Setting timing on the 454 using vacuum gauge

[gmehal]

Has anybody done this? if so what was your reading? Mine started at 15 and I raised it to 20. It went a little higher but I backed off a bit. Seems to run great but curious about others numbers.

[tpi]

I strongly don't recommend setting timing using vacuum.

This is likely to lead to excessive advance. When the engine is idling typically the vacuum advance is offline for emissions reasons. The engine would typically like much more advance at idle than the factory sets up. However off idle, the vacuum advance kicks in and the centrifugal advance adds more with additional engine speed. With this additional advance, any timing set by vacuum would quickly lead to too much spark advance.

Use a timing light and set to factory spec. Confirm centrifugal and vacuum advance are working properly. You may be able to go a couple degrees on either side of the spec for specific conditions, but always listen for pinging/detonation which indicates too much spark advance.

[jonesy 1]

vacuum works as a way to set timing on an older motor 20 in. is a little high , this is from memory 15-18 in. is the green aera of the gauge Iuse a light and a gauge because you need the gauge to set carb after timing ,the light will check advance cent.and vac. and 2degrees advance is better with the gas today.hope its helpful,

[dadstoy]

Well what ever anyone thinks, you can't properly set the timing via vacuum nor by feel. Proper instrumentation is your best friend. Besides, why would you not want to use a timing light...basic timing lights are cheap!

I set my '81 454 at 4 degrees advance for smog testing. I haven't changed it and there was no audible pinging on my last 1000 mile trip mostly over mountain between California and Oregon with many 6% grades lasting 8 to 10 miles each.

I would like to do some experimenting with the advance curve and jetting on the Quadra-crap, but I certainly wouldn't do this with out using a timing light. Now, my other issue is that I can't find any information nor anyone that knows how for a non-race car 454...sad!