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Old 02-26-2004, 02:58 PM
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What is total timing?

I have a crate motor from GM ZZ4 it recommends 12 degrees BTDC @800 RPM's ,36 degrees total w/vaccum advance disconnected. I have a timing light and i know how to check the first part (12 degrees @800 RPM's) but how do i check total timing?

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Old 02-26-2004, 05:06 PM

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Since no one has jumped in on this, here goes. Total timing is the timing when the mechanical/vacuum advance is added in. You will need a mark at the 36 degree point . Then you hook up your vacuum advance and run the motor to the recommended RPM that total timing is to occur (Should come with your engine specs) Using the timing light in the same manner, the mark should appear at the standard pointer. If you don't have it, then you will need to change out your mechanical weight springs or adjust your vacuum advance, if you have an adjustable one. (this used to be done with a small screwdriver in the vacuum tube; don't know about the later model stuff)


PS, 36 degrees total may be a bit high unless this is an all out race application. 34 degrees is more the norm.
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Old 02-26-2004, 05:19 PM
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Re: What is total timing?

Originally posted by shockers69
36 degrees total w/vaccum advance disconnected.
They're referring to total mechanical advance. You want to have 36* all in by 3000 rpm w/o the vac. can hooked up. When you floor it the vacuum adv. shouldn't be adding because of the low manifold vacuum. You should try to have a can that only brings in another 10-14 deg. additional timing, or leave it disconnected.
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Old 02-26-2004, 05:26 PM
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The 36* total timing they are referring to is with the vacuum advance disconnected. This is your base timing plus whatever mechanical advance your distributor applies. Once your base timing is set start increasing RPM's while watching your timing marks (vacuum advance disconnected). At some RPM the advance will stop increasing. This tells you what your total mechanical advance is as well as what RPM you achieve it. Let's say your distributor provides 20* of mechanical advance at 3,500rpm's. If your base is 12*BTDC then at 3,500rpm's your timing light should show 12+20 or 32* of advance. This is the total advance at wide open throttle your engine would see due to the drop in manifold vacuum at wide open throttle. Under light load while cruising the vacuum advance provides additional advance on top of the mechanical.


Last edited by dmorris1200; 02-26-2004 at 07:20 PM.
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Old 02-26-2004, 10:42 PM
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The ZZ4 balancer has marks all the way to 60* BTDC on it. Put a dot of white paint or white-out at 36* if it's hard to see. Don't forget to hook the vacuum advance back up when you're done.
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Old 02-26-2004, 10:53 PM
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finanally i know now what total timing is, some people can expain it in a way that it is impossible to understand but dmorris1200 explained it perfectly.
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