timing with vacuum gauge

40cpe

40cpe

Well-known member
I understand about setting timing at idle with a vacuum gauge. Is there a benefit to setting the total advance at cruise RPM by vacuum readings? If so, is it done by setting the distributor for max vacuum, or do you back off or add timing to max vacuum? I've never heard this discussed.

This is on a 5.0 engine that has been converted to a carb and points distributor with a Pertronix unit. I doubt the curve on this dist. is set up for an ideal curve for this engine.

Thanks for any insight.
 
If you have a timing light, and the balancer is marked well, you can figure out your curve. If the distributor is unknown, it may be better to send it to GMC Bubba. He goes through to make sure everything is right, and puts in a custom curve for very little money. It will be back in two weeks and be trouble free. He can be found over on the HAMB.
 
Yeh, me too. I have exact same set up. Could someone take the time to tell us how to set the timing with a vacuum gauge? Would appreciate. Thank You.
 
Connect the vacuum gauge to manifold vacuum. Disconnect and plug the vacuum to the distributor, loosen the clamp bolt on the distributor and then with the engine at idle, preferably at about 500-600 rpm, rotate the istributor to where you get the smoothest idle and highest steady reading on the vacuum gauge. Then rotate it backwards to drop the reading by 1" of vacuum. Tighten the bolt but not fully. Connect the distributor back up and remove the vacuum gauge.
Take the car for a drive and listen to the engine, you should have a very light ping under heavy load in top gear. You may need to move the distributor back a little more if the ping is too heavy.
Once that is done tighten the distributor fully. An engine should idle with a steady reading of between 15-18" of vacuum.
This has always worked for me. The harmonic balancer ring on y-blocks is notorious for moving rendering the timing marks useless.
 
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