Anyone have any info on upgrading our diffs to the 3.9 gear? Did a search on this forum and came up with nothing. Did some internet research and found that two companies sell the gear for G35 6MT's: 350evo and Central 20.
Apparently, there is a 10% difference with this shorter gear compared to stock, which would get your revs up quicker through each gear and for those revup motors with the higher redline, could be a good match to get more of that torque power quicker and still not have to upshift sooner. Anyone have any thoughts?

 

you will have to upshift sooner if the gears are shorter. You gain more power put down but give up some top speed in each gear so you will reach higher rpms faster and thus will have to upshift.

 

It's not the mechanical part that I'm worried about. It's the electrical part (ie... speed sensors, cruise control, etc.... ) that needs to be addressed

 

^^ But you have an auto... snicker snicker
j/k

 

I am going to order the 350EVO one later...

True you will lose a little top end speed in each gear but the acceleration and torque increase is well worth it in my opinion. You will have to upshift sooner but it won't be so much as where you will notice a huge difference.

 

you don't lose anything with the 3.9 as far as speed sensors or VDC or cruise control. I would know, I've had it for over a year and a half now

 

^^ that is in direct contradiction to every other post I have read about the 3.9 gear swap.

My understanding is that you do lose the cruise control and fuel economy suffers... But since I didn't swap (due to such reported issues), I defer to others to chime in.

Look for posts by ISMSOLUTIONS - his posts about issues from the swap were the first experience I read about - and he has a (12 sec) 5AT as well.

BTW, if you are a 5AT, it will give you a much larger performance boost as you are moving from 3.3 to 3.9 (vs. 3.5 to 3.9 for 6MT).

 

^^I heard the same as well, that you lose crusie control.

 

On most cars you'll loose cruise control, Speedo will be off, VDC and ABS might be slightly more sensitive because your ECU thinks your going at 45mph when you're really doing 40 and as you go the bigger the variation gets..

To fix this you'll need something that'll reflash the ecu.. you can try a friendly dealer for a cost