I have a 65 FI car and a new total advance timing light. I just measured my total advance at 2800 RPM with the vacumn advance hooked up and it showed 54 degrees total advance. I looked in the 65 shop manual and it says centrifugal 26 degrees at 2500RPM, Vacuum 16.5 degrees at 8.2 Inchs HG, and initial advance of 12 degrees. Do I add those all together? So should it be 12+26+16.5=54.5 degrees? We run the race car at about 36-38 degrees so this seems like a lot! It seems like vacuum should not be added but I'm not sure. Can one of you engine experts help me out? Jerry
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Re: Total Engine advance C2
Sounds like you have it just about perfect. That's what the vacuum advance does: add advance at moderate throttle and "retard" advance at WOT -
Re: Total Engine advance C2
Sounds like you have it just about perfect. That's what the vacuum advance does: add advance at moderate throttle and "retard" advance at WOTComment
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Re: Total Engine advance C2
There are three "total" timing values.
1. Total idle timing
2. Total WOT timing
3. Total cruise timing.
Now, all you rocket scientists and engine gurus, how is each one measured and what should be the range for each?
DukeComment
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Re: Total Engine advance C2
There are three "total" timing values.
1. Total idle timing
2. Total WOT timing
3. Total cruise timing.
Now, all you rocket scientists and engine gurus, how is each one measured and what should be the range for each?
DukeComment
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Re: Total Engine advance C2
I'll take a crack at it.
Total idle timing is initial plus vacuum or 12+16.5=28.5
Total WOT equals initial plus centrifugal or 12+26= 38
Total cruise timing equals initial plus vacuum plus centrifugal or 12+16.5+26=54.5
Do I be a rocket scientist??? JerryComment
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Re: Total Engine advance C2
I'll take a crack at it.
Total idle timing is initial plus vacuum or 12+16.5=28.5
Total WOT equals initial plus centrifugal or 12+26= 38
Total cruise timing equals initial plus vacuum plus centrifugal or 12+16.5+26=54.5
Do I be a rocket scientist??? JerryComment
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Re: Total Engine advance C2
Depending on idle speed and springs, you might see a little centrfugal advance at idle as well. If everything is to spec, you probably shouldn't, but you can wrap a rubber band around the weights when checking idle advance just to be sure there is no extra advance sneaking in.Comment
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Re: Total Engine advance C2
Depending on idle speed and springs, you might see a little centrfugal advance at idle as well. If everything is to spec, you probably shouldn't, but you can wrap a rubber band around the weights when checking idle advance just to be sure there is no extra advance sneaking in.Comment
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Gold stars for Jerry and Ed!!!
True rocket scientists and engine gurus.
Total cruise timing is the sum of initial, full centrifugal, and full vacuum. Some engine's "cruise timing at up to 3500-4000 may not include full centrifugal if the curve does not top out until over 4000, but for the 64-65 mechanical lifter engines, full centrifugal of 24 degrees was all in at 2350, so they should show in the range of 54 degrees total at cruise speed of 2500 revs or more. These engines can use (and need) lots of spark advance, especially at idle and cruise due to the high effective valve overlap that creates a lot of exhaust gas dilution, which slows flame propagation speed. Full centrifugal can be brought in early because of the late closing inlet valve, which reduces the dynamic compression ratio to well below the static 11:1 ratio.
Ed also pointed out the very useful fact that setting initial timing on these engines is tough because the centrifugal starts at about 700. The best way to set the timing is to set "total WOT timing" by disonnecting the vacuum advance, revving to 2500, verifying that the mark does not advance with futher revs and then dial in 38 degrees on the dial back timing light, move the balancer notch to zero on the tap and lock down the distributor.
Then rev the engine to 6000 and verify that the balancer notch does not advance. If it does, the advance limit bushing may be deteriorated and allow too much advance at high revs.
DukeComment
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Gold stars for Jerry and Ed!!!
True rocket scientists and engine gurus.
Total cruise timing is the sum of initial, full centrifugal, and full vacuum. Some engine's "cruise timing at up to 3500-4000 may not include full centrifugal if the curve does not top out until over 4000, but for the 64-65 mechanical lifter engines, full centrifugal of 24 degrees was all in at 2350, so they should show in the range of 54 degrees total at cruise speed of 2500 revs or more. These engines can use (and need) lots of spark advance, especially at idle and cruise due to the high effective valve overlap that creates a lot of exhaust gas dilution, which slows flame propagation speed. Full centrifugal can be brought in early because of the late closing inlet valve, which reduces the dynamic compression ratio to well below the static 11:1 ratio.
Ed also pointed out the very useful fact that setting initial timing on these engines is tough because the centrifugal starts at about 700. The best way to set the timing is to set "total WOT timing" by disonnecting the vacuum advance, revving to 2500, verifying that the mark does not advance with futher revs and then dial in 38 degrees on the dial back timing light, move the balancer notch to zero on the tap and lock down the distributor.
Then rev the engine to 6000 and verify that the balancer notch does not advance. If it does, the advance limit bushing may be deteriorated and allow too much advance at high revs.
DukeComment
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