I have read and re-read a section on the www.fordmuscle.com site about the how to's of recurving the distributior. I am stumped as to how to know what the mechanical advance should be. I understand the static advance and how to quantify where the total should be, total advance at 2500 rpm?, but not sure about the mechanical. Any suggestions?







1971 F-350 1 ton dump, ground up fully restored w/ 360 motor

 

Ok, short run down on the advance. The cent. advance is contolled by two things, first is the weights inside, underneath the pickup plate. These are used to "pull" the plate as the rpm's increase, the weight wants to go out, away from center, the faster it turns the more it wants to "pull" outward. Second is the springs, these control at what speed and how fast the weight will be allowed to put it's "pull" on the plate. The heavier the spring is, the higher the rpm before getting full advance due to the springs holding back the weights. By the same token, the lighter the spring the lower the rpm until full centrifical advance is obtained. For what you want to do all that should be needed is the springs changed to lighter ones, this will allow full advance earlier. I think most are factory set to be in by around 3000 rpm's, however, on a stock engine, this won't do much for you. It will help some if you can get it dialed in. If you have some mods, such as timed the cam straight up in a 351M/400, headers, intake and carb, ect., ect. there is much to be gained by this. This part only contols how fast the advance will come in, how far you allow the weights to pull the plate will determine how much total advance it can have if it wants. Got a breathed on 460, I run 38 degrees total, all in by 2400 r's with 10 degrees of vacuum and 28 of cent. advance. Usually when I spoke with anyone concerning this, the intial timing was basically left out of the mix when talking advance/curve. If you have an adjustable vac. advance, you can overcome slight over-curve by using less on the vac. side of timing. Should not ping(anytime really!) uphill under load at highway speeds, part throttle, if it does, use the vacuum advance to get rid of it, if you can't, then you will have to change the springs. They aren't hard, just a pain due to pulling the pick-up and plate to get to them. Hope this helps!

 

I would like to relate what an race engine builder told me about timing and and distributors. Chuck P. is right on with everything he said except about the initial or static timing being left out of the total calculation. When I was messing with my dist, I thought you added all three- initial+vacuum+centrifugal. The engine builder corrected me and said your total timing is initial+centrifugal. He said the vacuum advance has no effect except at cruising loads when there is vacuum. At wide open throttle, there is no vacuum, which is where we are all looking for max performance without pinging. He said vacuum advance is for efficiency and gas mileage only, and with a light load, an engine will take as much advance as you can give it, over and above your initial+centrifugal advance. This is why lots of racing distributors don't even have a vacuum advance. They are always "on the throttle" and have no use for a device that advances the timing when "cruising".

 

Good catch! Didn't mean to confuse anybody-should really preview these things before I post 'em! Sorry 'bout that and thanks for the correct info, just came back to straighten it out now that my brain finally caught up with the rest of me, for a little while anyway (weekend camping thing) but darn it, you beat me to it! Was hopin' to fix it before anyone noticed (yeah, right)-you folks are just too sharp for a Monday! (It is Monday, isn't it?) But-Thanks again! Chuck

 

since you mentioned the springs...

should the springs be the same size? i have two different sized springs on my distributor- (previous owner)

thanks,
sam

 

One spring shold be heavy and the other much lighter. Reason is at low rpm's the advance needs to come in quick but as the engine rev's higher the advance rate needs to slow down.

 

My wife got home and she could then step on the gas and read the tach for me. Here is what i found. At 500 rpm , idle with vacuum plugged, the timing is 12% btc, @1000 rpm 30%, @1500 rpm 32% and the advance tapped out at 2000 rpm 38+- %. Seems to me from what I am reading that this sucker is in the zone. What does the jury say?



1971 F-350 1 ton dump, ground up fully restored w/ 360 motor