RPM TACH accurate or not

[ROCKRTX]

Did somebody ever test the accuracy of the apex RPM tach?

I add a washer on my clutch kit to bring at 10800 RPM and loose 1-2 MPH since.

Just wonder if i am really turning at 10800 or if my Tach read a little high.

 

[Triple X]

I did the same thing, it was reving a 11,000 so I put 1-2 gram washer in to bring down rpm's to around 10,7-10,8. It was slower, took them out rev's 11,000 agian and top end came back, they must be out alittle.

 

[kviper]

I have heard 2 to 3 hundred RPM variance. kviper

 

[SledFreak]

If the tach read 11,250, but it was actually 10,900, but the ECU thinks it's 11,250, then would that kick the rev-limiter... If the ecu reads the tach RPM, then the sled is not running the way they should, correct? If this is true, then I wish I would have known that a whole ago.. How can we tell if the tach is accurate to the atual engine RPM?

 

[tttario]

If the tach read 11,250, but it was actually 10,900, but the ECU thinks it's 11,250, then would that kick the rev-limiter... If the ecu reads the tach RPM, then the sled is not running the way they should, correct? If this is true, then I wish I would have known that a whole ago.. How can we tell if the tach is accurate to the atual engine RPM?

You could use a digital "pen style" portable tach and place it on the primary bolt. Then multiply by the gear reduction and that will get you very close. Then compare actual to display.

 

[LazyBastard]

If the tach read 11,250, but it was actually 10,900, but the ECU thinks it's 11,250, then would that kick the rev-limiter... If the ecu reads the tach RPM, then the sled is not running the way they should, correct? If this is true, then I wish I would have known that a whole ago.. How can we tell if the tach is accurate to the atual engine RPM?

The ECU knows the real engine speed. In fact, the ECU knows exactly at what angle the crank is at all the time. The inaccuracies in the gauge come from the fact that it is a balancing act between a spring and a magnet.

 

[SledFreak]

But, it's hard to be accurate on the clutching if your tach is off by that much. Allen Ulmer told me he has seen them as high as 500RPM off. That's not the norm, but I'm hearing 2-300 is pretty norm..

 

[SledFreak]

Just went for a ride and checked my LCD display off my PCIII and it was out by only 100RPM..

 

[ROCKRTX]

lower of 100 rpm is 1-2 MPH less on top

 

[LazyBastard]

Good thing these things aren't 2-strokes....