exhaust size piping question????

[chillmieste]

I have a s13 red top motor with a t3 turbo setup. Im doing the downpipe and exhaust in a couple of days and I really need help with this. I was told from a guy that if I go with 2 1/2 in piping I will get very little boost lag. I was planning on going 3 inch but why put 3 inch if your gonna get more lag???

[crzycav86]

How much boost are you running?

From my limited knowledge, go with the largest piping that will fit under your car....

[Cyberkreig]

i dont know how backpressure would reduce lag?? maybe there is something i am missing..

[C-Kwik]

What is your piping size now? 2.5 inches will give you better flow than a smaller pipe. But bigger than 2.5 is probably going to be better.

Turbos work a lot off of the pressure differential. Say if there is 5 psi in the exhaust and to reach a particular boost level at a given RPM, you need a 10 psi differential across the turbine. Then the exhaust manifold pressure will need to be 15 psi. If you lower the exhaust pressure to say...a more reasonable 2 psi, then the manifold pressure will only need to be 12 psi. This will free up some extra power.

As far as lag, it will feel more powerful at less boost, and the motor will not have to build as much pressure in the manifold to create the pressure differential needed to produce the desired boost.

[Phax]

3inch piping flows more air, which means you make more power at the high end. How much boost are you planning on running? If it gives you any comparision, I have a 3inch downpipe coming off of my stock T25 and I get full boost by 3000 RPM.

[chillmieste]

IM running without an intercooler right now but plan on going front mount in a couple of months(dont make much money). I have a t3 but i plan on running higher boost after I get the front mount. So about now im gonna try and push 10lbs of boost until I have enough for the front mount. I should just call my mechanic now and tell him 3 inch. Im better off doing that in the longrun right????

P.S. Thanks for all your opinions and help

[Phax]

IM running without an intercooler right now but plan on going front mount in a couple of months(dont make much money). I have a t3 but i plan on running higher boost after I get the front mount. So about now im gonna try and push 10lbs of boost until I have enough for the front mount. I should just call my mechanic now and tell him 3 inch. Im better off doing that in the longrun right????

P.S. Thanks for all your opinions and help

Hang on, lemee get this straight. You're planning on running 10 pounds of boost, with no-intercooler on a stock fuel system?

Do you have another SR in the garage to drop into your car when you blow your current one up?

The convential wisdom is that the stock fuel system is taxed at 8psi. That's with a SMIC.

I think that you need to rethink what you think you're doing with your car. At the very least, get an EGT gauge to keep an eye on the exhaust temperature. It would really suck to melt a piston before you even got the FMIC.

[chillmieste]

would I be ok at 7psi then?

[Cyberkreig]

I would keep the psi as low as possible until you can get an intercooler of some kind.

[rco8786]

I don't even think I'd drive my car w/o ANY intercooler...what happened to your side mount?

[implict]

Go 3 " all the way and also do the sr a favor.... get an intercooler of somesort.

[chillmieste]

I got a good price on it 1000 for motor transmission (head port and polished, cam gears, and greddy head gasket) Not gonna pass up that deal. The engine was missing the intercooler and a/c compressor. It had everything else. I called my mechanic today and said just to go 3 in all the way. Thanks everyone.