timing engine using vacuum gauge?

[bstan70rr]

i was listening in on a conversation about timing engines using a vacuum gauge. i was distracted before i could ask any questions.

can anyone explain this process?

 

[george68hemirr]

no...i wouldnt do it with a vacumn gauge....what happens if you have a vacumn leak...then what??

 

[moparchris]

Whoever was having that discussion probably was going to talk about replacing melted pistons next. I would never do that, you could very easily run into detonation when the distributor advances. I would rather time it by ear before resorting to a vacuum gauge. At least you can hear it blow up when you do it that way.

 

[mcmopar]

I don't time it with a vacuum guage. A vacuum guage is helpful in tuning, however.

 

[A31PKG]

There are lots of opinions on this subject....Here's my 2 cents: If your engine is stock, and everything is functioning as designed, then the factory spec should be fine. However, especially if you have a modified combo, the factory spec will probably not always provide the best performance. In this case, using a vacuum gauge can help you find the "sweet spot"...or at least a starting point from which you can fine tune the setting. Basically, it works like this: With a warmed up engine, install a vacuum gauge to manifold source (a source below the throttle plate) and allow the engine to idle. Disconnect the vaccum advance hose from the distributor and plug it. Observe the vaccum reading, and carefully rotate the distributor back & forth until you get the highest steady reading. Then back off (retard) the timing about 2 inches and lock it down. Reconnect the hose to the distributor. You may have to adjust the idle a few times while doing this...This will get you in the ball park. From there a little trial and error - in 2-degree increments - should get you the best performance out of a given combo. Of course, there are much better (and more accurate) ways of establishing optimum ignition advance curves, but in the absence of a dyno or distributor machine, this should work. Always remember that detonation is BAD...and that you cannot always hear it...If your compression ratio is higher than, say, 8.5 to 1, then this procedure should only be followed in conjunction with a higher octane fuel...Cam II and such....Also the weight of the car, gearing, how it's used, etc, all factor into the equation. Again, if the car is basically stock, at or near spec is the way to go. Hope this helps!

 

[george68hemirr]

There are lots of opinions on this subject....Here's my 2 cents: If your engine is stock, and everything is functioning as designed, then the factory spec should be fine. However, especially if you have a modified combo, the factory spec will probably not always provide the best performance. In this case, using a vacuum gauge can help you find the "sweet spot"...or at least a starting point from which you can fine tune the setting. Basically, it works like this: With a warmed up engine, install a vacuum gauge to manifold source (a source below the throttle plate) and allow the engine to idle. Disconnect the vaccum advance hose from the distributor and plug it. Observe the vaccum reading, and carefully rotate the distributor back & forth until you get the highest steady reading. Then back off (retard) the timing about 2 inches and lock it down. Reconnect the hose to the distributor. You may have to adjust the idle a few times while doing this...This will get you in the ball park. From there a little trial and error - in 2-degree increments - should get you the best performance out of a given combo. Of course, there are much better (and more accurate) ways of establishing optimum ignition advance curves, but in the absence of a dyno or distributor machine, this should work. Always remember that detonation is BAD...and that you cannot always hear it...If your compression ratio is higher than, say, 8.5 to 1, then this procedure should only be followed in conjunction with a higher octane fuel...Cam II and such....Also the weight of the car, gearing, how it's used, etc, all factor into the equation. Again, if the car is basically stock, at or near spec is the way to go. Hope this helps!

very well said

 

[6R9Runner]

It sounds like a way of setting initial advance only. A vacuum gauge can also be used to set idle mixture.

 

[A31PKG]

X2