Distributor Curve

[1bad6t]

I have been playing around with swapping springs and bending tabs in my Dura-spark II to get 32-34 degrees total advance in before 3000 rpm. Here is a chart I made showing the curve. My question is this too much of a jump or does it look normal? I have a 74 Maverick with 250/C4/2.79 gear. Only other modification is ‘69 timing set and emissions have been stripped. As far as I can tell within the few miles I drove with this setting no spark ping or rattling. I will be going with a Crane adjustable vacuum canister once I get the mechanical advance curve where it needs to be.

http://1bad6t.com/Maverick/RecurvingaDu ... chart3.jpg

 

[JackFish]

Could you be more specific as to the spring swap?
Which one, where? Or both?

I swapped the heavy secondary spring, and left the primary spring stock, and had a curve that was in between the two modified ones you have but still ended up with a peak similar the red line.

Is 29 degrees of advance not somewhat high @ 1500rpm?

 

[1bad6t]

I replaced the heavy spring with the (original) light spring and put a #925D spring where the light spring use to be. I bent the heavy spring tab in 3/32”

I was under the impression that both springs work together and it doesn't matter where the spring lives...it is the combination of both springs that is holding back the centrifugal force that is swinging the weights. I can see where the distant between the anchor tab and pin will play a part in the spring rate. Correct me if I’m wrong assuming this.

The 29 degrees @ 1500 is what has we wondering. I was expecting something around 22 degrees.

 

[JackFish]

When you "heavier" do you mean the primary spring or secondary?
In my estimation, the secondary spring is the heavier due to the thicker spring wire, and it is usually a little loose on the tabs in stock form. I was happy with the intial curve of the primary spring and only replaced the secondary with the light 925D. This allowed a stock curve initially, and then a faster ramp up to full advance.

 

[1bad6t]

We are on the same page with our spring terminology. I replace the secondary spring with my primary spring and used the 925D. This is where I messed up. I will go back and swap springs and update my chart with my findings. Thanks for your reply.

 

[1bad6t]

I put the secondary (heavy) spring back in...now I have 26* @ 1500. I also lost 2* from there on out.

http://1bad6t.com/Extra2/chart5.gif

 

[mugsy]

I was under the impression that both springs work together and it doesn't matter where the spring lives...it is the combination of both springs that is holding back the centrifugal force that is swinging the weights.

(OK how do you copy someone's quote? this is totally torking me off!!!!!!!!! :x )

Is this true? I was recently playing around with the spring and curve thing and noticed that the springs were on different positions than the photos of this upgrade. I had an old LoM dizzy that had a ton of problems and found out the the springs were on the wrong posts, it delayed any advance for a long time...

 

[FalconSedanDelivery]

It matters on a Loadamatic , but NOT on a points/duraspark with Vac adv

 

[mugsy]

It matters on a Loadamatic , but NOT on a points/duraspark with Vac adv

Groovie!! thanks for the info. Now back to your regularly scheduled thread.