Duraspark II recurve clarification needed.

[Anonymous]

Going to step up to a DSII this weekend (after having found out that I'm running a L-O-M dizzy with a Holley 1940 that has no SCV... *sigh*).

I want to do the recurve procedure set out in the "Dramatically Better MPG" sticky. Lots of good info in that sticky... but it is manifestly unclear which spring is the "lighter" spring. Here's my DSII:

When I rotate the reluctor plate, the spring on the right is already fully engaged (i.e. no slack). The spring on the left has some slack and it does not "catch" until the plate has moved a little more than halfway along the 13R slot. For clarity, I'm going to call the spring on the right the "primary" spring since it is engaged for the entire travel of the plate. The other spring, that engages later, I'm going to call the "secondary" spring. (Someone please correct me if this wrong.)

The $64M question: Which spring is the "lighter" spring?

 

[addo]

I would say it's the one on the right. It has a greater coil diameter, which translates to a longer wire, meaning the tensile force is translated to torsion over a greater distance.

 

[Anonymous]

I would say it's the one on the right. It has a greater coil diameter, which translates to a longer wire, meaning the tensile force is translated to torsion over a greater distance.

Precisely the type of response I was looking for! This is what I had determined to be the "lighter" spring, but the "Dramatically Better MPG" sticky above has a post therein (apparently from "Guest" the original poster) that states that the lighter spring is the other smaller coil dia. (here's the post from the sticky):

inside the dura ll

maybe some one could give a line nice draw to this for howto .

Well, I don't know how to draw on that, but the one you want to change is the lighter one, which appears to be the one on the left in this picture. The arm that supports the OTHER spring should be bent slightly toward the center of the distributor, so that the post in the advance plate rests halfway up the "slot" of the spring.

Sorry to be gone from here so long...

... this just didn't make any sense to me based on my observations of the advance mechanism. Thanks for the clarification, Addo!!

I wonder how many persons tried this mod and had it fail because they removed/replaced the wrong spring??!??!

Anyone else want to chime in here about the viability of this mod?

 

[falcon60]

Addo is correct...the spring on the Right is the "lighter" one. It controls advance during the 1st half of the range,then the heavier spring contacts the arm and adds resistance as speed increases. The nice part of this mod is that you can later access both springs by rotating the engine until they are visible in the hole in the breaker plate,and can even bend the posts to change the advance rate if need be (without taking anything apart on the dist). I'm running one on the 200 in the Falcon,using the 13* setting and have tweaked the springs to get the rate of advance that works best without pinging.

Terry

 

[Anonymous]

Many thanks gentlemen!

 

[wsa111]

The stock duraspark advance curve is a joke.
Purchase a light spring kit from summit & then check out this link.
If you do not have the expertise to do the following, contact them for a fully modified curve to match your engine combinations.
http://www.reincarnation-automotive.com ... index.html

 

[mugsy]

"Light" refers to the spring force. The force a spring develops is closely related to the diameter of the wire used. Look at the wire diameter; not the diameter of the coil to determine which one is "light". Coil springs work on the same principle as a torsion bar. The "spring" is actually the wire twisting. The smaller diameter wire will twist easier than the large diameter wire. I know in sizing torsion bars the spring rate or stiffness is proportional to the diameter of the bar to the 4th power.

tanx,
Mugsy 8)

 

[Bort62]

Well, I certainly changed the spring on the left.

Seemed to have some weird timing issues - I wonder if that is the problem.

hmmm.....

 

[JackFish]

I too changed out the heavier spring, meaning the one with the larger diameter wire. Much better highway performance up around the 3000-3500rpm range compared to stock. I believe it would allow full advance to come in sooner.
I have no complaints about the drive-ability of this setup, works really well for me. Although I might switch to the 10* slot, since I also have the cam advanced 4*, and under extreme load I do get a little ping.