Re: Bubba's chevy conversion dist.
Our latest conversions are shipped with 16 degrees (engine) of mechanical advance ( may be adjusted up or down with allen screw). The vacuum cans as supplied usually are 10-12 degrees of additional advance with full manifold vacuum applied and may also have the rate adjusted as to when that may happen.
Assuming the engine timing is set on the mark at 2-4 degrees btdc ( idle with no vacuum on vac advance) The engine when reved up ( 2500) would add another 16 degrees at 2500 rpm. This is with no vacuum.
Now lets add the vac unit to the deal with manifold vacuum applied. The engine would start with the 2-4 intial set on the pointer and when the engine starts the vac will add the 10-12 degrees giving the engine approx 16 degrees . (at idle) Now lets rev up the engine , when the engine is reved up the vacuum will drop and the mechanical advance witll increase . ( you wont have max vacuum with 2500 rpm or engine load).
This will allow the vac and mechanical advance to over lap each other to maintain a constant 16 degrees all the time the engine is running.
Both can be tuned to make this overlap perfect. Richard in Fla has mastered this adjustment with many trial and error drive sessions etc....
Clear as mud right ??? :>)
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