Timing, where are you?

[Jeff73Mach1]

no, I didn't realize it was all electronic on your car. You are probably right under that circumstance. In a distributor, the mechanical weights and the vacuum advance both move the plate the point, or the electronic pick up are mounted to. The plates have a slot that allows them only so much movement. Vacuum advance plus mechanical advance works until the limit is reached and then no more advance occurs. the plate doesn't care whether 10 degrees comes from vacuum and 20 comes from mechanical or the other way around it is just two different mechanical ways to move the same plate.

 

[barnett468]

.

The mechanical advance and points pate are totally independent.

If you have 10 initial and 20 from the mechanical advance you have a total of 30.

You then add how ever much the vacuum advance ads to the amount above, so if the vacuum can adds 10, you then have a total of 40 when both the mechanical and vacuum advance are at their max limits.

If your mechanical is all in at 2500 rpm, and you are on a flat or down hill road at steady throttle, it is possible for the engine vacuum to be high enough to cause the vacuum advance can to provide the max amount of timing it is set to, therefore, if you have 30 mechanical and 10 from the vacuum can, you would then have a total of 40 degrees of advance at only 2500 rpm which is typically too much which is exactly why they make adjustable vacuum cans.

.

 

[Jeff73Mach1]

well. I guess I'm wrong. Learn something new every day

 

[vozaday]

When I was working on my car after everything was done I found a local guy to look over the car. First thing he did was ask for my cam spec sheet. Took off the distributor and set it up to match the cam. He also discovered the vacuum advance wasn't working so he set it up to compensate that. Car runs great. He builds and races front end dragsters.

Point of the story is that if you have modified your engine it may be worth while to take it into a performance shop and have the small things like your distributor dialed in.

 

[Jeff73Mach1]

Good point. When I built my engine I had mine set up by a very talented drag racer, along with my carb too. WHile I can do some basic tuning on them, I cannot do the fine detail work that he does so easily.

 

[jbojo]

Yeah, thx for clarifying guys. Been doing a lot or research on the subject and it all makes sense to me now. My system is computer controlled and the distributor has no weights, springs or vacuum linkage. I am able to just adjust all the settings from a handheld controller and can precisely indicate when and how much timing to apply and then watch it all as the engine operates.