Makes me smile from 0-60mph!! There's a 1200 mile break-in period so I can't really get the full effect, but I can definitely tell. Cold air intake, flow through exhaust and new sofware coming very soon........

Nice, I've been thinking of this, but I'm waffling between this and the 4.10. Keep us posted on your mileage.

wouldn't the 4.10 need 3rd gear to hit 60? Pretty inefficient to have to change gear twice to get to 60...

Nice! Congrats! The lower ratio diffs are always more fun :redspot

wouldn't the 4.10 need 3rd gear to hit 60? Pretty inefficient to have to change gear twice to get to 60...

If I were frequently doing 0-60 sprints for magazine stats testing, yeah, that'd be a hassle. Going from a stop to exactly 60mph isn't something that comes up often in day-to-day driving, though. Accelerating while moving is more common.

Where I'm conflicted is another Z4M owner says the 4.10 eliminates the need to downshift; I kind of like downshifting.

Makes me smile from 0-60mph!! There's a 1200 mile break-in period so I can't really get the full effect, but I can definitely tell. Cold air intake, flow through exhaust and new sofware coming very soon........
Wow that's a long break-in for a diff. Isn't it usually something like 300 miles for rebuilds?

Wow that's a long break-in for a diff. Isn't it usually something like 300 miles for rebuilds?

1200 does seem a bit long. Had a 500 mile break in on a fresh lsd for the Z4. Better safe than sorry though. They requested 1200 for some reason.

1200 does seem a bit long. Had a 500 mile break in on a fresh lsd for the Z4. Better safe than sorry though. They requested 1200 for some reason.
Often it's to break-in the driver.:D

If I were frequently doing 0-60 sprints for magazine stats testing, yeah, that'd be a hassle. Going from a stop to exactly 60mph isn't something that comes up often in day-to-day driving, though. Accelerating while moving is more common.

Where I'm conflicted is another Z4M owner says the 4.10 eliminates the need to downshift; I kind of like downshifting.

I guess you are right, and the 4.10 would eliminate the need to downshift, but if you do downshift, its even faster. So you can still indulge in one of your favorite activities ;)

This is a mod that I've been seriously considering as well. What did the Dinan 3:91 run you, and did it hurt your mileage to a significant degree?.... Thanks!

It cost about $3,600 installed. The rear diff from Dinan was about $2599 plus NC tax. To install at the dealer icluding shipping from Dinan and shipping my rear diff. back to Dinan was about $875. Dinan is running a 10% sale right now, so I should get about $260 back, so net about $3,300 and change. My gas mileage has definitely taken a hit. I haven't checked it yet, but thats not an issue for me. The car is not a daily driver, only driven on the weekends.

Thanks!

Next to a supercharger this is the best performance upgrade hands down.

My gas mileage has definitely taken a hit. I haven't checked it yet, but thats not an issue for me. The car is not a daily driver, only driven on the weekends.

I'll be interested in your fuel numbers - mine is a daily driver, and I was only considering the 3.91 because I'd heard that fuel economy was still sensible in 5th and 6th on the highway. If fuel economy's no object, why didn't you go all out for the 4.10? They're the same price...

I am seriously considering the 3.91 diff as well. Can you tell us anymore about how it changes the way the car drives?

ahhh 1200 mile break-in on the diff... i thought you meant you hadn't reached the 1200 mile engine break-in. i was like wow, you don't waste any time, do you :)

The 4.10 was not even an option for me. The 3.91 only increases RPM between 200 and 300 rpm at cruising speeds. I've been told the 4.10 is much more drastic than that and reduces top end speed. I've only been able to drive the car twice since I had it installed, so I really can't comment too much on aspects other than acelleration in the lower gears.

The 3.91 only increases RPM between 200 and 300 rpm at cruising speeds. I've been told the 4.10 is much more drastic than that and reduces top end speed. I've only been able to drive the car twice since I had it installed, so I really can't comment too much on aspects other than acelleration in the lower gears.


It does. I put a 4.10 in my 530. It originally had a 3.46. The ratio is great for this area with all the torque, but the top end does suffer. Adverage highway speed is about 75mph, and anything over 85 doesn't happen for very long due to traffic.
If a person does like the cruise at high speed I wouldn't recommend anything over a 3.91 or even a 3.83 ratio