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 Hood tach with HEI
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Tribal Scout

13 Posts

Posted - 13 Jul 2017 :  2:00:31 PM  Show Profile  Reply with Quote
I have a 1969 Trans am (clone) with factory hood tach. I replaced the original with a reproduction. I believe it to be a OER. But 100%. I bought it 6 years + and i am not home now to check. I use it with Pontiac HEI with no issues. Works flawless.

After installing my new 461 stroker engine and a few trips to the track. I thought i would be a good idea to install a rev limiter, but wanted to keep the HEI.

I purchased a MSD Digital GM High Energy Module with Rev Limiter MSD-83647. Once installed the car would not start. Checked for fire and there was none. So I sent back the module and put back the stock module, and the car was running fine again. Once the second module arrived, I installed it, and the car fired right up. Then I found my hood tach was dead. This module is real simple to install, but I checked the instructions just to be sure. I had the grey wire go directly to the tach wire as stated.I then tryed installing a after market sun-pro RPM gauge to see if it would work. This RPM gauge worked but the RPMs were way out. I crossed referenced it with my timing light, and there was a 700 rpm discrepancy, at idle. At higher RPMs it was way out. I then purchased another tach, and tried it. This one was also out, but this time about 500 rpm at idle.

I decided to remove the MSD module again, and installed my GM module. Now things are back to normal and my hood tach works, but I still don't have a rev limiter.

Has anyone else tried this module with a HEI and hood tach? I see Mallory also has a similar product. Perhaps this one will work with my hood tach? I thought about going with a MSD ready to run distributor and coil. But that is a large investment. I would also have to purchase another 5.00 distributor gear to match my HR cam. Would that distributor give me the same issues with my hood tach as well?

If anyone has had the same issues I would look forward to hearing from you and any possible fix.

Rick Hickey
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