Im going to be redoing my exhaust setup soon, and I was wondering if I'll benefit from a 4" downpipe at all. Im going to have all 3 inch exhaust, but Im not sure if there are any gains or if its pretty much useless. Any input's appreciated!

 

How big is the turbo? Do you actually flow enough air that you still have that much backpressure? There are people on here that run without any of that hoopla'. IE No exhaust.

 

its a t3/t04e turbo. I run 18lbs usually for race, and just 10-12 daily.

 

i think the 3in should be enough. I run a T4 60-1 and the 3in is big enough for it.

 

on a turbo car do u have to be concerned with the velocity of the exhaust gas after the turbo?

 

I dont know why you go from a 4" pipe and then step down to a 3" pipe. A 3" downpipe is fine.

 

3" is ok for you. In an ideal world you could reap benefits from the 4", but I doubt you could make use of any power gains with that t3/t4. Ideal exhaust for a turbo is......no exhaust! So basically, the bigger you go gives the biggest pressure differential, which gives greatest power. As mentioned above you want to keep velocity up...by the time your exhaust would come out your tailpipe with a full 4" back exhaust it would have cooled tremendously...probably causing more backpressure then a 3" (just a guess). In any case, I dont think anyone is gonna go full 4"....and going with just a 4" to 3" won't get you to the grocery store faster. On the track, I wouldn't hesitate to run a 4" _shorty_!

 

Back pressure is good because it keeps the torque down around a reasonable rpm. Unless you like having a really peaky powerband.

 

I don't think I understand what you are trying to state here. Care to elaborate?

 

Not. Back-pressure is good for turbos? Ok, you can run a 1" exhaust....thats much more back pressure then 3". If you want restriction for low end torque, you're gonna hurt your top end...so you STILL have peaky, but in reverse. I'd rather have my peak when I'm actually making power. You'll basically have the reverse curve...we will be peaking at 400 hp, you'll be peaking at 43hp.


[Modified by true, 12:27 AM 12/26/2002]

 

holy ****!!!...4"???? Does that even clear the oil pan?

 

I had a 4" downpipe on our race car last season, you should've seen it. It just looked silly! It went under the oil pan and had a dump shortly thereafter. It sounded pretty cool too!

 

on a turbo car? are u sure about this?

 

Tony can you run the exhaust after the oil pan and jsut dump it under the car. I was under the inpression that it must exit the body line. If i can do taht it would be great and alot easier to make a dp. My radius arms get in the way so id have to go really low.