Yep, it does retard on boost. Stuart at vmax explained to me in the end. On the super charged set up you set the advance to 24 degrees at 4000rpm. This sets the advance just right at idle.
Sorry for dragging this up (only stumbled over it just now while looking for something else).
I've seen this advice previously from this company regarding the use of Vacuum Advance Distributors in Boosted applications.
Be aware, some Distributors will retard when a Positive Pressure is applied to the Vacuum Advance.
A friend found this out after burning exhaust valves. He disconnected it, and apart from no longer having issues from burning valves, it actually went better.
Later, he had it run on a Rolling Road and had a distributor curved to suit and it goes considerably better.
Vacuum Advance Dizzy
Posted 25 January 2020 - 10:52 AM
Posted 25 October 2020 - 11:40 AM
I'll add my questions to this thread too,
I've got a sc12 charged 1098 and a 43d4 distributor (I think 41404? curve, morris marina or canadian mini) I set up a pointer on the timing case to help me with the strobe light. The car was running well and i put the timing light on and it said 12 deg advance. I retarded it a bit and settled on 10 deg at idle (800rpm) which gave 24 deg at 4000 rpm. I think this 24 deg will be ok, the dizzy has a 10 deg advance plate in it and does not have vac advance. I've been told that a supercharged engine doesn't need much total advance and i'm hoping that 24 will be ok. Stuart also advised that a vac advance should still be used though, but I can't understand why? is it for when you take your foot of the throttle and it's coasting along and advances the timing? is it for economy off boost? I don't know.
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