I was just using a "for instance" example. Most engines get their best full-throttle power/performance at around 36-37 crankshaft degrees of advance at high RPM, (centrifugal only) and best gas mileage at light-throttle cruise with another 10 degrees or so of vacuum advance added on. As soon as load increases, such as pulling a hill or passing, the vacuum advance goes away- - - -it's just not there with even a moderate amount of load applied. Differences such as camshaft grind, type of transmission, intended use such as load-pulling versus quick throttle response, etc. all factor into an engineer's choice of a particular advance curve. The biggest mistake most folks make is getting too much advance too soon- - - -engines don't like trying to run backwards when too much spark advance gets dialed in.
A series of chassis dyno tests we did on the 1934 Ford coupe family race car with a flathead V8 back in the mid-1950's showed that the power loss from 1 degree too much advance at full throttle was the same as the loss from 5 degrees not enough advance. If you err on timing, too little is not as detrimental as too much!
Jerry
Last edited by Hotrod Lincoln; 11/14/2013 12:43 AM.
