re: ZZ4 upgrades?
This is the part that everyone questions
"Set spark timing at 32º before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle (WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve"
That doesn't mean to leave the vacuum advance disconnected permanently.
It means to verify what your total advance is (centrifugal + initial) , you don't want vacuum entering the equation because it doesn't operate at wide-open throttle.
Always connect the vacuum advance to full manifold vacuum - if you want the engine to run cool and get good mileage - and be easy to start.
67 Chevelle convertible, 138 vin, original 4 speed, bucket seats, Marina Blue with black interior