A far better description.If you have recurve your distributor and modified the width of the advance slot then one of the best ways to take some of the guest work out of what you have as initial and mechanical advance is to set your timing at the highest "all in" rpm's. Using your timing light have someone slowly accelerated the rpms until you no longer see any advance in the timing and then set your timing as the desire number - usually at 36 degrees for most engine. Depending on the springs you used this should be somewhere between the lows 2 to low 3000 rpm range.
Once you have this number let the engine come back to idle and take a reading. Subtract the idle timing from the total and the difference is what you have as advance. You can then make adjustments as needed to either the initial or if needed the amount provided by the advance slot. Remember that your total combine should not exceed your engines recommend amount. This might call for additional adjustment to the advance slot to get the final numbers you want as far as initial and advance. You can also bend the spring tabs to change spring tension to adjust how quick the advance comes in.
Remember not to exceed the amount of total timing that is recommended for your engine.
Here are the degrees and slot widths.A far better description.
Edit: I should mention that I had to tig weld a wider slot on the outer side end, then file it to a dimension of .410". I don't remember where I found that number, but it is correct. This may be tricky for someone without access to a tig welder.
Do you have 15L? That is a very commonly used slot width. 30 degrees c/a + 6 initial = 36 total mechanical.Here are the degrees and slot widths.
8L slot = 16 degrees centrifugal advance = .358”
9L slot = 18 degrees centrifugal advance = .384”
10L slot = 20 degrees centrifugal advance = .410”
11L slot = 22 degrees centrifugal advance = .436”
12L slot = 24 degrees centrifugal advance = .462”
13L slot = 26 degrees centrifugal advance = .488”
14L slot = 28 degrees centrifugal advance = .514”
To find a slot width take the degree you are wanting and multiply it by .013 and then add .150 to account for the pin width. So a 15L (30 degrees) = 30 x .013 + .150 = .540 width.Do you have 15L? That is a very commonly used slot width. 30 degrees c/a + 6 initial = 36 total mechanical.
So glad we have a mathematician amongst us!! Thanks Kilgon. That could be a great help to others........... and myself.To find a slot width take the degree you are wanting and multiply it by .013 and then add .150 to account for the pin width. So a 15L (30 degrees) = 30 x .013 + .150 = .540 width.
That piece of plastic looks pretty beat up unless it's just the way the picture make it look like. I too bought a dizzy that had the plastic sleeve and why I previously mentioned it might be a quick fix, but to be honest, I have no idea if it was a Ford thing or not. The problem with the sleeve is it does reduce the travel width, but it also acts on the other side, reducing the "at rest" position by the thickness of the plastic, if that makes sense.Kind of a continuation of this thread. I bought this dizzy off of flea bay because of price and condition. It is supposed to be for a 1970 351C so I thought it would have the 10L/13L slots. It is a Ford reman dizzy, and the parts sure look good but it has the 13L/15L slots, and it is set to the 13L slot but the arm does have a plastic bushing inserted over it. Does this mean it was altered by Ford for the 20 degrees of advance instead of the 26 degrees? If anybody knows about this please let me know. Thanks!!
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