Has anyone measured their 0-60 or 1/4m times with the 3.9 final drive change? I'm thinking of doing this but need to know approx how much faster your times get...

EDIT: err i meant 3.9

 

It helps but I don't know if it would help your 1/4 much. It would help for more city style driving.

 

i saw someone saying it brings the 1/4 mile down by at least 0.5 seconds... some other guy with a 350Z was apparently getting sub 5 0-60 times so i wanna see if this is really true...

 

Taller gears will help you launch quicker, but you loose some top end.

 

Not to mention your highway mileage would drop a few mpg. And we don't have much to spare!

 

This is pretty much wrong on all counts. 3.90's are shorter gears than stock, not taller - the larger the number, the "shorter" the gear. Your car will stronger in every gear, not just at the launch - but this is limited by the ability of your tires to maintain traction.

You will lose top speed from your rev limited maximum, but that's not a factor in the 0-60 and 1/4 mile scenarios you're asking about.

You also have to consider that you may need to shift one more time in a 0-60 or 1/4 mile pass which may (or may not) help your ET, depending on the shift point relative to the end of the run.

 

wow

 

I upgraded to the 3.5FD from my 3.3, and it is one of my favorite mods- the 3.9 seems a bit much for an automatic at least. It does however make driving pleasure a bit nicer since you're closer to the power zone in each gear, and you get ~8% more torque throughout the rev range...

I'm putting gears on my next car for sure.

 

I agree with Usual Suspect.
The 3.9:1 gears will help with quicker launches, provided you have the traction. If you are racing your car at a 1/8th or 1/4 mile strip this mod should definietly help, if this is the type of performance you are after.

 

Excellent points. A shorter gear will definitely help your 0-60 and 1/4 mile times. That's why people change to a shorter gear when drag racing. The downside is increased noise from higher revs, greater gasoline consumption while driving 70 mph or faster and top speed will be lessened.

Frankly, most people doing most of their driving around town would benefit from the gear change because you are in your torque curve more often. Your motor doesn't have to work as hard to get up to speed.

 

+1

There's often a lot of misconceptions on this.

 

Precisely.

 

Not necessarily on 1/4th mile, on many 13~14s cars, they can be touching the rev-limiter when they cross the line, but when you change out to a 3.9, you would probably have to shift to 4th; which would probably hurt your ET

 

Good point. Any extra shifting can hurt an ET. I have no idea what a 5AT would be doing for revs at the finish line with a 3.9.

 

That's not necessarily true. Deeper gears do not necessarily mean quicker ETs. If that was the case, then big block drag cars wouldn't be using 2-speed Powerglides and running 6s. Choosing the right gear depends on a lot of factors including:

1) Powerband
2) Tire height
3) Transmission gearing
4) Engine torque

It is quite possible to overgear a car and a 3.9 gear would do just that. Basically what will happen is the G35 will go too quickly through 1st and 2nd to give adequate acceleration. As for the 3.5 gear, I've tried it. I didn't have 3.5 gear in the diff, but I was running 23.5" drag radials which took my gearing from the stock 3.31 to a 3.55. On the same day, same track, the car WAS SLOWER with the 3.55 ratio. On average, it was .1 seconds and 2mph slower which was thanks in part to the early shift into 4th a few hundred feet short of the finish line. When the car his 4th, it just layed over. With the 26.2" stock height 17s, I am able to hold 3rd right until the finish or approximately 101mph.