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Vacuum Advance VarietyA sufficient amount of vacuum advance can significantly improve throttle response in light load conditions, but too much can lead to audible detonation. While part-throttle detonation won't likely cause catastrophic engine failure (as long as it subsides as engine load increases), the sound will surely make any driver uneasy. An adjustable timing light can be used to determine just how much vacuum advance your Pontiac can tolerate.After setting base timing and properly adjusting the distributor's centrifugal advance curve, disconnect the vacuum advance unit and adjust the timing light until the variable and stationary TDC marks are aligned, and record the amount on the dial or digital display (this should be the same amount as base timing). Connect the vacuum advance canister to a manifold vacuum source or a handheld vacuum pump. Readjust the timing light so the variable and stationary marks are again aligned, and record that number. The difference between the two is amount of vacuum advance available. Installing another stock-type vacuum advance unit providing a lesser amount or an adjustable aftermarket piece should clear up any detonation with no ill performance effects.