Also, FWIW, I have never limited the vacuum advance can. I don't worry "how much" it pulls in. The MP engine book says 60* total is not uncommon. It's not how much, but when it pulls it in. Only at very light part throttle. That's to help clean up the combustion process so as not to have it "backing up" in the combustion chamber at very light throttle......if that makes sense. Since vacuum drops out on acceleration, you'll never see that much on accel anyway, so no danger of detonation.