I understand that the gap between the gears is unchanged. The gap in the power to the ground, in absolute numbers, is. Proportionally, it's the same.

I think you misunderstood my point.

 

who cares about thes technical mumbo jumbo? It makes the z faster...period. Only time i would think twice is if i was going to go turbo with big horsepower.

 

Has anyone actually proven this with a timeslip though? The acceleration through each gear is quicker, but there is more shifting going on and/or the gearing may cause the engine to run through the powerband too quickly in 1st and 2nd. If adding gears was the answer, then why stop at a 3.9? Why not a 5.0? It is very possible to overgear a car. With the VQ35s fat and wide powerband, it's not remotely as dependant on gearing as something like a 3.0 VTEC V6.

 

I think that's why Nismo only went with 3.917 instead of say a 4.1...
Any tighter, and you'd have to rebuild the motor to get the RPM's up. The higher you can rev, the tighter your gearing can be, without loss of top end speed.

 

Let me rephrase......its faster through turns, so maybe not for a dragstrip.

 

it definetly helps your top end accelleration. You really feel the difference in 6th gear when cruising on the highway. It's no longer a lazy gear

 

+1

Overall I think the 3.9 gears are one of the best bang for the buck mods out there for the 350Z. I really could care less about 1/4 mile times. I got the gears for overall performance. I have had mine for a year now and love them.

 

I've only had the car back for about a month since getting everything worked out so I haven't had a chance to go to the track yet. I'm hoping to get back to the track before the end of the month so I can do some runs and make some comparisons.

 

The 3.9FD will help acceleration through all the gears. It doenst matter if u are on a drag strip or on a track.

 

There is no cheaper option for a 3.9 FD than going for the Nismo 3.917 for +-1300$?

 

I remember originally reading a year or two ago when the 3.9 gears first came out they were supposed to reduce your 1/4 mile time by like .5 seconds and your 0-60 by like .2 seconds. However, someone later came along and squashed it because he did before/after comparo's and it made little difference because of the extra shifting.

I think its mostly designed for road-racing and auto-xing, for more responsive power bands and such.

 

I suppose that matters if you only drive your car at the drag strip or if you have a magazine journalist reviewing your car's 0-60

otherwise everything else is faster. If you're going to drive up to 165 mph, you have to shift 5 times no matter what. Your rpms are still going to be higher in each gear which puts you higher in the torque/hp band in addition to the 10.6% gearing multiplication punch

 

unless you have this mod and have tested it why do u think your so smart? people have shown there 1/4 times werent any faster, thats what were discussing genius.

 

Sure there is:


http://z1auto.com/prodmore.asp?model...ne&prodid=1726

16 sets coming end of the month, still have a few sets left

 

Just ordered the 3.91 gears, great price. Thx for the info

 

Final Gear RPM formula: FYI

Tire diameter will also have an effect on a vehicle's final drive ratio. As tire diameter changes, so will engine rpm at a given speed. This can be demonstrated this with the simplified formula: rpm = (mph x final gear ratio x 336*) / tire diameter (*the constants of time, pi and distance have been simplified and replaced with 336). For example, given 65 mph, a tire diameter of 30 inches, and a final gear ratio of 4.10, the engine speed will be approximately 2,984 rpm--(65 mph x 4.10 final gear ratio x 336) / 30-inch diameter tire. If we reduce the tire diameter to 25 inches, the engine speed increases to 3,581 rpm. By installing shorter tires, the vehicle will accelerate as though it has a 4.73 (higher numerically) gear without the expense of gear swapping.

 

This assumes a high gear ratio of 1 times the axle's gear ratio

Tire size: 245/40/17 (stock Z)
65mph*3.53 rear end ratio*336 / 24.7 tire diam (17") = 3121 RPM

Tire size: 275/35/20 (mod Z)
65 mph*3.53 rear end ratio*336 / 27.6 tire diam (20") = 2793 RPM

Tire size: 245/40/17 (stock Z tires)
65 mph*3.91 rear end ratio*336 / 24.7 tire diam (17") = 3457 RPM

Tire size: 275/35/20 (mod Z)
65 mph*3.91 rear end ratio*336 / 27.6 tire diam (20") = 3094 RPM

 

you guys need this site - it's a sticky in this forum

http://www.f-body.org/gears/