[Vwdiesel] Muffler or Streight pipe

[LBaird119 at aol.com]

In a message dated 12/9/2009 3:06:17 PM Pacific Standard Time, 
toensing at wildblue.net writes:

> I wonder if replacing the muffler with a straight pipe on VW &Mercedes 
> turbodiesels would significantly improve MPG? Also, does the turbo quiet the 
> engine enough to be legal? I suspect someone out there has experimented 
> with this. I also know that some engines have tuned exhausts &that decreased 
> or increased back pressure could decrease MPG.

  A gas engine needs backpressure to keep the air fuel mix in the 
cylinder during valve overlap.  A diesel has no mixture so a little 
leakage on overlap will do very little other than slightly less O2 
but also less, leftover exhaust in the chamber.
  With the turbo, a 2.5" exhaust will do wonders.  It varies how much
it will do "out of the box" though.  Sometimes it wakes it right up, 
other times you really have to take advantage of the much cooler 
EGT's and crank up the fueling.  Bringing the EGT back up will add a 
noticeable amount of power and either maintain the MPG or improve 
it a couple.
  As I understand it, the exhaust ends up pretty quiet, until you romp 
on it.  Not bad but most likely louder than I'd like.  I lean toward a 
low restriction muffler that'll quiet it down.
   Yeah Tad, I put a flowmaster on the 4KQ.  Sounded kinda nice 
but a tad loud when you got on it, otherwise it was kinda hollow 
and raspy sounding.  They sound better on a V-8!
     Loren