Fuel can ony burn so fast inside a cylinder. At higher RPM the ignition needs a headstart in order to get peak cylinder pressure around 10° after TDC durning powerstroke. Under heavy load advance is very dangerous, and can lead to pinging and spark knock.
Most distributors are equipped with vaccuum and mechanical advance. Mechanical involves centrifigual weights that turn the distributor cap to advance timing. Vaccuum advance is mounted on the side of the distributor and sources vaccuum from the intake or carb.
When setting your timing with a light you should do it with the vaccuum advance unhooked at around 2000 rpm. Or at least thats how I do it.
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93 Thunderbird 5.0 HO
89 Firebird L03
95 F150 XL
Get ready for the 351 boss build this summer, 4v closed chamber heads, 2.25/1.75 valves, .750 lift, 12.5:1 piistons, wieand tunnel ram, nitrous, I think its gonna roar!
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