flathead ignition
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Timing Page #2
Some more discussion regarding the timing on the Flathead; This one is from "Hoop" on the Ford Barn
Re: Flathead timing update on site ...
A bit of confusion.
A bit of confusion.
"Are you sure about the 8 deg being on the dist and 16 on the crank,
Does not ford info talk about 4 deg. Lawrie"
"Degrees" measure several functions on the helmet and crab distributors. First you have dwell that is determined by the opening and closing of the points. Then you have two types of advance, one which is controlled by weights and mechanically changes as you accelerate. The other is Initial Advance that is adjusted at set-up and remains unchanged during operation.
Lawrie's question mixes two different degree functions. Yes, 8 degrees of mechanical advance means the weights will add up to 8 distributor degrees OR 16 crankshaft degrees as the engine revs up. The later 11A will add up to 11 dist or 22 crank degrees. The crank turns 2X for every 1 distributor rotation.
How about the 4 degrees? That is Initial Advance that is permanently set during the distributor set-up. As mentioned:
"I always set the drivers side points with a K.R. Wilson timing fixture in order to get the initial timing correct. (How do you guys set the timing or are you just guessing?? Do you just set the distributor timing mark to the center position and hope for the best. V8fordman."
That's a statement not a question. V8fordman is right on the money.
If the L.H. (left-hand) points dwell is set correctly, placing the Index slide in the center normally has the distributor firing at TDC ... top dead center ... not 4 degrees of Initial Advance. 4 degrees may not seem like much but it represents up to 20% of your Total Advance ... the combination of distributor mechanical advance and Initial Advance.
"... with no dist machine I just set points .015 they always run fine but it's nice to set em up in a machine. Walt"
Original instructions called for setting the points with a feeler gauge. Points/dwell are about TIME. It's expressed as degrees of rotation, but it's really about how much time the coil has to saturate/charge. If you run at 4000 rpm the coil has very little time to charge between plug firings ... dwell is critical. If you are turning 2000 rpm, it’s not so critical.
If you set the points at .015" and get the Initial Advance at the prescribed 4 BTC, like Walt you will find that you'll run fine. The Initial Advance IS more important no matter how you set it ... including using Bruce's "field expedient" ruler method.
Normally, if the points are set correctly, the Index slide will be one notch counter-clockwise from center ... not centered. No matter what, it needs to be set on each distributor. Each notch represents 2 distributor or 4 crankshaft degrees. This means that on an 11A distributor you can expect 22 degrees of mechanical advance PLUS 4 degrees for each notch. If you want more than 34 degrees (!) at the third notch, you can fiddle with the point gap and squeeze out a little more advance.
Standard documentation, for example Ford and KRW, refer to the points as L.H. or R.H. That means Left or Right as seated in the vehicle. "Driver" or "Passenger' side can be problematic if the vehicle is right-hand drive.
Most of this is just simple Math but does require some explanation. Do your own testing and check out my comments.
Join Date: Sep 2010 ( From a discussion on Vacuum advance)
Posts: 406
[Default] Re: Converted SBC distributor - Vacuum advance or not?
Vacuum advance is a colloquial term that car guys just say in reference. I didn't read every reply and I'm sure the replies have gotten really deep based on some that I did read, but simple and basic never lets you down. Depending on where you source the vacuum it's more a load compensation device rather than additional advance. You can surely set it up for additional advance but i always felt it worked best th other way, to repeat, a load compensation feature. You tromp the pedal, vac drops, timing is retarded a measured amount to assist in reducing detonation. As engine speed and vacuum increases so does timing. It has to be hooked up to "ported" vacuum to add more timing. Generally speaking there's usually no need for more. Initial timing is usually set low for those equipped with vacuum pods, then once vac is applied it advances. All mechanical has to deal with engine speeds and initial settings and there's no load compensation in play. The intended use should dictate the need.
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