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Need help! I have a 68 with a blueprint motor / /HEI and an OER tic toc tach. Seems to read ok at idle, then way off as rpms go up! Anybody know if a tach filter will solve my problem? I’d also consider sending it out (to whoever?) to have it reworked? Thanx for any help / suggestions!!
 

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There are several solutions out there, the correct one for your application may depend on who's ignition system you are using.
All AC/DELCO original Tachometers and 99% of the reproductions will work just fine with 69 OEM "transistor" ignition option and many folks say that early generation of GM HEI distributors with no modifications. As for the reproductions check the fine print. OER says the same you can expect with an AC/DELCO works for theirs. And in all cases actual experience may vary.

All aftermarket MSD box style and other HEI ignition systems will not work without a filter of some type. All the majors sell filters for their boxes and devices for people using old style analogue signal Tachometers.

There are also third party converter filters and devices, and self made filter plans available. So you have multiple options out there.

In our archives here we have the following threads;

DYI Tachometer Filter instructions and discussion thread:
https://www.camaros.net/forums/19-electrical-wiring/309026-diy-tachometer-filter.html
https://www.camaros.net/techref/electrical/tachfilter/index.htm

Conversations on options of Pre-made third devices, and re manufactured circuit boards:
https://www.camaros.net/forums/19-electrical-wiring/392169-diy-tach-filter-questions.html

If you can't find one in those threads that works for your application post the specs of your system and ignition and someone will have been down that road before and guide you along the way. Not sure Greg is still making these modifications. If not Redline gauge and Speedometer dot com are also good people to rebuilt and retrofit gauges and Tachometers for the modern age.

Brian
 

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I installed a new OER Tic Toc Tach during my 68 SS/RS L48 build. I also built and installed a DYI Tachometer Filter mentioned in 69-Pace’s post. Everything worked well, I had installed a Pertronix Ignitor ignition conversion in my distributor, car was running on battery only. As the build progress the full electrical system was finished and the rebuilt stock alternator was installed it fried my new tac. I had to pull it back out and send it off to be rebuilt to handle HEI, lesson learned.
 
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