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1966 El Camino
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The vacuum advance is usually used during street performance to advance the timing when stopped at a stop light or stop sign. This advance helps the engine smoother during those periods when stopped and actually help with fuel economy.
Can someone explain why this is a bad thing on a street car?

Mechanical advance only makes perfect sense on a car that spends most of its time at WOT , rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation.

A street operated vehicle without vacuum advance is sacrificing idle cooling, throttle response, engine efficiency at part throttle/cruise, and fuel economy.
 

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1966 El Camino
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2,301 Posts
Its not a bad thing. There is nothing wrong with vacuum advanced distributors. Everything has it's purpose.

A properly set up mechanical advanced distributor is going to out perform a vacuum advanced distributor. Mechanical advanced distributors allow you to install different bushings and springs so you can fine tune the timing on your specific engine, which means, easier starting, smoother idle, better acceleration and WOT.
This is possible on every distributor I've ever owned, all of which were equipped with vaccuum advance. Since at WOT there is no vaccuum advance, there should be no difference between a properly setup mechanical only distributor, and an equally properly setup mechanical + vacc distributor, except that in situations other than WOT the vaccum equipped one will be better.
 
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