Vacuum Advance and why to use it on the street

[Keith Tedford]

The original factory advance setup in 1969 wasn't even for performance. It was to pass emissions tests. Our 427 came with #68 primary jets and had lean surge at sixty mph. The advance curve was long and slow, not coming in full until about 5K rpm. I forget the exact number any more but I bumped up the initial timing and played with various springs and weights. The difference in performance was impressive. That was when we could get 104 octane gas. With the 91 octane today you can't run nearly as much total advance. I had our L78 running reasonably well but it sure wasn't running original factory specs in the distributor. It will run but not all that well.