Testing the HiRev 7500
Bill Jones posted some of his tests of timing retard in this thread.
He's calling it hysterisis. The phenomenon is the same even if at that point he didn't know the full cause.
[URL][URL]https://www.speed-talk.com/forum/viewtopic.php?f=1&t=22331[/URL][/URL]
And here in the middle of hte page he describes how the factory (GM) compensated for slew in the distributor.
[URL][URL]https://www.speed-talk.com/forum/viewtopic.php?t=22643&start=15[/URL][/URL]
More discussions on slew.
[URL][URL]https://www.speed-talk.com/forum/viewtopic.php?t=14367[/URL][/URL]
and this one with some of the 'retard built in' history bubbling into the light.
[URL][URL]https://www.speed-talk.com/forum/viewtopic.php?t=36678[/URL][/URL]
Reading through those is amusing and sad.
This has been known for decades and there are people that argue this to the death and they still get it wrong.
In thinking about it today, the electronics in my machine have to be at least as fast or faster than any box I’ve tested because with points I see zero retard. At really high RPM I might see a degree of retard but I don’t know if you can blame the points for that retard, the machine or if it’s just the nature of the electronics.
If the electronics were slow it would show up in the points too wouldn’t you think?
It’s not cam walk. It can be an issue with timing but that’s a different symptom. And what about the Chrysler small block and the Fords that use a cam retaining plate? That’s a bit of a bugger there.
The shitty GM advance and the sloppy way they drive the distributor certainly contributes to spark scatter but that is not part of the equation on a test bench.
Timing chain slop is another phenomenon that gets thrown around when timing retard happens. Again, this contributes to spark scatter but there is no timing chain on the test bench so that’s a non factor as well.
Guys that use very light springs to get the all in timing as quick as they can exacerbate spark scatter all the more with those light springs.
At idle speed the pulsations of each cylinder firing actually causes the crank to slow down and speed up. This makes the timing jump around at idle. That’s why most clutch discs have springs in the hub. To absorb those pulses and eliminate or at least reduce what some call clutch chatter to a minimum.
Combine that with a timing chain, the shitty GM advance mechanism and the way GM drives the pump it’s no wonder spark scatter is real.
It’s time people start learning this and fixing the real issues so the engine they paid all that money is at least making the best power as it can.