Tach connected to alternator.

[BSMiller]

Connected an Isspro programmable tach to the alternator using 16 pulses per revolution. Actual calculation was just under 16 pulses. At idle tach indicated 700 rpm and at 65mph was 2000 rpm.

Would like to know if anyone has compared readings with a strobe?

 

[bgilbert]

My 5 speed and 3. 55 gears I see about 1800. Sounds about right, as I don't have mine calibrated.

 

[BSMiller]

I should have stated my 1990 Cummins is a D350 with a 727 transmission and 307 rear end. Would assume with a 5 speed in 5th gear the rpm would be at least 10% lower even with a 355.

Bruce

 

[JLEONARD]

I calibrated mine with a hand held tach. I was getting about 2000 rpm at about 70 mph. 5 speed and 3. 54 axle.

Close enough.

Jay

 

[bgilbert]

I calibrated mine with a hand held tach. I was getting about 2000 rpm at about 70 mph. 5 speed and 3. 54 axle.

Close enough.

Jay

Thats what I see at 70mph as well. Pic under BGilbert's truck in readers rigs.



With a 1:1 non overdrive transmission, you sound about right, 65mph 2000rpm.