Hi all,
When setting timing with a vacuum gauge, do you leave the vacuum advance connected? I know its disconnected when setting base timing with a light, but I'm using a vacuum gauge. All the vids I watched make no mention of disconnecting it so I"m assuming it remains connected.

Thanks
Steve

 

You can't set timing with a vacuum gauge. It won't even get you close to correct timing. Complete nonsense propagated by hacks on the internet. Get a real timing light.

 

Damn internet. When you give direction and Jebbysan agrees, that is the direction I follow. Timing light it is!

Thanks guys

 

E-mail me if you need a copy of my paper on how to set the timing up correctly. It does not involve a vacuum gauge...

...and by the way: If you set the timing up to produce best vacuum at idle using a vacuum gauge, your total timing will be so over-advanced that you will end up with detonation at wide open throttle and stand a damned good chance of breaking the piston groove lands off your pistons and hammering your rod bearings to the point of spinning a rod bearing. Very bad idea, wherever you got that from. Don't ever do that.

Lars
V8FastCars@msn.com

 

Hi Lars,
I have the timing papers you sent to me last spring. Its version AK 1-2-22. Is this still the most current?
Steve

 

If you have the correct procedure to set the timing, why in the world are you screwing around with a vacuum gauge..?

Current revision is "AL" dated June '23.

 

LOL. Good question. I have a dial back timing light and I ain't afraid to use it, and I have used it many times. But I came across the vacuum method that 'the internet' appeared to be quick and easy and I was lured in. Fortunately, I didn't get around to mess around with the vacuum gauge and heeding your advice, I wont. Like everything else, what appears to be the quick way is never the right way.......I'll be emailing for the current papers.

Steve

 

The force of the dark side is strong......LOL....

Jebby

 

Lars and Jebby,

Been following this thread with interest.

Please debunk or confirm what I was told by an old-timer mechanic years ago: You can determine overall engine health with a vacuum gauge. Theory explained is if the rings are worn, valves have poor seats, and seals are bad, the engine will not produce much vacuum.

I am not making this claim. This was told to me.

Bunk???

 

I'm going to slightly and respectfully disagree with a couple of the posters here (and probably the internet video as well), as I don't see that you're getting the whole story, which can lead to confusion and/or engine inefficiency/damage.

I see nothing wrong with using a vacuum gauge to see/determine what idle timing your specific engine wants at your specific climate/altitude. All engines are slightly different, and the factory timing is usually conservative as it has to be a one-size-fits-all for the production run. Adjusting your timing while monitoring improvements in manifold vacuum (indicating changes in combustion thermal efficiency) gives you an indication of what YOUR engine wants at that particular moment/weather-condition. This work will help with setting an idle timing that gives you the best idle quality and cooling efficiency while sitting at the stoplights.

But this is just half the job. As noted before, you could risk engine damage at high RPM WOT runs, as your upper RPM timing may be too highly advanced if you bump up the idle timing significantly.

The other half, as mentioned earlier, is to set your high RPM timing to a designated number that has been shown to be safe in a reasonably wide range of engines. The downside here is that the idle quality and cooling ability concerns are not addressed, as the idle timing is just left to whatever it ends up being. Your engine spends more time idling and at low RPM cruising than at WOT, so it seems that low RPM timing should be given some thought too.

The problem is, you can't have both with the stock curve distributor. You either have the top end timing you want, or the low end timing you want. If you want the best/optimum of both "worlds", you would have to look into having your distributor recurved by a service that does this for others.

In the end, it's your call on how much time and effort/money you want to put into your engine tune. FWIW, I thought the time and effort was worth it for my engine.

 

For a mild SBC build, what’s the maximum recommended total idle timing (initial plus vacuum advance).

 

If the vacuum is noticeably low on the gauge to the point it is concerning....you will see pretty good oil consumption at that point.....if the rings are wore out to compress, they are wore out to draw too.....generally the bore wears much more than the rings and have a lot taper at this point too.....
Vacuum gauge is better used to find leaky valves.....bad idle tune....things like that....

Jebby

 

27 with vacuum can plugged to full manifold vacuum at idle....15 actual, 12 vacuum....with most original HEI's that puts you at 36 degrees total.....

Jebby

 

Although I consider Jebby's answer to be a fairly good answer.
Me, I'd ask, define mild build.
what compression ratio? Which heads? What cam?
None the less, a fair answer for 9-1 compression and iron heads.

 

Mild build to me means 350hp....15+ inches of vacuum.....

Jebby