Digging up this old thread, which should've been in the how-to section.
The link to the geocities site on the first page is the first one I did, then I moved it to freewebs so I could post pix with the articles.
And, another article, bumping up the timing:
http://www.thedieselgarage.com/forums/s ... php?t=6041
To explain the fuel usage a little better. It takes an engine a certain cc's to get to, say 210hp at 2500rpm. If you make more power at a lower rpm, you acually use a few less cc's of fuel. On a low power engine, the engine is winding up to max rpm and staying there longer before the next gear shifts. A big reason why a 500hp 15 liter truck engine can get 6 mpg. The biggest factors in a bus would be; hp level, timing, gearing(trans and rear end), and the fateful aerodynamics. I thought about making a new how-to article that had all this stuff in it, but I'll need to take more pix or a video to really bring it home.