Related Photo Galleries
The first task was to determine the amount of vacuum the booster was getting. To operate correctly, power brake boosters require at least 18 inHg (inches of mercury) from the intake manifold at idle. With the vacuum hose disconnected, the gauge was fitted in its place, and the best reading achieved was 16 inches, though the gauge shows 151/2 here. A performance cam will affect the vacuum, but this is a stock rebuilt motor with an Edelbrock Performer intake 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 16 inches. Though Classic Performance Products offers 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.