tachometer drive ratio?

[bevans6]

My engine has a tachometer drive coming off the blower in some way.  It probably has a gear ratio driving it at other than blower speed, in order to make it useful.  Does anyone know if Detroit had a standard ratio for the tach drive to crank speed?  I was just going through some stuff and found a cable drive tach that I might try to hook up.  Picture has it showing with a little blue cap on it, just beside the blower drive cover plate.

Thanks, Brian

[eagle19952]

I think the drive is specific to the tach...I could be wrong I often am...

[luvrbus]

That drive to the angle can be from 1.80 to 2.05:1 ratio are you your the tyne shaft is there most get broken off over the years and are never drilled out

good luck