Quote:
Originally Posted by Jack Shaft
I've found advance stays the same,1 degree per 100 rpm with a 7 to 1 head,which is the upper limit for a model a head due to flow reduction. There were some problems noted by some people with the FSI advancing a little too far at peak,a few degrees over the 1 per 100 threshold..I don't find that with mine.What does happen when increasing compression is that the engines tolerance for timing deviation lessens,dont run a high compression head with manual advance. 4.2 to 1 is tolerant of timing flaw,you can set one fixed timing and drive..7 to 1 will hammer on you,with a bigger hammer than 4.2 to 1..
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That all makes perfect sense. My engine is at about 7.0-7.5:1. It started at 5.5:1 but the head has been off a few times and each time, I make it flat again before refitting. Over the years, the CR has crept up to what I think is the limit. I have been considering doing what you say not to do - go back to manual timing because getting it right with auto advance is too difficult without the equipment to test the dizzy.