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Weird one:
On my racing project, I'm using a Model 50 alternator engine (as that was an engine I could get my hands on). But, I'm going to use an SR1 magneto, as ignition should be period for that racing club.
Magneto engines should be timed at 11/16 degrees BTDC, but alternator ones at 15/32 degrees BTDC. I was inclined to use 11/16 as I'm using a magneto now and thought the different timing might have something to do with differences between magneto and alternator and somesort of delay in one or the other.
However, I vaguely remember earlier engines have 7" conrods, while the later ones have 6,5"? Mine's definitely the latter. So could that be the reason and should I use 15/32 degrees BTDC timing?
Degrees or inches?
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There would be no difference in ignition timing between magneto or coil ignition all other things being equal. A different con rod length would have minimal effect on the geometry either.
A quoted difference in ignition timing is most likely due to other factors - cams and compression ratio being the more likely causes. Or a misprint.