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Old 11-20-2003, 11:42 PM
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how much mechanical advance does a stock distributor have?

can someone tell me how much mechanical advance the average h.e.i distributor produces?? also, how much does the average stock vaccum advance pull? thanks

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Old 11-21-2003, 01:20 AM
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Plug your vacuum advance. Use an advance analyzing timing light and a tach. See how much the timing advances and what RPM it stops advancing at. Distributor parts can wear or might not have ever been right. It is better to check yours and find out for sure.
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Old 11-21-2003, 07:25 AM
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The advance curve of any stock distributor was tailored at the factory to suit the needs of the engine and chassis that it was originally installed in.There's to many combos of vacuum and mechanical advance to accurately say what you have.And as the distributor wears out the advance numbers will undoutedly change.
Check your vacuum advance by first disconnecting the vacuum hose and pluging it to avoid a vacuum leak.hook up your timing light and measure the initial advance,then reconnect the vacuum line to the distributor and measure the * of change at idle.The * of vacuum advance can be changed by changing the vacuum canister on the distributor.GM has made many different ones over the years so it is possable to find the one with the * of advance you need for your car.
the mechanical advance is a little harder to measure but a timing light,tach that you can read from under the hood,and a screwdriver are all that's needed.
first disconnect your vacuum advance hose and plug it.
then with the tach and timing light hooked up,start the engine and measure the base timing at IDLE.write this number down.
then with the screwdriver slowly turn the idle speed screw up on the carb and watch the timing change as the RPM goes up.
At the RPM point when the timing stops advancing,record the RPM reading and number of * of advance at it's most advanced setting.
Subtract the initial advance reading from your total advance number and this is your mechanical advance * at the given RPM it reached it.
Wasn't that easy!!!!!!!!
just one other thing,check your mechanical advance weights and springs to make sure they aren't sticking or broken as this is a common problem on HEI distributors.
to change the advance specs requires changing parts and remeasuring the * advance to make sure it will be what you need it to be.Don't just install parts and assume it will be correct.
I hope this explaines the procedure in enough detail to help.
I've found over the years that ignitions are the most missunderstood part of engine building.
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