Factory Tach Accuracy

[JD1964]

I now have a Raptor shift light and its working great. However, it's settings dont agree with my factory tach. There is a 300 rpm difference roughly. To shift where my tach says 5900, I have to set the Raptor to 5600.

What do you think is happening here?

 

[jrichker]

That sounds about right. I did a calibration check on a spare 89 Mustang factory tach I had and the high RPM range was about 300 RPM off. The tach can be made to read dead on for a very narrow range of RPM, but it will probably be off by 300 RPM somewhere else in the range.

The 92-93 tachs supposedly have a better calibration setup, but I have an older tach and can't verify that statement.

 

[A5literMan]

I was just going to say 200-500rpm off compared to an aftermarket tach has been normal for me on 2 cars that I switched over.

 

[JD1964]

So, you guys are saying I should trust the Raptor setting and assume that my factory tach reads 300 rpm high at the top end?

 

[A5literMan]

Yes.
Besides its safer lol. Keeps you from over revving. If you take it to the track you can always see where the car likes to be shifted and adjust accordingly

 

[HemiRick]

Yes the factory tach in my 89 goes to 7000 and doesn't even kick in the ECU rev limiter. The factory tach reads way over IMHO.

 

[96pushrod]

Yes the factory tach in my 89 goes to 7000 and doesn't even kick in the ECU rev limiter. The factory tach reads way over IMHO.

I agree. We have seen factory tachs read 6500 and only seen 5500 on tuner studios. They’re quite a bit off sometimes.

 

[Mstng93SSP]

And who knows how much that tach is off now 5 years later..