The first task was to determine the amount of vacuum the booster was getting. Power brake boosters require at least 18 in-hg (inches of Mercury) from the inlet manifold at idle to operate correctly. With the vacuum hose disconnected, the gauge was fitted in its place, and the best reading achieved was 17 inches, though the gauge shows 15 1/2 here. A performance cam will affect the vacuum, but this is a stock rebuilt motor with an Edelbrock Performer inlet and carb, so the vacuum should be unaffected. I elected to conduct all the tests for the purpose of this article with the vacuum at 17 inches. Though Classic Performance Products offer an electric vacuum pump to remedy this, I'm going to investigate further as there has to be a reason the vacuum is so low.