Mechanical speedo
Thread Starter
Launching!
Joined: Oct 2004
Posts: 238
Likes: 1
Mechanical speedo Need a math whiz!
My '98 LS1 / T56 is finally resting in my 89 RX7. I want to use a stepper motor to drive the RX7 mechanical speedometer cable using the PCM VSS out signal to drive the stepper. The stepper needs four pulses per revolution. The RX7 tranny output shaft turned the speedo cable once in 3.5 revolutions of the output shaft. So I need get 3.5*4=14 pulses to per output shaft rev to drive the stepper. As I understand it the PCM uses the rear end ratio to adjusts the VSS input from the T56 to drive the Chevy electrical speedo.
What value of rear end ratio should I set in the PCM to give me the 14 pulses per rev?
Is that clear as mud?
My '98 LS1 / T56 is finally resting in my 89 RX7. I want to use a stepper motor to drive the RX7 mechanical speedometer cable using the PCM VSS out signal to drive the stepper. The stepper needs four pulses per revolution. The RX7 tranny output shaft turned the speedo cable once in 3.5 revolutions of the output shaft. So I need get 3.5*4=14 pulses to per output shaft rev to drive the stepper. As I understand it the PCM uses the rear end ratio to adjusts the VSS input from the T56 to drive the Chevy electrical speedo.
What value of rear end ratio should I set in the PCM to give me the 14 pulses per rev?
Is that clear as mud?
Originally Posted by RFERG43
Need a math whiz!
My '98 LS1 / T56 is finally resting in my 89 RX7. I want to use a stepper motor to drive the RX7 mechanical speedometer cable using the PCM VSS out signal to drive the stepper. The stepper needs four pulses per revolution. The RX7 tranny output shaft turned the speedo cable once in 3.5 revolutions of the output shaft. So I need get 3.5*4=14 pulses to per output shaft rev to drive the stepper. As I understand it the PCM uses the rear end ratio to adjusts the VSS input from the T56 to drive the Chevy electrical speedo.
What value of rear end ratio should I set in the PCM to give me the 14 pulses per rev?
Is that clear as mud?
My '98 LS1 / T56 is finally resting in my 89 RX7. I want to use a stepper motor to drive the RX7 mechanical speedometer cable using the PCM VSS out signal to drive the stepper. The stepper needs four pulses per revolution. The RX7 tranny output shaft turned the speedo cable once in 3.5 revolutions of the output shaft. So I need get 3.5*4=14 pulses to per output shaft rev to drive the stepper. As I understand it the PCM uses the rear end ratio to adjusts the VSS input from the T56 to drive the Chevy electrical speedo.
What value of rear end ratio should I set in the PCM to give me the 14 pulses per rev?
Is that clear as mud?
keep in mind that if you lie to the PCM about the final drive ratio, internally it will believe the car is going a diffrent speed then it is. so you would have to skew all of your MPH based numbers
the VSS output is 4000 pulses per mile... constant. i would work on converting THAT signal to what your stepper motor needs thru another black box... not mess with the PCMs speed calculation.
4000 PPM = 66.666666666666666666666666666667 pulses per second @ 60mph
what you really need to figure is the number of speedo cable revs at 60mph, and work backwards from there.
what you really need to figure is the number of speedo cable revs at 60mph, and work backwards from there.
