Thread: Exhaust sizing...

This is 3" dp with exhaust disconnected. You can have a 4" exhaust for more flow but there is more to it than that. every bend in the pipe is going to change exhaust gas direction, which takes energy. This energy is represented by backpressure. On turbo cars, the less backpressure the better.

A 4" pipe will flow more and therefore have less backpressure, even throughout the bends in the pipe. No exhaust is best, so I say it would fit the car better if you went with a 3" exhaust and a cutout system. A 4" exhaust would be too tight of a fit on our cars. you would bottom it out all the time.

however theres no saying that 3'' isnt optimum for your setup. if you go with such a large exhaust, you can change the way your engine responds in boost, creating engine power later in the RPM, create more lag, it will always make more top end as thats where you are creating the most volume of air flow, however you may sacrafice your low end to mid range to get top end flow, i donno if thats 100% worth it. its kinda along the lines of choosing a AR larger you go later the spool, more top end,ect

With no exhaust I made more bottom end power, a lot more. Look at the graph. I made more power throughout the powerband. The turbo spools incredibly faster with no exhaust hooked up.

When it comes to turbo, bigger exhaust is always better. A smaller exhaust will never out-spool a bigger one, and will never make more power up top than a bigger exhaust.

I can go into why this is into more detail later.

Best exhaust evah for turbo cars:



NO EXHAUST.

I told you man...

Tekkie, this is the thread I like to toss around because I don't have to spend any more effort than just linking to it:

http://www.e30tech.com/forum/showthread.php?p=680504#post680504

Post #5 especially. Sorry it's on a BMW forum...



This happens to a small degree before the turbo but as Coheed said, the exhaust turbine ruins any change of pulse tuning or scavenging effect post-turbine. The best exhaust for low, mid and top end power on a turbo car is no exhaust.


Personally I wasn't expecting the 4" exhaust to ever come up on this forum. Apparently the VE+T engines are breaking new territory. I've worked a 4" exhaust before and I'll tell you, it did wonders for power delivery. Made a power record (U.S.) with one. Anything over 400 WHP could really benefit in my mind from a 4". Running it is the other issue. I'd look into a dump long and hard first before I decided to go 4" all the way...

This is incorrect.

Even on my old basic T25 setup, running open cutout the car felt like a whole different animal. The turbo is enough of a restriction. I'm not planing on waste any more money into exhaust. Just a 3" cutout replacing the cat (as a test pipe), with a 3" downpipe, and after the cutout the old 2.5" that i used to have from my N/A times, for a nice and quiet sound on daily use.

LOL, I got a 3" crush bent (JGY sux) downpipe, to a 3" exhaust cutout (replacing the cat as a test pipe), with a 2 1/4" exhaust.

Thanks that's just what I was looking for. I'll just stay with 3" piping and have the shop weld me in a cut-out for the track.