Dogwater wrote:Chevy 357 ci gen1, ported Vortec heads 062's, regular HEI dist, Edelbrock Performer intake for Vortec's, Edelbrock 750 carb. (1407) CR 9.8. Just played with the timing yesterday, installed a MSD vacuum advance stop plate, doesn't advance anymore than 10° now. Mechinal advance stops at 10° also with 12° initial for 32° at idle. Vac advance is connected to the ported side. Rev it up to 2500-3000 I get 51° w/vac adv. connected. Went for a drive in this 98° Texas heat an It drove surprisedly well, responsed well, I was surprises as well!! I'm just a bit worried but not to much about 51° total. Should it be lower?
Part of this problem is terminology.
"Total advance" DOES NOT INCLUDE VACUUM ADVANCE. You have 12 degrees initial, plus 10 degrees (?) centrifugal, for 22 degrees total. This doesn't make sense. 12 degrees initial, plus 10 degrees (camshaft) of centrifugal advance which would be 20 degrees (crankshaft,) of centrifugal advance or 32 degrees total
. Now we're making sense. Then you add vacuum advance, which moves the advance to 51 degrees. Either you have more than 20 degrees of centrifugal, or you have more than 10 degrees of vacuum advance. Is your "10 degrees" of vacuum advance camshaft degrees? That would be 20 crankshaft degrees, added to 32 total degrees of advance, for 52 degrees of total + vacuum. Very close to the 51 degrees you're claiming.
Are you SURE the centrifugal is all done advancing at 3000 rpm?
51/52 degrees of total + vacuum advance is probably a little high for Vortec heads. See how the engine responds
to knocking a couple of degrees from the centrifugal advance, and knocking about five degrees from the vacuum advance. ~30 degrees total, ~45 total + vacuum.
Ported vs. manifold vacuum--whichever the engine "likes" more.