Street Rat

Also can they be calibrated?
If so where can I have it done?

I'm talking factory tachometers.

mrvette

I proved my tach out with a oscilloscope and a digital signal generator ....

it was dead nutz on up to about 2500 rpm, after that it gained until around 4500 rpm it was about 10% over at 6k it was reading like 6700 +

I found the same with a GPS and the speedometer....dead on up to 70, at 80 indicated it was really 78mph.....at 100 indicated it was only 94mph....

I ran outta room, test over......

jb78L-82

My factory tach is 300 rpm high @ 60 mph and 400 rpm high by 4,000 rpm..Indicated 6000 rpm is about 5,700 rpm'...Mine is definitely off and reads higher than actual rpms

zwede

Same here. Factory tach (I use a 75-77 tach in my '71) was spot on to about 3,000 or so and then started reading high. I think it was about 300 rpm high at 6,000.

When the factory tach board failed I got a replacement from Wilcox and I think it had an adjustment pot on it. I do remember I was able to get it spot on all the way past 6,000.

Street Rat

The main reason that I ask is this.

I recently installed a rev limiter with a 5800 rpm chip. I was testing it out and it didn't hit until about 6200 rpm on the factory tach.

I was simply curious if it was the tach reading incorrectly.


Tach board has been replaced.

jb78L-82

That difference is almost spot on to my 78 factory tach.....6,000 RPM incidated is about 5,700 rpm' actual

Street Rat

From everyones responses, it seems that the factory electric tachometers are not very accurate.

Eventually I plan to replace all gauges including the tach with some Autometer gauges.

Thanks for all of the responses.

gkull

The plug in chip rev limiters can also be off by 100s of rpm's. Years ago I put my vette up with a snap on timing light hooked up and set to rpm read out and my msd 6 was way out no matter what chip I installed. I replaced it with the crane digital and I matched the settings

zwede

Probably designed that way on purpose to reduce warranty claims is my guess.