Justin@IOS

iTrader: (3)

Well guys, I finally gave in and threw a 3.91 equipped diff in my car.
I was trying to wait until a new helical limited slip hit the market later this year, but I had a full rear diff w/ vlsd dropped in my lap, so I swapped in the 3.91 gears into that setup and bolted it up.

My observations on the vlsd:

The limited slip was LONG overdue. If I wasn't trying to hold out for the helical unit (and I'm still going to upgrade as soon as it's available), I'd have done this a LONG time ago. The older carrier swapped right in my 07 without any issues. If someone else has already reported this and I missed it, I'm sorry for the repost.

My observations on the gears:

First gear revs out very quickly now. I've hit the rev limiter a few times over the last few days because of it. Acceleration doesn't feel that much different and I'm not sure if it's due to tire spin, or if my butt dyno is just off. Second gear feels a little quicker acceleration wise and it's a bit shorter. I can still get to 60+ in 2nd gear (if you care about 0-60 times). Third gear is where the change is immediately noticeable. The car pulls MUCH harder in third now. Fourth through Sixth are also much quicker and the change is very noticeable. The car pulls easier through the gears and I can even cruise below 2k rpms in 6th gear and it'll pull out without bogging down.

Highway cruising at 80mph went up approx 300rpms, so it's not bad at all.

Overall, I'm very happy with the results. I'll get some numbers up in the next week or so, once I'm able to hit the track.

VitViper

iTrader: (1)

I have the 4.08 and it just owns face. And the top end is definitely still there. Had a little "spirited driving" against a buddy with a 2000 bmw 540 (282hp 4.4L v8) and even with all the extra crap in my car I wipe his car across the road like nothing. Probably 3-4 football fields on him by an undisclosed top speed >.>

Justin@IOS

iTrader: (3)

I did some more testing last night and my butt dyno was off a bit in the lower gears. Even though I'll occasionally get some tire spin at the top of first, it's still a lot quicker.

Edit: And yeah, when I upgrade to the better limited slip, I may look into the 4.08's too. The 3.91's are barely even noticeable on the highway, even if it went up another few hundred rpms it would still be fine.

hbenet

iTrader: (31)

Justin, who's making the HLSD that you mentioned that is coming out later this year?

Justin@IOS

iTrader: (3)

I'm not sure who's the actual manufacturer yet, but it should be available through Nissan Motorsports.

Fluid1

iTrader: (19)

Good thread.
Who makes the 4.08?
Have you not looked into the Quaife?

Cannysage

iTrader: (29)

interesting thread. I didn't know the aggressive gearing of a 3.91, raises the rpm by only 300. any rpm numbers on a 4.08?

68Stang

iTrader: (7)

After doing gears in my Mustangs (4.10s), I've been toying with the notion of doing gears in the Z. What needs to be addressed as far as speedometer recalibration, or is that even an issue with these cars?

Justin@IOS

iTrader: (3)

Nissan. And I did look into that and the carbonetics limited slip. I held off because the other unit should be out soon. I'd like to see how the lesser expensive (or at least it's supposed to be) unit compares to the more expensive quaife setup. I'm hoping that it'll be a nice alternative to the quaife, at a much cheaper price.

Well, at 80mph it's only about 300rpms. 80mph goes from ~2825 stock to ~3125 w/ the 3.91's. The 4.08's would bump it to about 3250rpms at 80mph (rough numbers on all these rpms).

Increasing the speed to 120mph changes means a larger swing of 4400rpms / 4850rpms / 5075rpms.

It's really not that big of difference until you get up over 100mph and even then it's still not THAT bad.

Check this thread for more info too: https://my350z.com/forum/engine-and-drivetrain/301451-4-083-gears-final-drive-installed.html

The car measures vehicle speed off the wheel speed sensors, so there's no adjustments necessary.

68Stang

iTrader: (7)

Cool! Thanks Justin. The Mustangs use a speed sensor in the transmission, so you either have to wire in a "speed cal" (signal buffer box), or go the less reliable route and install a new plastic gear into the sensor.