[Vwdiesel] Muffler or Streight pipe

[William J Toensing]

Here is something that might make for an interesting discussion. I used to own an Argosy (Airstream)motorhome that the previous owner had installed an Isuzu 6 cylinder industrial turbodiesel. The engine had no muffler, only a straight pipe. I was told that the turbo reduced the noise level enough to be legal & with no muffler, would get better MPG. I wished I had kept it as at times, it got 17 MPG! This on a 26 foot motorhome on a 1&1/2 ton Chevy chassis with a THM 400 Hydromatic plus a Gear Vendors  gear spliter. But my wife didn't like the noise.
Become of my prior experience with the Argosy, 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. The Panhard PL-17 was one such car.
Bill Toensing, Nevada City, CA.