January 12th, 2008.
Gentlemen:
On the subject of back pressure vs. noise reduction, permit me to weight in with some of my experiences. A gentleman I knew had an ex-Louisville & Nashville Railroad office car that he refitted with a 60KW
generator set driven by a Perkins diesel engine. Unfortunately he failed to calculate the back pressure on 50' of tailpipe to the end of the car and up to the roof. The result? Burned out exhaust valves and inefficient operation.
Some marine and railroad diesel engines were designed historically to use a drum type exhaust manifold on top of the engine, and the firing order was so arranged that exhaust impulses from two different cylinders would be emitted into opposite ends of the drum at the same instant, with the exhaust stack in the middle and of sufficient diamter to handle venting the exhaust with little or no back pressure. The Result? Noise reduction with minimal back pressure resistance due to the pulses just about cancelling each other out almost completely. The principal is the same as white noise of the same range from an opposite direction cancelling out the original noise source.
Unfortunately for us, the LDT465 and the normally aspirated versions do not seem to admit of much restriction in the exhaust system before a price is paid in reduced efficiency and power output, as the firing order and exhaust collector systems seem to be set in stone in regards to their design specifications. Perhaps a reengineered exhaust system, or a power plant and transmission replacement with a more modern unit would be in order to achieve the goals of making these trucks more user and dare I say it, environmentally friendly.
Apparently according to Mr. Doyle, the Army tried to get permission in the late 80's or early '90's to mnufacture several thousand new engines for these trucks, and the EPA didn't buyit, hence the gradual replacement of the G-742 series trucks in the Army inventory. I appreciate the concern for the environment as beingof necessary importance, but if these were Tactical Trucks, I might point out that a war is pretty hard on the environment too-
! Look at how dernier a resort downtown Bagdad has become lately, but then it probably could stand some urban renewal (B-52's do come to mind). In any case I will keep an eye out as to how you gentlemen resolve the question as it is quite pertinent to the operation and possibly the preservation of our trucks.
Thanks Again,
I remain, Sincerely,
Kyle F. McGrogan
1963 Mercedes Benz S404.114 Unimog (Swiss)
1971 KAiser Jeep M35A2 Wo/W "Saddam's Nightmare" Vietnam and Desert Storm Verteran Deuce.
