LuigiVampa

I installed an Autometer shift light which has a digital tach readout in the center of the tach. It is pretty nice.

One problem - the digital tach consistently reads 300 RPMs less than the stock (dash) tach.

I double checked my wiring and settings and everything appears to be correct.

Anyone have any thoughts on the reason for this difference?

Thank you.

V2Rocket

stock tach might just be optimistic. try running to the rev limiter and see which says what. should be ~6520rpm.

FrenchToast

I think that's pretty typical. I've heard of similar situations, with about the same RPM difference. Maybe 200.

You can always call an AutoMeter rep and ask, they probably get that a lot.

Running it to the limiter isn't the best idea, especially on an unloaded engine.

I think its fine.

However, I'm not an expert, so either call a rep or wait for another response!

Take care!

LuigiVampa

Actually I was thinking this would fix my problem. When the engine blows both tachs will read ZERO and no more discrepancy.

I'm going to contact Autometer as well. Thanks.

Eric_Oz_S2

My S2 tacho also reads around 200-300 rpm higher than what the real rpm is as logged by my datalogger directly from the DME. I would say the error is with the stock tacho.

LuigiVampa

Thanks for the additional input. My tach is wired to the coil, not the DME, so I guess that rules out that variable as well.

FrenchToast

That should work. Is there a true zero mark on the stock tach though?

Given the other comments, I think the discrepancy is probably normal.

BTW, sending you a PM

Take care!

Dave W.

Agree. I see the same thing on my car.

Rogue_Ant

Yep - the stock tach is typically a bit optimistic. I've verified this across both internal DME logging, and external loggers.