I've got the 3.31 rear end in my car with the M47.
I just installed this rather expensive 52mm tach tonight and I don't believe it's working correctly. The needle moves, idle is indicated as about 650 rpm? (it's rather small, so I'm just estimating.) The dummy shift-up light comes on at abou 1500rpm according to the tach.
60mph = 2,000 RPM 80mph = 2800 RPM
I don't buy it... Redlining this tach would kill my engine ;)
Or maybe it's right and I'm just not thinking clearly?
This is mine:

I notice that the needle is different than the other ones I had in the past:

|