I'd like to replace the gears in my '05 sedan to the 3.90 gear ratio...

Does the Infiniti Dealership have a way to change the speedo reading after install?

James

 

Nobody talks about gear ratios on this board, probably because Infiniti doesn't really advertise what the final drive ratio is or at least I haven't come across it in any post or in the brochure. I think a 250 hp car with 3.90 final drive would feel much more responsive under 60 than a 300 hp car with a 3.07 or something like that.

 

I thought speedos were run off of actual tire rotations?

 

I think the spedometer is driven by the VSS (Vehicle Speed Sensor) which is mounted to the transmission. I believe all of your wheel sensors are for ABS and VDC. The VSS should be a relatively simple magnetic pick-up which will produce a pulsed output that is proportional to vehicle speed. I don't know if you or the dealer can get into the computer and change the calibration of it. You might have to do something like make an electronic interface module that multiplies the VSS signal by some constant which you would have to figure out. I might be way off on all of this but it is my own personal theory. By the way, where are you getting the new gears at for the rear end?

 

Talked to two 350Z owners who have done the 3.9 gear change and heavily considered it myself. Your speedo is not affected. Speed is read from the rear wheels, not the tranny. At any rate, if you have an auto, then the 3.5 gear from a six-speed might be a better option for you.

 

How much of a difference do you think this would make? in the low end I assume? and how much would it cost? I have the 2005 6 speed.

 

i heard it got some 350zs in low 13s just with gear change... dunno rumors spread around