Exhaust - Downpipe Diameter

[Sarasota]

I heard recently that a smaller downpipe will allow the turbo to spool up quicker at lower RPMs - however, a larger downpipe will reduce backpressure. What are your opinions? I'm fixin to spend some Christmas money on a system.

[vitalidle]

My 2 cents get a 4 inch downpipe all the way back to the tailpipe so you can lower your egt's if you choose to get a chip or tuner down the road.

[silverF250]

Don't put a smaller one on because if you do add a chip your egt's will go through the roof.

[cvdenson]

I agree get the 4". For a long time I had the stock exhaust straight piped and put in a 3.5" down pipe. When I switched to the 4" system, I noticed further EGT drop (25-50 degrees at highway speed) and faster turbo spool up.

Chris

Originally Posted by silverF250

Don't put a smaller one on because if you do add a chip your egt's will go through the roof.

You definatly dont want smaller than stock, but believe it or not a 3" dp (stock) will flow enough for 600rwhp. How do i know??? I made nearly 600rwhp on my obs truck with a 3" dp on fuel only and well over 600 on spray. FWIW I run a 3.5" dp on the superduty, it is the only option with the aftermarket turbo.

[strokin_early_99]

I run the same turbo mounting system as Luke however I do not make the power that Luke makes.

[silverF250]

Yeah I know that they will flow enough for big power, but what were the egt's at those levels on a 3" downpipe. Just wondering. I read it as he was going to go smaller than stock, and IMO that would be a mistake.