[Stuckinda60s]

Once again, you want manifold vacuum, not ported. Set the timing at 12* at idle-with the vacuum hose plugged, then make sure you get the full 20* out of the distributor. Then, hook up the manifold vacuum and reset the idle speed and readjust the carb.

I know some use ported, but there're some very good reasons why Pontiac always used manifold. If you can drill out the idle passages and go through the carb to optimize it for the best idle by adding fuel, you can set the engine up for ported, but for most of us, that's not an option.

For those who don't think it works, a friend of mine was recently chasing some problems with a fresh 455 with the 274 XE cam and cleared them all up by going to manifold vacuum. It really woke the engine up. I've used manifold in every engine I've ever built and run on the street. I've tried ported and always gone back.

Low compression engines love timing. I've run more initial at times than I thought prudent, with manifold advance on top of it and still had no complaints out of the engine. I ran a 400 Pontiac in my GMC pickup with a Performer cam and manifold, Rhoads lifters, manifold vacuum, and a worked distributor and it still liked 16* initial. The truck had tremendous torque, and out-towed a lot bigger engines with ease, even though I ran a stick and higher gears and my friends ran 454-auto's and low gears.

My suggestion? Try it both ways. You can tell which is which on the carb by determining whether the vacuum tap is above or below the throttle blades. Ported will be above the blades. Just make certain you reset the idle and carb, whenever you change over.