do straights reduce mpgs???

yeah, exaust system works with resonance effect to let exaust gas flow better and that's why straights may reduce boost pressure

 

the turbo on any diesel provides all the backpressure that will ever be needed.

 

I can't think of any situation engine related where back pressure is a good thing... Reducing back pressure should not decrease fuel mileage...

 

One theory is that no muffler = cooler exhaust temperatures. The cooler the air is becomes more dense and harder to push. I don't know if it is true. It may be that your ecm needs time do adjust.

 

Wouldn't less back pressure mean faster exhaust flow, leading to more boost? I could swear I gained a few PSI, maybe it's my imagination though.

 

I say who cares...it sounds cool, isn't that all the convincing you'd need?

 

going to straight full flow muffler, helped my m.p. & more power

 

What truck, engine? Does it have a wastegate?
First, read this little snipit from a repuatable diesel turbo company. It's main market is the smaller size rigs, but the theories are identical to the big rigz.
http://www.bankspower.com/techarticles/show/15-How-a-Turbo-Wastegate-Works
The first part will tell what you are likely experiencing.

I would not worry about the exhaust resinator theory IMO. It is a harmonic reducer more than a flow enhancer. In a forced induction engine as most all diesels are today, a long enough exhaust pipe on the cold side of the turbine is more important. When you shut the engine off, you dont want cold air rushing in against the turbine untill it has a chance to cool completely at a slow, controlled rate.