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Tachometer tech


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Hey all,

Currently I working on a project to build a replica of the stock Gemini tachometer. They were a pretty rare option so purchasing a cluster with one is getting really expensive.

It looks like this:


My plan is to pull a tachometer unit from another car a bolt it up to a new face that i'm working on. I've looked through pretty much every car at my local pick-a-part and have not found a replacement that has the indicies in the same locations as the Gemini ones. The ones I have found that are very close appear to be "air core" gauges, which, rather than having a postive, negative and signal wire, have sin+, sin-, cos+ and cos-. I assume that these are run from the car's ECU or some kind of microcontroller?

So I guess at this point I have two question:

1. Can I recalibrate another - regular type - 0-8000rpm tacho unit to line up with the indicies in the right place by modifying it somehow?

2. How do you get an air core tacho to work? Can I make my ECU (Link Xtreme G4X) do it with the right calibration? Or, can I somehow make it work with the oldschool coil signal?

The lazy way out is to just make the face to line up with whichever tacho unit I pull from the doner car, but I would really like to have the face looking at OEM as possible.

Anyone know about this stuff?

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9 hours ago, kws said:

You could use something like this, https://spiyda.com/smiths-rvi-rvc-conversion-external.html

Its the same guts, just in an external box, that im using in my tacho for the Marina. https://tasteslikepetrol.net/2021/06/project-marina-tacho-conversion/

Calibrate it via frequency audio files and then drive it with the coil.

Thanks, this looks interesting.

8 hours ago, kpr said:

if drive tach from your link ecu,  you can change the multiplier  in the software  so it reads correct.  

I will be driving it from my Link, but I was hoping to create something that might also work for people who are still running the stock dizzy or a different ECU.

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A follow on question, how accurate are tachos? Obviously your eyes can't actually see micro variations in rpm and translate that to a number, but how close is close?

I found this EK Civic tacho is is pretty darn close. I'd hazard a guess that if I used this unit it would not be that noticeable. I laid it over the Gemini one.


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