Factory tach runs too high off calibration

[dammstrate]

So I got the factory tach on my 67 R/T to work, was a couple of loose/cut wires. But it runs off calibration, seems like about 30-35% to high. Not just a constant offset. 700 rpm idle measured by a timing light was ~1000 on the console tach. What I perceived as 3000rpm read about 4000, and running it up pegged the tach >6000 well before my spidey-sense said we were anywhere close to that, maybe 4500.

--> Any ideas to bring this in line?

 

[WileE]

Install a Sun Super Tach in front of the factory gauge.

 

[dammstrate]

Install a Sun Super Tach in front of the factory gauge.

Well that would kill the whole "stock" thing, wouldn't it....

 

[WileE]

Well that would kill the whole "stock" thing, wouldn't it....

Of course, if that's what you're looking for.

 

[Geoff 2]

So you are surprised a 55 yr old tach is reading off?
Get it calibrated. Also, some of the resistors & capacitors may have drifted off value over time & need replacing.

 

[Sinitro]

Have U updated the ignition system?

 

[hunt2elk]

Have you converted to electronic ignition without upgrading the internals of your original tach?

 

[Demonic]

The old tachs were notoriously inaccurate. I put a RTE tach board in mine and calibrated it myself. This is not for the technically unskilled.

RTE 67-74 Tach kit - rte

www.rt-eng.com

 

[AR67GTX]

It would help to know if the tach has the original board in it or an updated circuit board. Mine has a new board and has a calibration adjustment on it to tune it to match a reference tach.

As an aside I calibrated mine to read according to a tach I had mounted on the steering column while repairing/updating the factory tach. I then closed it back up and got the console back together, climbed into the seat and started the engine up - WTH - it’s reading too low. Then I bent down to stare at it at console level and realized it was reading the same but looking at it from above gives the needle a distorted point of reference on the scale. At the other end of the scale it will probably read high. Those console tachs are kind of cool but pretty worthless to drive by.

 

[Billccm]

The rt-eng.com tach boards play well with MSD and many other electronic ignition, and good ol'points too.
I like the tach boards that have the built in calibration circuits.
If you can solder the rt-eng.com conversion is easy. If you prefer they will also convert and calibrate your tach.

 

[Don Frelier]

Have you converted to electronic ignition without upgrading the internals of your original tach?

You can use a 66 tach with electronic ignition with no issues I did it for years.
Mine was always pretty accurate too.
It just takes the signal off the - coil which is essentially the same to the tach as with points.

 

[Sinitro]

Can't comment much about the 67 tach...
But in my 70RR the OE tach/clock was way off after I installed the Mopar electronic ignition system..

Just my $0.02...