If you do much highway driving in 5th gear then the jump to 3.9 will be a little too aggressive IMO. If you track the car or do mostly city driving then it would be pretty fun.

 

damn. i know what ill be doing this winter.

i went with a modest setup when i did my torque converter. just knowing that i could of had it tweaked a little more for the same price makes me cringe. if your going to do it and pay for it anyway, i say go all out. im going to look into the 3.9

i wont be able to drive in drive mode with a 3.9

 

I just found this thread after replying to another about the AT5 gearing. There have been approx 6 people with the 3.7? Who are they and where is the feedback?

 

Well, i don't have any feedback but I have a complete 3.7FD VLSD setup sitting at Performance Nissan. My plan is to install into my 5AT G35 sedan but I'm also thinking of selling it given the right offer. PM me if interested or with questions. Thanks.

 

Yeah, so how's that coming along?


Jason, for my own personal reference and after reading your posts, I created a full chart of the gear ratios and speeds between the 5AT and 6MT. Honestly, I don't think its a huge deal on the 5AT vs the 6MT because the gearing isn't that radically different. The 6MT is a bit narrow in ratios, but overall, they are fairly close in the top 2 gears. The ratio for 4th gear on the 5AT is 1.000 and 5th gear is 0.834, for the 6MT, 5th is 1.000 and 6th is 0.794.

So at 6000 rpm, 5th gear on the 5AT would be about 145 mph vs 153 on the 6MT. With a 7200 rpm redline from a reflash, your top speed would hit about 170 on the 5AT and 180 on the 6MT. All things equal, the 6MT would have that slight edge in top speed, but it would have to shift sooner than the 5AT. So if 3.9 is suitable for a 6MT, I really don't see why its unsuitable for a 5AT. I'm willing to trade off the slightly higher RPM in 5th for wider gearing in 1st through 4th. Besides, with the same FD ratios, 4th on the 5AT is identical to 5th on the 6MT. So unless you can hit 165+ on a road course, I don't think the 5AT would ever be at a disadvantage.

I used the same formula you did with a small change. For tire revolutions per mile, I used 758.81 for my 275/35/19 tires.

Engine RPM / Gear Ratio / FD Ratio / Tire Revs per Mile * 60 = Speed

5AT Gearing - 275/35/19


6MT Gearing - 245/45/18