Bird, picked up that information from the Cummins web site. It makes sense to me that it is at the very least very close to that with perhaps some variation to allow for temperature and quite possibly other situations. The reason for this formula was that it is what is required to burn each unit of gas precisely and without adding to emmisions. To much air and the lean mixture will overheat a gas engine in no time, to much gas and you could'nt get your car through a California smog check no matter what computer your running. Carburators were notorious for varying the amount of fuel as various parts got worn and the older generation fuel injection, especially the GM throttle bodies (which weren't bad but don't have a snow balls chance of meeting the latest EPA demands here in CA,) had less ability to detect the correct adjustments required for given conditions. I do believe you are correct that the amount varies, but I'll bet its very small, perhaps by a point or two. Diesel varies from as high as 100 to 1 all the way down to about 33 to 1. As you know though, with a diesel, if you add to much fuel, your exhaust gases get hotter with the increase in fuel/load, to the point that damage will occur. Its why truckers use EGT gauges to keep the temperature of the exhaust at a reasonable level. I believe anything much over 1300 degress is to be avoided. My Ford will get the gases up to +1200 degrees when climbing the Donner summit up near Lake Tahoe. I think one of the reasons is the thin air will not allow full combustion and unburnt fuel is allowed in the exhaust system where it will continue to burn creating the higher temps. Rat...
