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Originally posted by 92BLKL98 How do I figure VSS Ratio in the ECM Constants table in CATS Tuner? Can this be used to calibrate the speedo for rearend gear changes?
on a 3rdgen, the VSS is a set number of pulses per mile.
to calibrate for rear end changes, you swap plastic gears in the trans.. just like cable driven speedos.
92BLKL98, the preferred way is what MrDude_1 said, you can also go with what Cliff92Z said, both will work.
i don't know about CATS, but with TunerPro RT with a 730 ECM running the AUJP bin with either 8d_v03 or Super_8dm2 ECU files, i know there you can make changes to alter the speed reading in the ECM.
the 8d_v03 ECU file is easier to set it with because it uses
0 - 255 for the setting where Super_8dm2 uses pulses per mile & when you change the pulse per mile enough the accept the
change, it changes by 1 number in 8d_v03.
as to how to calculate how much & which way to change it, i have no ideal, that would involve math & for me it was easier to run it on the dyno using real time emulation & my lap top.
