exhaust dummy..

[907DAVE]

Do a turbo back and be done with it.

The whole back-pressure idea is a gasser thing and does not apply to our diesels. The turbo can generate all the back-pressure you want.

[I Eat Catfish]

cool. That will give me an excuse to get a straight pipe.

[KT Performance]

The straight pipe is also your cheapest option.

[Power Hungry]

Originally Posted by 907dave

Do a turbo back and be done with it.

The whole back-pressure idea is a gasser thing and does not apply to our diesels. The turbo can generate all the back-pressure you want.

I beg to differ just a bit. I've personally dynoed a truck with a 3.5" downpipe and a 4" downpipe and under load lost about 25-30 ft/lbs below 1750 RPM running the 4"... making no other changes. Of course, the 4" flowed better in upper RPM ranges and power was better there as well as having lower EGTs. So there is some truth to the backpressure stuff.

[907DAVE]

In school we were doing dyno runs trying different combos on our three fiftys, and yes we did pick up around 6-10 hp's in the lower RPM ranges with mufflers on. But from there on they were causing a very slight loss in power.

Bill do you think the 4'' was actually creating more backpressure in the low R's because of turbulence or expansion in the down pipe(not sure on the technical term), and the 3.5'' actually had a smoother flow?

[Power Hungry]

I couldn't really say. I'm not big on fluid dynamics but if I had to venture a guess, it is very possible that could have the case. I know gassers backpressure is needed to help improve low RPM performance and I imagine there's a similar effect in the way the exhaust is discharged into the downpipe.

[tuckman]

Bill,

Could you write a tune that keeps the turbo veins closed a bit longer to get that lost power back, for owners that have the straight pipe? Or is that something that is already done in tow tunes?