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Old 04-16-2009, 01:19 PM
SteveH SteveH is offline
Hard Core 4+
 
Join Date: Aug 2006
Location: Colo Springs
Posts: 1,820
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Thanks for the info!

Actually, the 'ported vacuum' sent to the advance module gives you *more* advance at full throttle. (If you had accidentally connected 'manifold vacuum' to the advance module, you'd have full advance at idle, and none at full throttle').

A vacuum delay valve could be added to prevent sharp transitions that might cause transient preignition, but it since the vacuum would 'catch up' eventually through the VDV, it wouldn't solve chronic spark knock under a static condition (prolonged full throttle, for instance).

Perhaps we need a vacuum line with a wastegate ;-).

My understanding of a 2F dist. (or most of that era) is that the mechanical advance provides the bulk of the total spark advance (perhaps up to 30-some degrees) and the vacuum advance just adds a few more. With a timing light you can do some experimenting (at least on an engine with real markings, unlike a 2F) and learn a few things. I know that when the vac. advance plate was rusted tight on my '78 2F, it was a real dog. A few smacks with a hammer and screwdriver, and the rusted-stuck advance plate broke loose and freed up some horsepower.
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