Timing Curve

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Mattax said:
All I can say is try it.
I think you know my opinion, but in case not, I'll repeat. LOL
The new timing from 1800 rpm to 2500 may result in pinging during part throttle acceleration and uphills.

You now know how to change it, so you can experiment. No harm, no foul. Just back off the throttle if it starts to detonate under heavy load - that's when there can be serious harm.:eek:
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I forget if the OP has a stick or torque converter but with that curve care needs to be taken to not lug to hard on the engine, especially with vacuum advance. And I'd try to get the VA in shape and working if you can. Maybe bring it in pretty late and maybe take a bit out of it. Any extra timing you can get at cruise will help MPG as long as it doesn't rattle it to death.
 
2500 stall PTC converter.
Haven’t detected detonation yet but haven’t been on the open road either.
I do have vacuum advance with 15* in it.
So I got advice to bring it in a little earlier (which I did) and to get it all by 2500.
So Mattax your concern is that the curve is too “fat” 1800-2500, needing to maybe be flatter there. I might be able to that with more of a difference in spring sizes. More two-stage ???
 
Yes that is what YR and I are both saying.

Can be very annoying. Around 2007 was having this part throttle ping issue. Current engine, torque converter etc. Coming back from St Mary's City in eastern Md. which is about as flat as it gets, with a light rain, really couldn't ask for better conditions to suppress knock. Maybe an hour or two into the drive it was gurgling on every slight upslope or gentle passing of slow drivers. This was all US and state routes too - not interstate.
Looking back at my notes here that was
25* at 1500 rpm
28* at 2000 rpm
30* at 2200 rpm
30* at 2400 rpm up

Even taking two degrees out, it would still sometimes knock at part throttle. Even at an autocross where the engine is not nearly heat soaked.
I'ld have to dig deeper to get the vacuum advance info that went with that. But the point if using vacuum advance for what its intended - part throttle lower density fuel mixtures - then this is the rpm range where its easy to have too much mechanical timing.
It is possible to adjust when the vacuum advance starts as well as its limits. But I think its better to get the mechanical advance a little slower before messing with the vacuum advance.
 
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Understood. I just now saw the arrow you drew on the MSD chart, which is going back to my original springs. But if both are lengthened to get both stages in earlier that should be a safer set up.
Snowing here today, looks like Saturday is the next reasonable day to play with this. I’ll have to find something else to obsess over till then!! :lol:
 
midnight340 said:
Understood. I just now saw the arrow you drew on the MSD chart, which is going back to my original springs. But if both are lengthened to get both stages in earlier that should be a safer set up.
Snowing here today, looks like Saturday is the next reasonable day to play with this. I’ll have to find something else to obsess over till then!! :lol:
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If you really want to go berserk, try changing the weight and/or shape of the advance weights.

Working on a Pertronix distributor, and to get the curve I think it should have, I had to not only change the weights, but modify them.

What a giant PITA.
 
yellow rose said:
If you really want to go berserk, try changing the weight and/or shape of the advance weights.

Working on a Pertronix distributor, and to get the curve I think it should have, I had to not only change the weights, but modify them.

What a giant PITA.
Click to expand...

Who would do that??!!!! LOL (this from a guy who made his own TQ rods in a drill press?)
Hopefully tweaking the springs will get me there.
 
Nice day so finally got to my remote parking lot to try some different spring combos in the MSD. After changing through four different spring combos checking timing on each at 250 rpm intervals ...trying to get it to come in earlier without coming in too fast ...I called it done for the day!! Will post a graph a bit later. :)
 
Results:
The green middle line is the new curve.

BA72DCA2-29B4-4F82-8159-5E2800A9741E.jpeg
 
That might be as good as it gets without reshaping.
Try it out!

If it pings with part thorttle and vac advance hooked up, try delaying the vacuum advance. Or go extreme first. Take the vac advance off and plug the hose.
 
Yeah, tried about every combo I could think of. LOL
It did turn out that one light, one heavy of the silver springs did it ...with some stretch on a loop of both.
So far applying part throttle on some hill has not caused any pinging. I’ll take on the open road for a real test when I get a chance.
 
midnight340 said:
Yeah, tried about every combo I could think of. LOL
It did turn out that one light, one heavy of the silver springs did it ...with some stretch on a loop of both.
So far applying part throttle on some hill has not caused any pinging. I’ll take on the open road for a real test when I get a chance.
Click to expand...
2.5 years later, did the final curve end up working well for you?
 
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