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  #1  
Old 06-07-2009, 11:29 AM
flatbill flatbill is offline
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Default distributor advance tuning

I'm new here and hope someone can help me. I am working with a '77 electronic distributor and want to modify it for more centrifugal advance. I am set to 12 degrees initial and the centrifugal tops out at 10 degrees more at 2000 rpm. I find that I can get lighter springs to make the advance come in quicker. Can I open up the advance slots to allow more centrifugal advance? I assume that this is the way its done. I have another distibutor that is a '74 electronic. I think this distributor may have more centrifugal advance built in but I have not been able to find specs on it. The distributor number is 3656763. Is there a source online to find distributor advance specs for a given year of distibutor? Thanks to all. Bill
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  #2  
Old 06-07-2009, 03:43 PM
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dave5711 dave5711 is offline
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Sorry, I don't know where you would find specs like that, BUT...
There must be something stuck or wrong with the 77. I've never heard of a factory distributor with that little advance. Usually mechanical advance in a stock unit is more like 24-28 degrees.

Lengthening the slots would be the way to do it, but normally this is never necessary. Usually a modified engine needs more initial, and thus LESS mechanical in the curve or a reasonable total timing(34 to 36) will be exceeded.

Most often the mechancal advance needs to be reduced, not increased.

What is the application?

What sort of combo are you running?(motor, compression, cam, gear, car, etc..)
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  #3  
Old 06-07-2009, 06:14 PM
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The factory advance curve in that time frame used one medium weight spring and one very stiff spring with an elongated loop. The initial advance was controlled by the medium weight spring until the loop was taken up in the stiff spring then the advance was very slow and was not all in until in some applications 4000+ rpm.

I would rev you engine well past 2000 rpm to see if it continues to advance. If it does swapping out the stiff spring for one of the light springs in the two spring MP kit works well. When combined with the medium spring you will have all the advance in around 2500-2700 rpm.

Of course if it does not then I would look for some sort of mechanical interference as dave5711 suggested.
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  #4  
Old 06-07-2009, 10:04 PM
flatbill flatbill is offline
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Default distributor advance tuning

I picked up the specs on the '77 distributor from a 1980 Motor's Manual. It spec out 10 degrees max centrifugal advance at 2000 rpm and 12.5 degrees vacuum advance at 12 inches of vacuum. I am running 12 degrees initial advance. The vacuum advance is hooked up to ported vacuum. I'm looking for about 30 degrees of initial and centrifugal, then I'll play with the vacuum advance for use on light load cruise. The 30 +/- 2 degrees was suggested by Bob Walker at Hot Heads.

This is a '56 Desoto 330 inch hemi with 9 to 1 compression, a mild Racer Brown EH-61 cam and a 600 cfm Holley carb. I have some home built tri-Y headers and dual 2 1/4 inch exhaust, a TKO 600 5-speed and 3.55 gears. Its in a 1950 Merc that weighs in at 3670 pounds. If I could find or borrow a Motor's Manual that included the '74 models, I could get the info. The Motor's Manual goes back to '75 and that distributor has about 15 ot 17 degrees of centrifugal advance.

I finally got my old Sun distributor machine running, so I'll be able to see what any modifications do. I see that elongating the slots will be needed. I think I can get the HP distributor springs from a local speed shop. I'll run up the '74 distributor and make modifications from there.

Thanks for all the help. Billk
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  #5  
Old 06-08-2009, 12:19 PM
passing you passing you is offline
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Hey Billk, set the total timing w/full advance to 30*-34* degrees
Then check the initial and report back.

Ain't nothing wrong with having 20*-26*initial it makes for more responsiveness, milage, but like said it makes it snappy & tire rippin.

This is a good thing for you since you don't have to modify anything in the distributor.

I've done the same w/ my 340.
I run 26*initial 34*@ full advance.
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  #6  
Old 06-08-2009, 12:59 PM
flatbill flatbill is offline
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Default distributor advance tuning

I will try both suggestions,

setting the total advance at a high enough rpm to get all the centrifugal advance in ,then seeing what the initial advance is.

running the rpm up to see what happens at a much higher engine speed.

Thanks, I will report my findings. Billk
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