Vacuum test and Dwell...46´59AB

Harylufa

Harylufa

Senior Member
Vacuum test and Dwell...46´59AB

Hi!
Today I tested the vacuum and dwell with a timing light that I bought.

I attached a video about the test. I see that my engine is (setting the timing light) 8 cylinder and it is at 34º with 600 RPM. Is this correct?

http://www.youtube.com/watch?v=nON4Gjn1HZ4

I read that 36º at 600 RPM is the correct.

Vacuum gauge is marked at 18/20 in green range.

If there is something wrong please let me know.

Thank for reading.

Hary
 
Re: Vacuum test and Dwell...46´59AB

36 is the spec but 34 isnt that far off. For every degree of dwell timing changes 2 degrees . So timing would be off 4 degree at the crank...
 
Re: Vacuum test and Dwell...46´59AB

BUBBAS IGNITION said:
36 is the spec but 34 isnt that far off. For every degree of dwell timing changes 2 degrees . So timing would be off 4 degree at the crank...
Click to expand...

Bubba!
ok, must I retard or advance in the distributor to complete the 36º?

Thank for helping us.

Hary
 
Re: Vacuum test and Dwell...46´59AB

Changing timing doesn't change dwell. Changing dwell changes timing. Dwell is changed by adjusting the gap of the points in the distributor. Not an easy task on these distributors. I would say you are as close as you're going to get without a distributor machine to put the distributor on after removing it to get the dwell any closer. You are way close enough. Two more degrees would not make any noticeable difference in operation or performance of your engine in my opinion and experience.
 
Re: Vacuum test and Dwell...46´59AB

One more thing. As a practical matter I believe timing is best set with a vacuum gauge to maximize vacuum at idle rather than trying to get it right on geometrically. And, best initial timing can be very different at varied altitudes. At 5,000 feet where I live I have to advance my timing all the way to maximize vacuum and get maximum power and performance out of my engine.
 
Re: Vacuum test and Dwell...46´59AB

If my reasoning is correct, a slightly wide point gap will produce the lesser dwell reading. If so, the normal wearing of the points' rubbing block could gradually bring the dwell into spec. I would leave them alone.
 
Re: Vacuum test and Dwell...46´59AB

Old Henry said:
One more thing. As a practical matter I believe timing is best set with a vacuum gauge to maximize vacuum at idle rather than trying to get it right on geometrically. And, best initial timing can be very different at varied altitudes. At 5,000 feet where I live I have to advance my timing all the way to maximize vacuum and get maximum power and performance out of my engine.
Click to expand...

Depending on the distributor curve, the best idle timing might or might not be the optimum cruise timing. I wonder if any testing has been done to establish cruise RPM timing with the vacuum gauge?
 
Re: Vacuum test and Dwell...46´59AB

The point gap, which corresponds to the dwell angle, can be from 0.014 to 0.016 inches. That's a 12% leeway. Applying that to your dwell angle of 34° gives a leeway in dwell angle of 4°. So, you're well within that range.
 
Re: Vacuum test and Dwell...46´59AB

Old Henry said:
Changing timing doesn't change dwell. Changing dwell changes timing. Dwell is changed by adjusting the gap of the points in the distributor. Not an easy task on these distributors. I would say you are as close as you're going to get without a distributor machine to put the distributor on after removing it to get the dwell any closer. You are way close enough. Two more degrees would not make any noticeable difference in operation or performance of your engine in my opinion and experience.
Click to expand...

Old Henry!
If you saw the video, you can see dwell is 34º and as you say it is very close to 36º.

I understand this:

"Changing timing doesn't change dwell. Changing dwell changes timing. Dwell is changed by adjusting the gap of the points in the distributor"


Now, if I advance/retard the dist, what for? which the effect in engine?


My engine is running good now after 17 year. And its interesting to hear engine sound being now in timing.
Thank for helping me
Harry
 
Last edited:
Re: Vacuum test and Dwell...46´59AB

Old Henry said:
One more thing. As a practical matter I believe timing is best set with a vacuum gauge to maximize vacuum at idle rather than trying to get it right on geometrically. And, best initial timing can be very different at varied altitudes. At 5,000 feet where I live I have to advance my timing all the way to maximize vacuum and get maximum power and performance out of my engine.
Click to expand...

Old Henry!

Where I live we are at sea level, perhaps I do not need advance the distributor. Am I right?

thanks
 
Re: Vacuum test and Dwell...46´59AB

Harylufa said:
Old Henry!

Now, if I advance/retard the dist, what for? which the effect in engine?

Thank for helping me
Harry
Click to expand...

Change of timing changes efficiency and power of engine but only in a small amount not very noticeable.

Harylufa said:
Old Henry!

Where I live we are at sea level, perhaps I do not need advance the distributor. Am I right?

thanks
Click to expand...

You are probably right about that. You could try it and see what happens to your vacuum gauge just to see if it improves any.
 
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