maxpower_454

iTrader: (7)

I just bought a 02 WS6 M6 that supposedly has the stock 3.42 gears in it but the speedometer is inaccurate. What would cause this? I compared the speedo with my GPS and am running roughly 1600rpm at roughly 55mph. An RPM calculator tell me the gears are probably 3.42 so it must be my speedometer. How can I make it accurate again? How is it changed with a gear change? I'm thinking about 4.10's. I know it will make the rear weaker but I think the better driveability will make it worth it.

Duffster

iTrader: (103)

by inacurrate, how much? when the speedo says 55, what does the gps say? You gave a bit of the info talking about comparing the speedo & GPS at 1600/55mph but didn't describe what the inaccuracy was.

As to the switching gears, the M6 is FUN to drive and row through, but its not the ideal choice for higher gears like 4.10. You'll still cruise nicely at 65-70 (low engine rpm still) but you'll lose a bit of economy. I switched to 4.30 and while it's fun and feels like it accelerates faster, I would have gladly switched back to stock gears.

maxpower_454

iTrader: (7)

Oh, sorry, The speedo says about 42mph when the GPS says 55mph. I'm not saying the GPS is 100% correct but that's a pretty big difference. I will drive it some more and get more points to compare.

I'm not sure about gears and mentioning that may have made the post comfusing. I really just want to know how I can calibrate my speedometer to make it accurate.

Duffster

iTrader: (103)

the cheapest and easiest way to verify your rear ratio is to jack up the rear end, crawl under it, put a mark on the drive shaft and while in neutral, rotate the rear wheels and count the revolutions of the shaft. You could also remove the cover and count the teeth (this is the messy method). As far as calibration, you'll need the actual rear ratio and can get a programer like HPTuners or EFI Live and with the rear ratio, update the computer. That SHOULD get it done.