"Dramatically better MPG... Duraspark II" confusion

[mysavioreigns]

This sticky (which is also over on Classic Inlines) has, what I believe, is some incorrect information which could cause heartache.

After reading an exhausting 17 page guide to Ford's Duraspark Ignition Timing, I am thinking that the sticky above is incorrect in the statement:

1. Remove the lighter of the 2 springs in the DII and replace it with one of the #925D springs.

There are 2 springs controlling the centrifugal advance in the DSII Distributor, and (most of the time) one has a thicker wire diameter than the other, and therefore requires more force to stretch it the same distance. If the thicker wire is replaced with the Mr. Gasket #925D spring - a much thinner wire diameter - it would require less speed to achieve the same advance. Simply, it will take less time to reach a higher advance.

Here's a picture of the thicker wire [top left] vs. the Mr. Gasket #925D [top right]

here's a larger image

Now, for the panel's approval :mrgreen: Is that what others understand this as, also? I know Jackfish commented in the original sticky that he believed it was wrong, and he had replaced the thicker wire, not the thinner, and had successful results.

Now, on to part 2 of the Duraspark Ignition Confusion...

2. There is a support arm that holds the larger spring, on it's non-slotted end. Bend this arm in toward the center of the distributor, just 3/32".

The thicker wire diameter will frequently have "slack" in it, from the factory. This means it will take slightly longer to engage tension in it. A chart of the advance would rise, and once the thicker spring is engaged, it would flatten out some. I'm not sure if, when Mark P wrote this Sticky, he was saying that you need to create an even more "slack" state, or if he was conveying that it should just match up to like Ford had intended when they left it "slack" from the factory.

Hope that makes sense to everyone. I'm trying to increase my level of understanding on these engines and in the process of doing so, I want to make sure I don't do things "just because someone said it will make it better" but because I really want to understand the engineering and logic behind it.

I'll have more questions, I'm sure. But I'll wait until we have some feedback.

Thanks
Stephen

 

[wsa111]

Stephen, the only way to be certain is do the spring installation with the aid of a sun distributor machine.

That is the best way to check when the advance starts & stops advancing & how much total advance you have. Otherwise you are just guessing.

You can use a timing light & tachometer if your damper had degree marking on it. The other option is a dial-back timing light. Not recommended if you have a MSD box. Bill

 

[mysavioreigns]

Once the springs/slots are installed and the initial timing is set, you should be able to check when the advance begins and what degree it is at by plotting a graph measuring the advance readings (via the timing marks) vs. the RPM, increasing the RPM by 500 each time. This will give a close estimate as to what the timing cure will look like.

Of course that will require adding tickmarks to the pulley, because I think most go up to 15*, and that is not going to be enough when you get into the higher RPM ranges. Luckily that isn't too difficult. At least it's cheaper than a Sun Dist. machine

 

[66 E100 Pickup]

Stephen, I believe both you and the Classic Inlines sticky (not your link, but the photo guide http://classicinlines.com/DSIIswap2.asp) are correct (according to my interpretation).

While it is confusing to use two arrows in a photo and make two comments regarding those arrows, the top arrow clearly points at the spring, and the bottom arrow points at the arm. This matches the description of the springs also.

John

 

[mysavioreigns]

John,

Thanks for the reply, I agree it is pretty confusing with the arrows. I'm still seeing a problem though; that article says to replace the lighter spring (appears to be green arrow) with the #925D spring.

What I'm thinking is correct (as well as Jackfish and a few others) is to replace the heavier spring (the one near the red arrow) with the #925D spring. I'm not 100% sure if this is correct, but to me, doing this would make allow you to achieve a higher timing advanced quicker.

 

[mysavioreigns]

Well, after more consideration, I think I might change my own stance

After a little bit of bench testing, I believe that replacing the heavy spring with the #925D spring will not result in a better timing curve. Here is why:

The varying spring thicknesses, with the thicker spring having "slack in the line" will create 2 distinct timing curves, which result in a faster increase of the curve, then will level off a bit to a slower increase in the timing advance.

My original plan, I believe, will achieve the maximum advance MUCH quicker, thus actually hurting the higher RPM mileage/power. Now that I'm putting the thicker spring back in, and switching the lighter spring (as the sticky originally said), I will focus on the slot. I was running the 15R slot but have switched to the 10R slot. This will change the total mechanical advance from 30* to 20*, thus I will need to increase my initial advance by 10* to compensate. That should greatly help the engine.

I'll have to update when I get to do some real testing on it.

 

[FalconSedanDelivery]

WSA is Correct , nuff said