Sam,---re your request for info on timing related to RPM: It is reasonable to assume that as the RPM increases, the injection timing will precess to an earlier setting in a direct relationship to RPM. Say, at 600 RPM, the timing is set at 24 degrees Before Top Dead Center, and at 4200 RPM the timing should hypothetically be 50 degrees BTDC. At any point in between, the timing should be advanced proportionate to the amount of increase in RPM.

If baseline (idle RPM) is 600, and 4200 is redline, the RPM range is 3600. If the recommended advance increase is a total of 26 degrees ( remember it is a hypothetical number just now) for that RPM range, then the ratio is set and for every 1000 RPM increase, there will be a 7.22 degree increase in advance. ( or, a 3.61 degree increase for every 500 RPMs). At 1600 RPM, the advance would be 31.22 degrees. See how the relationship goes? I don't know what the recommended advance is for any RPM other than idle so I can't say what the increase should be for our engines.

I thought I read a specification re the timing at higher Rs but that number slid off my plate somewhere. Someone should be able to provide it. Maybe a friendly MB service manager. ( toss him a knockwurst and a beer) Maybe somewhere in a service manual.

Anyway, this is my take on the subject and with the supposition that it is a straight-line increase, anyone should be able to do the math once the advance is known for a specific higher RPM.

In an ignition gasoline engine, the ignition timing seems to follow a "curve" and that is adjusted for optimum performance under specific conditions at different RPMs in a high performance vehicle. Varying factors of volumetric efficiency according to design of intake passages, cam profile and exhaust effectiveness, among others, determine requirements of ignition timing. I'd guess that the factory specs have taken into account the lesser and varied performance requirements of the family grocery-getter and set the "curve" accordingly.


So, it is understood that a proper timing of ignition is a significant factor in optimum efficiency and the principle is not at all lost on diesels. Go for it, Mr. Duntov. Show me up here.

Sparky