# HEI ignition & Rally tach



## TommyG67 (Dec 17, 2009)

Does anyone know if I can run a Rally instrument panel tach directly from my HEI ignition? I converted my '67 GTO to HEI and am very happy with that, but have since aquired a Rally instrument cluster and wonder if the tach will work OK when connected to the HEI tach output. Mostly, I don't want to fry the tach!


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## FlambeauHO (Nov 24, 2011)

I'll stay tuned on here because my 68 rally tach has never worked with my HEI. I always assumed I had a bad rally tach and was planning on mailing it away during my rebuild.


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## Matthew (Feb 11, 2011)

Your tach will have to be upgraded for electronic ignition. Several places that will do it -- Auto Instruments did mine. Cost was about $275. Matt


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## Eric Animal (Oct 28, 2007)

I THINK, there is a "box" that you can purchase from MSD that will allow a stock tach to work with electronic ignitions...about $50...and tells you what it will work with....check it out. Eric


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## SIXT5GTO (Mar 9, 2010)

The HEI that was in my car had a hook up on the side for input 12vlt power and a tac, I hooked tac wire up and it worked,( there is a fuse in the tac line, it never blew) So it can work with the right model distr.
Hope that helps


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## BearGFR (Aug 25, 2008)

SIXT5GTO said:


> The HEI that was in my car had a hook up on the side for input 12vlt power and a tac, I hooked tac wire up and it worked,( there is a fuse in the tac line, it never blew) So it can work with the right model distr.
> Hope that helps


:agree I have an aftermarket Proform HEI in my 69, and it has two connections on the cap -- one for 12v in (ignition) and the other for the tach. I connected my in-dash Rallye tach directly to the tach lead on the HEI, through a fuse, and it works. I'm not convinced the caibration is accurate though - it seems fine at idle and low rpm, but up around 5-grand or so I think the tach may be reading low. The other evening I was bouncing off the rev limiter with a 5500 rpm chip in it at the time, and the tach was reading right at 5000 - or very close. It was kinda hard to tell exactly because I'm still getting used to the beast and 5000 rpm arrives REALLY fast in this thing... 

Bear


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## TommyG67 (Dec 17, 2009)

Thanks for the feedback! Sounds like good news for me - I'll try the tach output on the HEI (which I rebuilt form a wrecking yard unit with advance kit & adjustable vacuum advance). I'll let y'all know how it turns out.

I believe that the MSD adapter is to fix the problem with tach readings where the MSD fires multiple times at less than 3000(?) RPM. Idle tach readings are WAY OFF, as the tach reads the multi-spark as higher RPM.


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## Pontiacdude (May 4, 2011)

I installed Electronic Ignition in my 68 GTO with the rally dash and indash tach. Hooked tach into the cap where it said tach. Tach worked fine.


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## Rukee (Feb 8, 2007)

BearGFR said:


> :agree I have an aftermarket Proform HEI in my 69, and it has two connections on the cap -- one for 12v in (ignition) and the other for the tach. I connected my in-dash Rallye tach directly to the tach lead on the HEI, through a fuse, and it works. I'm not convinced the caibration is accurate though - it seems fine at idle and low rpm, but up around 5-grand or so I think the tach may be reading low. The other evening I was bouncing off the rev limiter with a 5500 rpm chip in it at the time, and the tach was reading right at 5000 - or very close. It was kinda hard to tell exactly because I'm still getting used to the beast and 5000 rpm arrives REALLY fast in this thing...
> 
> Bear


Keep in mind, the motor revs up way faster then the tach can keep up!!


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## BearGFR (Aug 25, 2008)

Rukee said:


> Keep in mind, the motor revs up way faster then the tach can keep up!!


Yeah, then there was the converter issue I had too that wasn't helping matters. I think it's better now, but won't know for sure until I get some dry pavement. 

Bear


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## bullet20cc (Apr 4, 2009)

*Tach*

Most HEI systems are analog. MSD has some new digital units out. Most all tachs are analog if they have a swing needle and will work with most HEI systems. Digital tachs use lighted numbers to tell rpm. Then you may need the MSD tach adaptor.


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## TommyG67 (Dec 17, 2009)

Thanks to all who replied - finally got the engine fired and found 2 instrument issues (that are maybe related?). The Rally tach reads ~1/2 what I'd expect and the temp guage reads somewhat high. I am wondering if a poor ground might be the problem? Bought.installed all new wiring harness (for HEI & Rally tach setup), but perhaps the ground in the panel board is not as good as it should be? Any suggestions?


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## BearGFR (Aug 25, 2008)

If your car originally had lights instead of gauges did you swap out the printed circuit board on the rear of the cluster with the one for gauges? The ones for lights and the ones for gauges are different.

Bear


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## FlambeauHO (Nov 24, 2011)

My HEI 400 with rally tach reads about half what it should also. I figured it was just because its HEI. I know my grounds are good...


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