l have a 2004 Infinity g35 automatic. (wish l could of found a manual) Does any one know if you can change the rear gears to increase the bottom end.l use to have a 91 Mustang gt 5.0 and by changing my gears from a 2.73 to 3.73 it made a huge difference at the light.

yes they make different ratio is for those cars, they are very hard to come by. i've only seen one posi trac diff, and that was the first one in the states.

l havent heard of anyone doing it on the infiniti but get more air flow. headers will help too.

For the cost in getting a new rear end and changing the gears, you can probably just install a supercharger and upgrade your torque converter.

Keep in mind, the 'dime a dozen' mustang used cheap parts that are easily and cheaply replaced. Not so easy on a G car. You're better off upgrading to increase air and fuel flow. Oh yeah, changing your gearing might also screw with your auto tranny or traction control and the many many sensors. You're in for a big headache.