I'm on the fence about buying a G37 and was wondering if anyone makes a lower (<3.7) final drive for the manual transmission. I know most people want a more aggressive final drive for drag racing but I would be buying this car for a highway commuter and I want lower cruising RPM in 6th.

Is it possible to swap the automatic differential into a manual transmission car?

 

Search for "final drive ratio" and you'll get several threads on the 4.08 rear end gear and on how it's been done. Welcome to the forum.

 

Like how low in 6th gear? I usually hover around 3k RPM's going 75 mph. A regular 4 banger does about 2500 RPM's at the same speed (at least my wife's Toyota Corolla does).. 500 RPM's isn't much difference.

 

Vette's cruise about 1500 in 6th at 70mph. But they've got the torque to do it with a 400ci 435hp v8. We don't have the torque to cruise real low and you would be bogging the engine down and hurting mileage more than helping it.

 

BB he's looking to go the opposite way. EX. 3.50

...as others have said I think the car is geared relatively well. If your doing a lot of highway driving this vehicle for what it is will give you fairly decent MPG. Being to low is going to give a negative effect on the engine/load. For the minimal change vs. cost I don't think it's worth your time or money. If you really don't like it, look at a different vehicle. IMHO.

 

OIC. A lower final drive ratio is one that uses a higher numerical gear (like the 4.08 I mentioned). So the OP actually wants a higher final drive. I should have read the rest of the post more completely.

I don't see any reason why it couldn't be done that way. It doesn't matter if the final gear is from an AT or MT equipped car, it's irrelevant.

 

I was hoping something around 2k at 75mph in 6th. If I want to go fast I can use the other 5 gears.

 

Just so you're aware, swapping out the final drive gear will weaken acceleration in all 6 gears, not just 6th. And reverse too for that matter. But it should improve your highway mileage some. I'm pretty sure you'll be the first one here to mod the G37 to go slower so there's no info from a previous swap to learn from.

Do some research on the final drive gear ratios from other years of 350Z or G35, they should fit.

 

From what I read, The 7 spd autos come with a 3.357 differential, while the manuals have a 3.692 differential. I guess you can technically just get one from an automatic car. The flange on the differential that the driveshaft bolts to is different, but my understanding is that you can swap out the flange from your original differential. I don't know this for a fact. Others please feel free to chime in and correct me if I'm wrong. I have a 7sp auto and I was thinking about doing the opposite and swapping in a 3.692 differential with posi for better acceleration without spending extra money and time installing a 4.08 gear. That way my gas mileage wont be affected as much either considering I drive about 100miles daily.

 

I've looked at the FSM for the 6MT, 5AT and 7AT transmissions on the G and Z series (V36 and Z34 only).

From what I can tell:

The 5AT and 6MT Z/G, whether RWD or AWD, come with a 3.692 FD.
The 7AT Z/G, whether RWD or AWD, come with a 3.357 FD.

The difference:

The AT cars come with a 3-bolt flange for the driveshaft, the MT comes with a 4-bolt flange. The half shaft flanges appear identical, so is the diff case, and everything else.

Cars equipped with VLSD also appear to be identical in everything except for the number of pinion gears inside the diff itself. The VLSD comes with 4 pinion gears, the open diffs come with 2 pinion gears.

 

I assume you want lower rpms in final gear, to get better gas mileage. How many miles do you intend to put on the G, to break even for the expense of getting lower rpms at highway speed? Doesn't sound logical to me.

 

i have 4.083 ring and pinion. it might be easier to find an entire pumpkin to swap. i can tell you for sure, that the pumpkins are interchangeable between the 350Z and G35's and our cars.