zer0

Exhaust cutouts for everyone!!!

OuterHeaven

In a stock Turbo car the compression ratio is very low (which is usually a mistake by car manufactures). Anyways The reason those cars want a big 3" exhaust is because they want a bigger pressure difference between each side of the turbo at any given RPM, therefore making it easier for the turbo to spool up (making more power) and making the turbo spool at lower RPM (reduces Lag). In a stock NA car the compression ratio is higher and the car can make the pressure build up on the hotter side of the turbo faster which makes a 3" exhaust less of an improvement over a 2.5" exhaust. So much so that other factors like exhaust velocity can start to become more of an effect on power then the bigger size piping but I still believe that 3” piping would be better but it might be possible there would be a power loss in the mid-range RPM due to the lower volume of exhaust gases but I bet the peak HP would increase at least a little with a 3” exhaust on our cars.

zer0

^Absolutely correct. 30+ hp gains are possible.

Souljah347

thats not true, they don't want backpressure, they just don't want too lose velocity which would happen with a larger pipe. run open header and you'll see better results then if you bolted on an exhaust

tCUZZ

Hmm if I own a company that produce and sell 2.5" exhuast kit, I would favor the 2.5" over the 3". Make sense to me. .

jam0321

keep an eye out for a 3" downpipe back coming from G Spec and Strommung Exhaust. Strommung is a HUGE manufactorer of Subie 3" and larger exhaust and he will be making a 3" for the tC and sold through GSpec.com. Still waiting for final production and numbers. But there will be one available for all of you who need or want higher HP

06SuperWhite_SoCal_tC

And at the same time, Performance Companies make products that Perform. They don't make a exhaust to make your car slower/perform any worse... Like he stated 2.5" exhaust is able to support 400whp. But then again who knows im sure if a proper system was made you would see results with a 3" system too.

Joe_Dezod

You are correct. The idea is to flow as much CFM as possible with the least amount of temperature drop. The main causes to exhaust "pressure" is from either poor design (improper bends or inconsistent diameters) causing turbulence, or from colder exhaust temperatures (it cools down, becomes more dense, and doesn't flow as well).

Open dumps perform best because you have no pipe there to actually limit flow. A good exhaust design will actually "scavenge" the exhaust, basically pulling air out of the motor. This is where efficiency comes in to play.

A WELL designed 2.5" exhaust will out perform a regular 3" any day of the week. If you're running 14psi or higher, then a larger exhaust may be necessary. We'll be proving that our little 2.5" packs a punch though when we release our race motors.

tCing_U

^^Im saving for that race motor baby! woohooo!

enriquetc

ZPi, it is NOT impossible to run a 3" over your front crossmember, I have a mandrel bent 3" and it fits fine and is ran the same way as the stock exhaust was