Thread: Need help
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Old 04-06-2015, 02:42 PM
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drvnmsbessie drvnmsbessie is offline
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Join Date: Jun 2009
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Most hei vac cans provide 20-23 degrees of advance with a static of say 10 plus mech adv of say 12 your at 42-45 total whereas 28-32 is max. Hei vac with stock profile cams runs best with manifold vac. Some Small rv type cams like ported a little better. The real gains with vac. Advance is in mileage so you can run without it. So, set timing at stock spec. With adv.Disconnected ,snug dist. Rev motor to 2200 rpm or so and check timing at this rpm. This number minus your static number is your mechanical advance. Now with the engine running apply vac. To the vac. Adv. and check it again at idle. This number minus your static number is the amount of vac. Adv. you have. So add static,mech and vac. And what do you have.
As a side note a dial back timing light is best in this situation.
Adjustable vac advance pots are available at most parts stores as well as hei mech. Adv. weights to tailor your mech adv. as well.

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