Anyone know how many Pulses per Output shaft rotation?

[ewave]

Hi,

I'm trying to hook some instrumentation up to my Viper's speedometer input/transmission speed sensor output. I am trying to figure out how many pulses there are per output shaft rotation of the transmission. This must be an integer. Anyone know?

Thanks!

 

[DChan415]

There are 4

 

[ewave]

Hmm.. Weird... The number that I got from my math based on data measurements, was 23 pulses per 7 revolutions.. Or 3.285 for each one revolution. Big difference from 4 per revolution.

Which just couldn't be possible... Maybe my car isn't running the stock 3.07 rear axle ratio?

BTW the formula I am using is: MPH= (1/rear axle ratio)*(1/gear ratio)*(1/time between pusles)*(1/number of pulses per revolution)*pi*(RIM+(2*(335*0.35))/25.4)*(1/12)*(1/5280)*3600

Tires and rims on my car are 335:35R17.

There are 25.4mm in a inch, 12 inches in a foot, 5280 feet in a mile, 3600 seconds in an hour. Tire circumference in feet = pi*(17+(2*(335*0.35)/25.4))/12

In forth gear, gear ratio is 1:1
Rear axle ratio was 3.07:1
Rim is 17 inches
At 2000 engine RPM, my car was going 48 mph.

At 2000 rpm in fourth gear, the time between pulses would be 0.0075 seconds, if there were 4 pulses per revolution. With a 3.07 rear axle, then MPH would be 50.8

As I said, from the MEASURED time between pulses I have to use 3.285 pulses per revolution.

 

[DChan415]

huh?

 

[Johann]

I installed an aftermarket cruise control in one of my Dodge trucks and the instruction manual stated that most Dodge speed sensors with white/orange output wires put out 8000 pulses per mile.
With a known tire circumference and axle ratio, one should be able to extrapolate the output shaft turns.