What would be ideal for the little l15a, 2.5" or 3"?

 

i would say 2.5 would be enough unless your planning on crazy amounts of boost

 

for max power and efficiency, 3" is best. you want almost no backpressure on turbo setups. and dont worry about noise, the turbo acts as a huge resonator reducing a lot of exhaust noise. You also dont know when u'll want to turn up boost . and believe me, you will.

For best exhaust and the best price, go custom. 3" piping (kteller.com), apexi ws 3" turbo muffler, and a resonator should you want it quieter later on. Kteller piping is the one best piping i've seen, its very tough even against speed bumps/scrapes. a good shop can fabricate it nicely.

 

Id suggest 2.5in.

 

you will be fine with 2.5. But tell us about your plans. what size turbo are you going to run? how much boost? etc..

 

I plan to use either a t25 from nissans or a td04 from a wrx. Boost would be about 10 psi.

@ 03dsm-rsx, yup turbo setups sound a lot quiter than the n/a tuned guys
So 3" hmm.

 

3" would yield higher HP at lower boost, also a beefier midrange.

less restriction is always better.

 

would large piping reduce the velocity of the exhaust gas? or does this not matter much on turboed cars

 

with ANY setup, bigger will always yield higher HP. HOWEVER, this only is true with the aid of ECU tuning to add the necessary fuel in the leaned points. With no such tool out for the L15, you will not see best gains. However, i'm using the emanage ultimate on my brother's scion and i saw a map for the L15. if u're really pressing for HP, ultimate is a very good tuning system.

3" + tuning = more torque than before
3" alone = less torque

The motor is really an air pump, put in as much air as possible and out. But another factor to consider on a N/A car is the streetability of a 3" b/c it will be loud.

i've heard quiet 3" setups before with the use of magnaflow resonators and apexi ws turbo muffler.

 

thats my setup! strong as a rock! or is it tough as a rock? u get the idea

 

On my turbo GTI, a 1.8l, the 2.5 inch turbo back will spool up quicker and more back pressure will give more low end mid power. The full 3 inch turbo back gave me more of a mid to top end power. Takes alittle longer for the turbo to spool up with a three inch, imo. Back pressure is everything in turbo cars! Your turbo depends on it! So in ending it depends on what you want out of your car.

Da Fitz....

 

sorry buddy but this is wrong. Backpressure works against the turbo, making it harder to spin and spool. 3" setup will spool up quicker than a 2.5".

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp or less, 2.5" is fine for the Fit. 3" would bring the power sooner, but probably wont net any higher HP.

 

depends alot on the turbo as well. Smaller piping can sometimes allow for greater exhaust gas velocity which can be better than bigger piping. On my JDM Nissan Pulsar GTiR I'm running a 2.5" downpipe off my GT2871R turbo then 3" after the highflow cat. I'm spooling way down at 2600Rpm compared to another person with a nearly indetical setup running a 3" downpipe who starts spooling at 3100.

Depends on smoothness of bends and velocity more I would think. I'm running over 360Hp at the crank and have no EGT issues,

with a 1.5L engine 2.5 would be enough for anything short of a fully build drag motor.

 

With the 1.5L motor and a small turbo like a T25, a 2.5 inch exhaust is plenty big. A 3 inch is too much for something that small and only running 10 psi. A stock STi has a 2.5L motor and is a 300hp car and has a 2.5 inch exhaust stock. I had a full 3 inch when I had 500whp at about 29psi. So with that said go 2.5 inch.

 

Alot of variables. From my experience with my turbo car w/ proper ecu tuning on a stock turbo....2.5 inch turbo back exhaust is better off the line till mid range. The 3 inch took alittle longer to spool but once it caught up my top end pulling abilities were ten times better then the 2.5 inch turbo back.
Now another option is installing a 2.5 inch downpipe going into a 3 inch exhaust system or vice versa. It all depends on what you are looking for in your car. Again this is all from my experience in having turbo cars.

Da Fitz..

 

Yea well im going to pull off something thats never been done before with a Fit and that is a STS System. :P supposedly no lag and the turbo stays cooler. I am going to be running a GT3271R Turbo from Garrett, seeing the '09 has yet to come out with any performance parts I have to build this turbo kit myself. I plan to spend around $4500 on this with a tune to 6PSI for DD and 12PSI for overtaking or racing, at least until I save up the money for a K20. Yea your saying with that money I can just do the swap but its going to cost a bit more with the tranny swap from a AT - MT. :/ I just want to have a little fun with my stock engine and see the look on the dumb@$$ high school kids faces when I blow past them and look in the mirror and see them struggle to catch up. Ahhh yea, I hate them. They ruin every meet spot we go to, always burning out and speeding through the parking lot. *Facepalm*