Dizzy Modification



I've followed CC's dizzy saga for sometime now and alot of what he was experiencing I had experienced myself (but not that much advance ;) ).

I've solved my problems (after several weeks) but I came across this website one night that looked interesting. I don't think I want to try this but I am going to be installing a 2BBL to the log soon and I know I'll have to go through the whole vacuum adjustment procedure again anyway.

Sooooo....should I try this or not? Or should I just leave well enough alone?


Hi, Stang;

All Ford distribs have this feature. My Fairmont's 3.3L six has 11 and 13 degree slots, my T-Bird's 351W has 10 and 15 (like that guy's shows) and my '67 390 stock distributor has 13 and 18, while the Police Interceptor unit I'm now using in it has 11 and 15 degrees.

Instead of changing the slot and trying to optimize the timing vs. performance vs. gas mileage, etc., you might consider this instead: Go to a junkyard and collect some springs of different strengths from other Ford distribs. If you want quicker low end pickup, like most of us do, use lighter springs on both sides of the whirly weights. However, if octane is low in your neighborhood, this can cause pinging at lower speeds than you might like. In that case, use a lighter spring just in place of the heavy spring (every distrib has a light one and a heavy one). This will bypass the "flat" part of the curve at around 1500-1800 RPM, shifting it downward to around 1300-1500 RPM. This will feel real good just before that point where these engines run out of breath because of the intake log, so it will seem more responsive. Here in the mountains, it really helps on curving, steep mountain roads. The need for higher octane is less pronounced with this second approach as well.

One other thing: the heavy spring usually has a long slot on one end that lets the lighter spring extend before the heavy one gets involved. Be sure to tailor your new lighter spring to match this slot or the results will feel strange. It would then cause a LACK of advance at about 1500 RPM until you reached about 1800 RPM, when the advance would start in again. Since these engines start to get asthma at about 2500 RPM and up, this would not help you out any.

Write down all your original settings, too, just in case...
Thanks Mark!

I'll try changing springs first. If that works out okay....I'll LEAVE WELL ENOUGH ALONE. ;)

This discussion has omitted the effect / impact of the vac system. If you take the time to set the mechanical up properly, as outlined in the web page as the proper way to achieve "condition C", you could (and I did) elimimate the vac advance system.

Specifically, the vac system adds to total advance under a no load condition, i.e., idle (we all know how much the 200 I6 likes advance at idle), and cruising down the road. The added advance was used by Ford (and others) as a means to reduce NOX emissions, and improve mileage (I can't confirm either one but that was the party line). The overadvance condition is eliminated under load (accelleration and hill climbing) as a result of the fact that manifold vac is reduced under these conditions so the all-in advance was reduced to a level that would prevent ping. Keeping in mind that they had better gas back then, and the fact that you can't predict the fluxuation in vac. advance under operating conditions, in my opinion the vac. advance concept is problematic today. If you want to be able to set it and foget it, if you want to be able to predict what the advance curve is going to be under any driving condition, eliminate the vac. advance.

The car likes about 15* initial (idle). Set it at 15*. The car likes about 35* all-in, at about 2500 rpm, under any driving condition. If you set the weights at 10*, you will get 20* of mechanical advance at the crank. The RPM at which this will happen will be influanced by the spring rates, but I don't believe this issue is as important to your enjoyment of the car as the all-in advance amount. Now plug the vac ports at both the carb and the dizzy, and you are done.

As a side note, this method of converting to mechanical only advance is common. It is particularly useful when changing carbs, cams, etc as it produces a totally predictable advance senario.

Enjoy the ride - Steve

I've wondered for sometime now about eliminating vacuum advance. I've also followed MANY posts regarding this modification but, I'm alittle hesitant in trying it myself.

Currently I have only vacuum advance plugged to the carburetor and one from the tranny to the manifold for the smooth automatic shifting. So, if I try to eliminate the vacuum advance all together than I would need to plug EVERYTHING, and set the intial advance somewhere around 12-15 degress, right? Just like you said and forget about it.

I guess it just sounds too easy. After all, sense I bought the car a few months ago I've had many problems just trying to keep it running whenever I wanted to take it for a spin. :LOL:

ANYONE ELSE? Not that I don't trust you Steve but it just sounds too easy. Will I hurt the engine in anyway? What about mpg (give factor for me)? Will I need to put in 93+ octane (we have 105 here near Lambert International :eek: :eek: )?

Thanks again!

Glad to see my problem is now officially a "saga" :LOL: :LOL:

I asked the same question of Tom at Stovebolt. Honestly, the dizzy in the original car didn't have mechanical advance, it only had inital + vacuum.

He didn't seem to fond of the idea, but I still don't see why (esp with my high advance) I wouldn't run just mechanical.

I guess the big question is regarding WOT. At WOT, do you need MORE advance or LESS advance? By running no vac. - at WOT you're going to get the full amount of advance that you have set. By running with Vacuum, you're going to get some amount less than that.
There seems to be some confusion here. Running with, or without vac advance is not critical, either way. My position is simply that if you eliminate the vac advance system you will be able to calculate, in advance, what your all-in timing will be under any driving condition. Up hill, down hill, cruise, WOT accelleration. Also, based on test drives after any modification, you will be able to reset without any doubt as to what the timing is doing.

The goals. First, the car needs enough initial to idle nicely, in gear (stick guys won't appreciate that one). I think we can all agree that this number is in the area of 15* (+/-) with no input from the mechanical or vac systems, i.e., the purpose of slowing the idle down to 500 / 550 and disconnecting the vac lines is to eliminate these elements when setting the initial. Second, there is much evidence to indicate that the all-in advance, the advance needed by these cars over 2500 RPM, is in the area of 35*.

Now, having said that, we all know how to adjust the initial. As for the all-in, the mechanical advance limit in the dual advance dizzy can be adjusted by changing the weight limit in the dizzy, as shown at the web site above. If we assume that we want 15* initial, and 35* all-in, then we must have a 10* weight limit in the dizzy, which will give you 20* at the crank (dizzy advance is 1/2 crank advance - the dizzy turns 1/2 to crank speed). Bottom line, if the initial plus the mechanical will give you the 35* target number, you don't need the vac system. The vac will simply overadvance you at idle, causing you to need to back off on your initial after a test drive. Then, under WOT conditions you may, or may not, get enough advance with you new initial setting. At issue will be how much vac the engine pulling at that specific moment and what does that translate into vis-a-vis advance. Personally, I don't think you will ever know. All I can say is that, according to Ford, the vac will overadvance you at idle, and under a "no load" driving conditions, i.e., when cylinder pressure is low. Their purpose for this technology? Reduce NOX and increase mileage. In my opinion their position has not been verified. The headache of dealing with this now very old technology, on the otherhand, has been verified by owner after owner who has reported timing / idle issues.

Summary, if you want to know what your timing condition will be under any driving condition, if you want to be able to adjust for mods easily, try the out. It's not hard, it's not epensive (if you need to buy a dizzy ask for one with the 10* limit - save some time and trouble), and you will like the results. However, it will be necessary the test drive and adjust the initial up, or down, to get the best results, i.e., the highest initial advance you can set without ping during periods of high cylinder pressure (WOT accelleration - hill climbing).

Enjoy the trip - Steve