ignition timing curves

[41/53dodges]

Does anyone have a graph of the timing curves on our flatheads? I'm working on some computer stuff now and need to see the curve. Thanks!

-josh

[John-T-53]

I was looking for the same thing when I rebuilt my distributor last year with a Pertronics solid state unit. Couldn't find anything other than what the shop manual says:

 

Initial timing: TDC

 

Maximum mechanical advance: 18 to 22 degrees at 3200 RPM

 

Max vacuum advance: 18 degrees

 

I tried to have a couple shops in my area test my Distributor on their Sun machine, but they couldn't get it to work with the 6 volt + ground setup.

 

So, I've been meaning to chart the advance curve with the dizzy installed on the engine using a tach, but haven't got around to that yet....need to get a 6v tach first!

[TodFitch]

On the car side, the 1936-42 factory shop manual has some numbers. Looks pretty similar across those years. Here is the data for 1942:

 

Mechanical advance:

0° @ 350 RPM

3° @ 400 RPM

5° @ 620 RPM

8° @ 940 RPM

10° @ 1150 PRM

 

Vacuum advance:

2° with 6 3/4" of vacuum

8 1/2° with 15" of vacuum

 

Looks like they went with a lot more advance post war, the 1946-54 factory shop manual shows less detail but more advance. For the P15:

Mechanical: 16° to 20° at 2050 RPM

Vacuum: 15° to 19° at 16" of vacuum

[41/53dodges]

Sweet, I should be able to work with those numbers. I never realized just how much advance these motors ran with.

Thanks guys!

[greg g]

There were several different distributors used each had a little bit different curve.  I had 4 distributors, 1 from 46, one from a 48 Dodge, one 54 Dodge truck and one 56 plymouth 230.  I took them in to the college where I worked and had the folks in the auto tech program fun them on their old Sun dist machine.  The one from the 54 truck most closely matched its factory numbers so that what I am running.  As Todd said the later ones had more initial advance and more advance through the range.  I would imagine it was the result of better gas and higher compression ratios coming with the passing of years.

 

The most interesting part was watching the 20 something year old kids checking out the disributor and trying to figure out the workings.  most had never seen one except on tractors and such.

[Don Coatney]

 

 

I tried to have a couple shops in my area test my Distributor on their Sun machine, but they couldn't get it to work with the 6 volt + ground setup.

 

 

Advance curve does not care about voltage nor polarity. It only looks at when the mechanical or vacuum advance starts and stops.  I do not understand why any shop with a Sun machine would not understand this.