VSS and Gear Ratio?
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Joined: Jun 2002
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From: NH
VSS and Gear Ratio? It is early, but off the top of my head...why all the fuss about changing gear ratios using LS1 Edit or Hypertech, etc when the vehicle has a VSS and knows how fast the car is going. Does the PCM not tell the speedo or something? I have an autometer speedo which I will need to calibrate, but it has nothing to do with gear ratios. If I change the ratio, then I would just recalibrate. What else am I missing here?
Joined: Nov 2001
Posts: 1,707
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From: Anderson, Indiana
Re: VSS and Gear Ratio? Since the VSS is located at the back of the transmission, it has no way of knowing what you have changed AFTER it (gears, tire size). If you are using a 4L60E or 4L80E, this information is very important since upshifts and downshifts are based mainly on MPH! Also, if using a factory type of speedo, the only way to calibrate it is with some type of programming.
For sure, if you are using a manual trans or aftermarket speedo, it becomes far less important that the PCM sees an accurate speed signal, but you still have to watch for a big mismatch in some cases. If your MPH limiter is set to 160 MPH in the PCM, but you have changed gears, tires, etc., and your way off on your scale, the PCM may "see" 160mph when you're only going 65mph actual, and shut your fuel off.
The PCM needs to see some kind of VSS signal, even if terribly inaccurate, for other functions that it is used for.
For sure, if you are using a manual trans or aftermarket speedo, it becomes far less important that the PCM sees an accurate speed signal, but you still have to watch for a big mismatch in some cases. If your MPH limiter is set to 160 MPH in the PCM, but you have changed gears, tires, etc., and your way off on your scale, the PCM may "see" 160mph when you're only going 65mph actual, and shut your fuel off.
The PCM needs to see some kind of VSS signal, even if terribly inaccurate, for other functions that it is used for.
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91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
Thread Starter
TECH Apprentice
Joined: Jun 2002
Posts: 319
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From: NH
Re: VSS and Gear Ratio? I told you it was early. I also thought about it later. Makes more sense after coffee. Incidently, I do have a 6 speed. Currently running 4:56 rears and hope to get running before buying LS1 edit or other programmer. Thanks again.
Joined: Nov 2001
Posts: 1,707
Likes: 33
From: Anderson, Indiana
Re: VSS and Gear Ratio? Usually 160 mph. But some had non-Z rated tires (the ones with the steel driveshaft), and I guess those were 118 or 124 mph.
John
John
__________________
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
