As mentioned, diesels don't need backpressure.

But neither do gas engines. What they need is "flow velocity", which is associated with smaller plumbing (ports, runners, etc).

With even a slightly larger cam, a gas engine gets more of its intake suction from the exhaust gasses leaving out the port-- much less than the actual downward motion of the piston. So if you want your gas engine to perform well, you need to maintain exhaust escape velocity as well as intake velocity.

This is the same reason many people see good improvements with a 4" exhaust on a CTD, but not with a 5". In simple terms, the 5" is too big and allows the flow of exhaust to stagnate in the pipe, increasing the energy required to "push" it out the pipe by overcoming atmospheric pressure.

If you really want to reduce backpressure, locate the exhaust pipe exit in a very low pressure area in the truck's slipstream-- oriented like a Pitot Tube it will cut backpressure.

Justin

 

Two major differences with diesels and gasers.

Gas needs backpressure and engine builds vacuum
Diesels do not.

 

Hmmmmmmm, I thought I must have been missing something as to why my HP numbers were down a little.
(now purchasing two large potatoes, one to stuff in each stack to get the back pressure up)

Wonder what this guy would tell your mechanic about back pressure?

http://rides.webshots.com/photo/1181...58682169SCJtTI

 

Yea the last time a mechanic told me that cummins was owned by Ford and that cummins have glow plug's. yea that was the last time i saw him. I would go find another mechanic.

 

So does that mean scavenging doesn't apply to a N/A diesel?