diesel tachometer

[pologuy14]

i recently got a new alternator w/ the pulse terminal for a tach signal. i have a diesel auto meter tach that reads 0-4000.i have a dakota digital box & i kno i can change the reading but im not sure what to change it too i would like to make it more accurate then it is.. it reads aprox 650 @ idle & 3800rpm @ 65mp (33" tires 4.11 gears, 3rd gear [th400 1:1]). according to 4lo.com (http://www.4lo.com/calc/gearratio.htm#ratios) it should b 2720 rpms... i kno for a gasser you can use a timing light but how do i check rpms for a diesel?

[JohnC]

Got a laptop? Download this program (http://www.tunelab-world.com/rpmsound.html).

[pologuy14]

i'll give it a shot

[convert2diesel]

If you don't have a computer or hand held, the old school way is to use white paint on the front damper. Oh yah, you'll also need an old incandesant light and a dark garage.

Electricity on this continent is delivered at 60 cycles/sec. That translates into 3,600 cycles/minute. That also means your light bulb also cycles 60 times a second. If you were to paint a single white line on the damper and raise the RPMs, when the line appears stationary, then the engine is doing exactly 3,600 RPMs. As our engines are governed for that I choose to use 2 lines, 180 degrees apart. When the lines appear stationary the engine is turning exactly 1,800, four lines, 90 degrees apart equals 900 RPMs.

The nice part about this is it's exact to within 3 to 5 RPM (power is not always delivered at exactly 60 cycles but should to be within 2 %). Not as cool as using a computer but it does work with the same accuracy.

Bill