Converting "2000 PPM" based speed signal to PPR
 

The Holley HP can't understand the T56 speed sensor so I have to feed it a 2000 PPM (pulse per mile) signal from a Dakota Digital SGI-5c speed signal converter. It's basically the cruise control output of the device.

However, the Holley ECM is assuming that any signal it receives is a speed signal (Hz) from the trans ECM, and it calculates ground speed by knowing the pulses per revolution of the speed sensor, axle gear ratio, and tire diameter. I need to fool it by putting in the equivalent "Pulse Per Rev" at the trans sensor, for given a "2000 PPM" type signal. Anybody want to tackle that math?

Note that the speed sensor in the T56 trans is 17 pulse per rotation.

Re: Converting "2000 PPM" based speed signal to PPR
 

Gosh, I was over thinking this and making it harder than it was. Got more simplified with my approach and the answer revealed itself...

Given:

Speed signal @ 2000 pulse / mile
3.73 axle ratio
26" diameter tire

Solution:

A) Distance traveled per tire rotation
(26 inch)*(pi) = 81.68 inch

B) Tire rotations per mile
(63360 inch/mile) / (81.68 inch/rotation) = 775.70

C) Virtual speed sensor rotations per mile
775.70 * (3.73 gear ratio) = 2893.35

D) Virtual speed sensor, Pulses Per Rotation
(2000 pulse/mile) / (2893.35 rotations/mile) = 0.691

Only problem is the Holley HP software doesn't accept a value less than 1 so I will have to fake the gear ratio to compensate.