[C2] Dwell Changes with RPM?
07-13-2018, 01:56 PM
#1
Burning Brakes
Thread Starter
Dwell Changes with RPM?
While setting timing I noticed that while I had set the dwell for 30 degrees, it gained a degree or two with increased RPM, then settled back at idle.
The points have less than 1500 miles on them, are positioned properly and the screws are tight. I've checked this with two different dwell meters.
Normal??
The points have less than 1500 miles on them, are positioned properly and the screws are tight. I've checked this with two different dwell meters.
Normal??
07-13-2018, 02:04 PM
#2
Race Director
While setting timing I noticed that while I had set the dwell for 30 degrees, it gained a degree or two with increased RPM, then settled back at idle.
The points have less than 1500 miles on them, are positioned properly and the screws are tight. I've checked this with two different dwell meters.
Normal??
The points have less than 1500 miles on them, are positioned properly and the screws are tight. I've checked this with two different dwell meters.
Normal??
You can blueprint the distributor and perhaps make things better...............but not certain your car will notice the difference.
Years ago I used Mallory Rev-Pol and ACCEL racing distributor to correct this kind of issue, including some spark scatter. But in truth, although everything looked and functioned better, the 1/4 mile times really did not show it.
FWIW.
Larry
Last edited by Powershift; 07-13-2018 at 02:06 PM.
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After38Years (07-13-2018)
07-13-2018, 02:31 PM
#3
Burning Brakes
Not typical. I run a Delco vacuum advance distributor with points and dwell stays rock-steady at different rpms. Maybe bad bushings and/or too much end play.
07-13-2018, 02:32 PM
#4
Race Director
You could have some bushing wear although if so, from your description it's probably not too bad yet. Bad bushing wear will result in dwell jumping all around as the motor is reved up although at idle it may be relatively stable. Or it could just be some variation as the centrifugal advance starts in due to the points plate movement. On a Plymouth I have, plugging in the vacuum advance after setting points results in a 2 deg change in dwell because of how the points plate is hinged to move when the vacuum can pulls it - it's not concentric with the shaft.
As long as it's just a couple of degrees and not jumping around randomly it's probably not worth losing any sleep over. But if it is bushing wear it will eventually get worse and start missing at higher RPM and require fixing.
As long as it's just a couple of degrees and not jumping around randomly it's probably not worth losing any sleep over. But if it is bushing wear it will eventually get worse and start missing at higher RPM and require fixing.
Last edited by DansYellow66; 07-13-2018 at 02:35 PM.
07-13-2018, 04:18 PM
#6
Race Director
07-13-2018, 04:23 PM
#7
Race Director
Member Since: May 2000
Location: Redondo Beach USA
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The GM spec for dwell variation is +/- two degrees. Normally it will drop off a bit at high revs, especially on SHP engines if you are not using the proper point set. However, on these ancient distributors cam wear may be an issue on some.
Duke
Duke
07-13-2018, 10:37 PM
#9
Burning Brakes
Larry - As far as I know, my distributor is completely stock. I reconditioned it and shimmed the end gap, set dwell at 30* and it has always stayed consistent for the 15 years I’ve owned it. Only variation is when points wear down, affecting the dwell. I’ve never had one vary like the OP is experiencing.