318 cam shaft selection/upgrade for stock engine

MObarracuda said

I work for Cardone (nations largest family owned auto part reman company) and had my booster rebuilt by my company. The Manager of the custom rebuild department told me the small diameter boosters need 18-20 of vacuum to work properly. My old 273 could barely muster 15-16 and the assist was marginal.

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OK, that is good info and makes all the sense in the world.

One thing you might want to consider is a vacuum reservoir; it is just a family size pork 'n beans can thing with a check valve that 'stores' vacuum (i.e., stores 'nothing' LOL) and so you will always a have some high level of vacuum ready to go. It will store vacuum at the level that you had when last decelerating with the throttle closed, which, with a decently tuned carb, is easily in the low to mid 20's with a 268-ish cam. I've used one on a turbo rally car and they work fine; they just run out of 'nothing' if you pump the brakes real fast a few times.

Of course, the vacuum reservoir won't fix low compression pistons....