Tachometer vs HEI Limiter
Posted: Fri Jun 26, 2020 3:50 pm
New engine mated to an old ford c4 transmission.
Using Petronix D72000 hei module with built in rev limiter.
New engine was broken in on an old duraspark ignition and ran about 1000 miles without problems using duraspark.
Installed HEI on car and set hei rev limiter to 6500 rpm. Car runs great and has run great for 3000 miles on new engine.
Car has an air shifter activated by the shift light from the 30 year old Mallory tachometer. It has worked great for years.
Set shift rpm to be about 5900 rpm...shifted perfectly about 20 plus times...never really looked at the tach.
Decided to up shift point to 6100 ... seemed to run against the rev limiter before the shift occurred.
Pertronix says the hei limiter should be +or minus 50 rpm from set point.
Reset hei rev limit to 6400... it acts the same.
Plugs look good but changed them any way. Acts the same. Checked wiring and added an extra ground. Acts the same.
I have played around with lowering the shift point to 5000 and even 4000. The shift point works to within 100 rpm based on me and my son watching the tach.
I tried comparing the Mallory tach to a cheap tach with both attached to the negative of the coil together,they did not agree well at all. I doubt the cheap tach.
The Mallory tach seems to act like it always has.
How can I verify that my Mallory tach is reading true and that my shift light is reading true?
Using Petronix D72000 hei module with built in rev limiter.
New engine was broken in on an old duraspark ignition and ran about 1000 miles without problems using duraspark.
Installed HEI on car and set hei rev limiter to 6500 rpm. Car runs great and has run great for 3000 miles on new engine.
Car has an air shifter activated by the shift light from the 30 year old Mallory tachometer. It has worked great for years.
Set shift rpm to be about 5900 rpm...shifted perfectly about 20 plus times...never really looked at the tach.
Decided to up shift point to 6100 ... seemed to run against the rev limiter before the shift occurred.
Pertronix says the hei limiter should be +or minus 50 rpm from set point.
Reset hei rev limit to 6400... it acts the same.
Plugs look good but changed them any way. Acts the same. Checked wiring and added an extra ground. Acts the same.
I have played around with lowering the shift point to 5000 and even 4000. The shift point works to within 100 rpm based on me and my son watching the tach.
I tried comparing the Mallory tach to a cheap tach with both attached to the negative of the coil together,they did not agree well at all. I doubt the cheap tach.
The Mallory tach seems to act like it always has.
How can I verify that my Mallory tach is reading true and that my shift light is reading true?