Posted by Dave in CA [172.68.47.45] on Thursday, June 07, 2018 at 13:04:28 :
In Reply to: Ingition Timing posted by Dlar688 [172.68.132.122] on Tuesday, June 05, 2018 at 19:03:49 :
In the old days, hot rodders would “power tune” to set ignition timing. Essentially, they would keep advancing the timing until it pinged, and then retard it a couple degrees from that and lock it down. If you’re lucky, the resulting initial + centrifugal advance (total mechanical advance) was in the range in which your engine made the most power at wide open throttle (WOT). For my 1970 Plymouth 340, the total mechanical advance at WOT should be about 34 to 36 degrees. I found that setting the initial advance at 10 degrees, combined with 25 degrees centrifugal gave me 35 degrees total at WOT. If I ran more advance than that, it would ping under hard load. Yes, I realize that a flathead six and my engine are very different. That said, here’s the main point I wanted to make, and there is something directly applicable to any engine. If I ran higher octane fuel or significantly less advance, my engine would run hot. In other words, running too little advance for the octane of the fuel you are burning results in combustion that continues beyond the point at which this energy can be converted to power. The remaining combustion process results in energy that is simply converted to heat, resulting in an engine which runs hotter and gets fewer miles per gallon than it could have with optimal timing. I don’t know the optimal total mechanical advance at WOT for a 230 or 251 flathead six, but I think that would be a starting point for determining the optimal initial advance and octane requirements.