Questions about using a timing light

[68 P.O.S.]

You only use ported if your engine is running an EGR valve for emissions. Straight from the GM developmental horse’s mouth: ““Ported Vacuum” was strictly an early pre-converter crude emissions strategy and nothing more. Don’t believe anyone who tells you that ported vacuum is a good thing for performance and drivability – it’s not. Anyone with a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy…”. Call me weird or call me crazy, but I'll believe the GM engineer who helped develop the system.