timing changes with rpm

[Jim Comet]

Hey all, I have a locked out MSD distributor on my 416FE. I am running a Pertonix 510 ignition box and matching coil. My solid roller cam is new as is the Crane cams distributor gear. What I am experiencing is, when I set my timing to 32deg at 1000rpms and then rev the motor to 3000 plus rpms I loose 4-5 degrees of timing at higher rpms. Any Ideas what would cause the ignition to retard at higher rpms? I do run an MSD timing advance/retard that I can control with a dial on the dash. I have tested the ignition system with and without it hooked up and it makes NO difference. Could it be a faulty MSD pickup? Or would most likely be in the Pertronix box itself. Any thoughts or ideas are appreciated. Thanks, Jim

[GerryP]

You can see this when you have loose bushings in the distributor.  It's not likely to be the magnetic pickup itself because that outputs based upon the reluctor moving through the magnetic field.  The ignition module is looking for the signal to rise, peak, and start to fall as the trigger point.  If the reluctor changes position, then so does that sine wave.

[Joe-JDC]

Timing chain stretch can cause this problem.  Also, MSD boxes are different between boxes.  Mine was 4* different.  Joe-JDC

[Jim Comet]

Thanks for the responses. It has a new timing chain. It happens very consistently. I have a test day coming up so I think I will go up 1 degree at a time for base timing and make a couple passes and see how it likes it. I'll go up till it slows down and back it off to the sweet spot. Jim

[6667fan]

Jim, I read through the 510C instructions and did not see anything that mentioned the unit pulls out timing up top, either via an adjustment or built in.
I would like to hear more of your impressions of the unit. Another MSD box puked out on me so I’m considering a different manufacturer’s box.

Looking around on the web a SBC owner was experiencing a similar problem. Turns out his Cloyes timing chain was moving due to not enough pre-load on cam button. His small block’s timing cover was flexing.
Good Luck at track

[Jim Comet]

Talking to people in the industry it sounds like it is a thing when using a magnetic pickup distributor. As far as the Pertronix box goes, I really like mine. I actually have the discontinued 520 box that I can run with my smart phone. The 510 box is the same functionally as my 520 box except it uses rotary dials to make the changes. My brother has the 510 in his Maverick and really likes it. I have been running my Pertronix since 2018 and it has been very reliable. I rely on it for the start retard with having locked out timing and the 2 step for launching. If something would happen to my current box I would probably by the 510 box to replace it although the new MSD ultra 6 appears to be a functional duplicate of my 520 box and would consider it if not for all the MSD issues people are currently having. I wonder if percentage wise if MSD boxes get a bad rap because there are so many in use compared to other brands of ignition boxes? Jim

[6667fan]

So if you have to keep adding in timing to compensate for the loss you might have to go to 37/38 degrees? Utilizing the max amount of retard in the 510 will get you down to 19/20 degrees at start. Is your MSD retard unit able to pull out more than 18 degrees?

Do you have a stock distributor to swap in, just to rule out the MSD one as the culprit?

[Jim Comet]

I don't have an extra distributor. I do have a new MSD pickup I could change in if needed. With 13 to 1 compression I am surprised my stock starter has never struggled. Must be the good battery and 0/1 cables. Jim