He would of made less and spooled slower with a full 2.5" system.

My objective with forced induction is a heat manageable 275 whp that will stay reliable for 6-10 track weekends a year and some rotational daily driving in between. My orginal plan was leaning towards a turbo system sometime next year but something came up that may put a supercharger on it much sooner. I was planning to buy an ISIS catback because I love the sound and the price but if a 3" makes sense then I will probably by the Ultimate Racing version for the same reasons. There is still the possibility that the car will remain NA and I have heard all kinds of talk regarding compatabilty with a 3"exhaust. If the s/c deal moves forward then I am limited to just a catback for the time being. Meanwhile I have wheels, tires and suspension parts stacked up in my garage and guest bedroom waiting for me to get to it. I have only had one chance to get it on a track(Roebling) so far in stock form and although it wasn't exactly fast it was a blast till the tires cooked and it has lots of raw potential. Sucks though having to honk your horn to get another driver to lift a little after they point you by.

http://i40.tinypic.com/30tsxg8.jpg

I'm going full 3" N/A for a while before I go turbo. I don't feel like replacing the entire exhaust for when I do go turbo later down the road. The sound I don't have an issue with as I will be keeping my front pipe catted, a beefy midpipe resonator and my Nameless offset axleback. The turbo will quiet things down later.

I made the same choice and ordered the Ultimate Racing 3" this week. I don't expect any downside if the car remains NA longer than I expect.

I'm contemplating getting the new 3" perrin due to wanting fi after the warranty goes out (and I have a better job). I currently have motivs over/midpipe combo catted. Do I have anything to worry about running this for a while?

I don't see why not, although I'd probably recommend something more than the stock header when running a 3". I could be wrong though. I doubt you will see anything negative.

3" is overkill plain and simple unless you're 500+ HP.

I'm going to be picking up a 3" system soon, but for now I'm running the stock exhaust with my turbo. It's still fun as hell. I'm sure it'll be better with the 3", but I wouldn't say it's a prerequisite for boost. Even a 2.5" I'm sure would be fine for most reasonable boosted applications, and probably a bit quieter.

This statement is based on what facts?

Have you ever felt the difference between a 2.5" and 3" exhaust on the same turbo car?


TURBOS LOVE TO BREATHE. FACT.

Bigger the better on a turbo car. Open downpipe if you can swing it. SC/NA is different though.