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Old 07-08-2012, 08:59 AM
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cobalt327 cobalt327 is offline
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Originally Posted by 64Joker View Post
I'm interested in just "checking" my timing mark on my 64 Chevy smallblock, do I still need to plug the distributor vacuum hose? I don't plan on adjusting at this time!
Disconnect and plug it to check the initial advance (initial advance is the timing at idle). But the initial advance is not all of it- you really need to know what the total timing is (total timing = initial plus mechanical)- or else the engine can be damaged or have poor performance from detonation or insufficient advance at higher RPM.

To check the mechanical advance, use a timing tape or a dial back timing light and accelerate the engine until the mechanical advance quits advancing. The reading there is the total timing. The total timing for most SBC engines should be around 36 degrees, less for Vortec or 'fast burn'-type heads.

If you want to know how much the vacuum advance adds, attach the vacuum line to the vacuum advance and at idle take a reading. Disconnect it and take another reading. The difference between the two is the vacuum advance. Usually you need about 10-12 degrees from the vacuum advance. Stock vacuum advance cans often add more than that.

The combined advance (mechanical plus initial plus vacuum) should fall somewhere around 50 degrees under light throttle cruise conditions (engine vacuum high, throttle setting relatively low).

More on timing here, including how to make a timing tape and how to tell if the timing marks are accurate.

Last edited by cobalt327; 07-08-2012 at 09:05 AM.
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