If I was planning to do a lot of long distance driving, would it be possible to change the gear ratios on my car? They are like this at the moment:

1st 3.540
2nd 2.264
3rd 1.471
4th 1.000
5th 0.834
6th -
Reverse 2.370

I know it doesn't look like it, but the difference between the 4th and 5th gears feels almost negligible when shifting. Would it be possible to make the 5th gear have a ratio of 0.7 or lower?

The car is a 2007 g35 coupe (automatic).
Thanks for any help.

P.S. I'm a woman so would it be possible for someone who doesn't have much mechanical prowess to do this?

 

From a pure economic point of view reducing top gear rpm by 16% would probably yield a 8% increase in steady cruise MPG. The same amount can be accomplished by just reducing the max cruise speed by 16% down to 55-60 mph from 70 mph.

Removing and redesigning the transmission internals would surely cost more than you could save in 6-10 years even 20 years* of ownership in MPG increases.

* assumming gas stays at $4 and doesn't go to $15 per gallon.

 

350evo makes a 3.9 final drive
Central 20 makes a 3.9 final drive
Nismo has a 4.083 final drive

You have an auto, you have a 3.3 final drive
Manuals have a 3.5 final drive
M35 sedans have a 3.7 final drive

Choose your destiny.

I don't know how you would change a certain specific gear ratio, but if you can, good luck!

 

you might be able to make some changes to your wheel and tire combination size to affect your fuel economy as well as perhaps changing the final drive ratio so that the net effect would be increased fuel economy.

specifically changing gear ratios seems like a rather expensive venture.

 

The whole 3.9 final drive setup costed me roughly $1400 for my auto.

 

those would all result in an increase in revs at a given speed, and be the opposite effect the OP would want.

 

Unfortunately the 5th gear 0.83 ratio has stayed the same since 2002 on 5AT........there was a ~2.9 diff gear in 2002 Q45 [only that year][ and a 3.133 in later years and early M45] that might provide the economy you desire with the loss in performance.

Unfortunately increasing tire rolling circumference is limited to maybe 4% [27/26 = 1.038] by rubbing/clearance problems.

The limiting problem is the low rpm lugging around town/up mild hulls with AC on............AT programming - speed vs load downshifts.

 

Why didn't you just swap out you 5AT pumpkin for the 6MT one? You can find these all over My350z, and you can usually find these with aftermarket LSD's already installed for cheaper than what you spent....

For 5AT guys, even boosted ones, usually the most cost effective is swapping the stock 5AT rear end for the 6MT ones.

p.s., I don't know what the OP wants, since it goes contrary to what pretty much everybody does.