Does anyone ever remember reading that the factory tach. on our cars is off by 1000 RPM's???

Please let me know where you read this at, I can't find it again..

I remember he hooked it up to a computer and said it was off in the high end of the gauge.. Can anyone back this up with proof???

 

that would be a lot to be off by.

 

My speedometer reads about .5 to 1 MPH slow at highway speeds. I can't imagine the tach being that far off. Did you read that the tach was reading low or high? IE, are you saying the actual redline is 5,500 or 7,500?

 

The tach isn't off at all. Rev-limit on an FS-DE is 7050 RPM. It's 7800 RPM on the FS-ZE. The DE can be safely run at 7800 for a short while, (then I assume it returns itself to basic element state) but why would you want it to? The power curve drops off at 6275 RPM anyway. With the limits set at these RPMs, try bouncing off it and look at the tach. Looks spot on to me.

Back to the original question, the tach should be spot on. Or at least only off by 100 RPM at the most.

 

I can imagine a speedometer being off by a couple MPH, because it would be sensitive to things like tire diameter (including wear and inflation) and so forth. But I think the tach measures RPMs directly off of the engine somewhere -- either the crank shaft or a cam shaft or what-have-you.

I have heard that factory tachs can be laggy -- your current RPM may be a bit different from the reported RPM. That's why people install aftermarket ones.

RPMs are reported as part of the OBD-II data stream, so an appropriate OBD scanner should provide something to check the dashboard tach against. Perhaps this is the type of "computer" referred to above.

 

Kind of off topic, but the tach on my 323 is spot-on. It's a cluster from an LX pro, but I got mad this weekend and ran it up to fuel cutoff in 1st gear which is I believe around 6300 for the SOHC B6, and sure enough, right on 6300 it cut out.

 

Maybe you guys should ask redrims and see if it is correct, he looks like he has had his car on the dyno... dont know if he could help with this question