dinan 4.10 diff installed and broken in

[dcstep]

Originally Posted by Richbot

I've always wanted to do this and every time I cruise on the highway for any extended period I am cured of it and start wishing for a tall 7th gear with a shorter 3-6 gearset, but that's called a DCT and I don't like the downsides that come with that, soooo oh well

Noise is not a problem when cruising. There's a fuel economy penalty, but that's all, when cruising.

I put on throttle bodies, exhaust and the 4.10. The gear was, by far, the best performance improvement, for autocross and around town driving.

[srmast1]

Originally Posted by dcstep

Noise is not a problem when cruising. There's a fuel economy penalty, but that's all, when cruising.

I put on throttle bodies, exhaust and the 4.10. The gear was, by far, the best performance improvement, for autocross and around town driving.

I've been wanting to do this for years, it's just that I don't daily my car and because of that I have always had trouble justifying the cost.

[srmast1]

Originally Posted by SAMM3Y

I'm 90% positive the turner one comes from diffsonline.com. Having said that I have a turner 4.10 diff from one of their GT cars which is sweet and sounds awesome on deceleration with an os giken LSD. I'm not aware of a stock 4.10 gearset but there could be.

Do you have that diff for sale?

[SAMM3Y]

Originally Posted by srmast1

Do you have that diff for sale?

This is the only bmw part number I know of, 33108321899 I think it might be only for the smg trans in the e46 and e60 m3/5. Yeah I'm currently running it and no it's not for sale, I haven't noticed a short 1st gear I've noticed it's redlining in second at 60mph and it cruises on the freeway in 6th at 74mph @3500rpm with a 295/30/19 rear. Not terribly different, If I think it's only a 6% change in ratio.

[srmast1]

Originally Posted by SAMM3Y

This is the only bmw part number I know of, 33108321899 I think it might be only for the smg trans in the e46 and e60 m3/5. Yeah I'm currently running it and no it's not for sale, I haven't noticed a short 1st gear I've noticed it's redlining in second at 60mph and it cruises on the freeway in 6th at 74mph @3500rpm with a 295/30/19 rear. Not terribly different, If I think it's only a 6% change in ratio.

Oh ok, thank you Sammy!

[Richbot]

Forgot the other thing Most 285/30-18 rear tires get you 98% of the gear reduction you get from going to a 4.10 for what it’s worth.

Rpm at 60mph in 6th .872:1 with stock 3.85 rear ended on 26.3” stock rear tire: 2574

60mph with stock 26.3” tire and 4.10: 2742

60mph with 24.8” 285/30-18 and 3.85: 2730

On some tracks you’d want both the shorter rear tire and the shorter diff for tweener corners or slow corners where you don’t want to drop to 2nd, but if you just want shorter final gearing there are other options. A 285/30-18 on an 11” or 10.5” wheel is plenty for an NA car, and can be run square with careful offset selection

[dcstep]

Originally Posted by Richbot

Forgot the other thing Most 285/30-18 rear tires get you 98% of the gear reduction you get from going to a 4.10 for what it’s worth.

Rpm at 60mph in 6th .872:1 with stock 3.85 rear ended on 26.3” stock rear tire: 2574

60mph with stock 26.3” tire and 4.10: 2742

60mph with 24.8” 285/30-18 and 3.85: 2730

On some tracks you’d want both the shorter rear tire and the shorter diff for tweener corners or slow corners where you don’t want to drop to 2nd, but if you just want shorter final gearing there are other options. A 285/30-18 on an 11” or 10.5” wheel is plenty for an NA car, and can be run square with careful offset selection

Yes, for autocross, running a 4.10 with 18" wheels, you very seldom have to shift to third, although you may hold the redline for less than a second at some parts of the course. Using a chip that moves your redline to 8600-rpm is also helpful.

I don't think that the 4:10 makes sense for a track car, in general, with an 18" square setup, which I like to run. Of course, it's going to be track-dependent. On a faster track, getting some extra oomph in higher gears could be useful. Depending on the track, once you're rolling, are you adding shifts or saving shifts? That determines how good it is for track. In general, I think 18" square is the way to go for track. For AX, I think 4:10 plus 18" square is the way to go.

For street, I like 4.10 pluse 18" square in summer, staggered in winter. (I'm in Colorado).

[Richbot]

4.10 + 285/30-18 = ~170mph top speed in 6th, the 2-3 shift is the only shift that isn't perfectly spaced (too big a drop) and you basically drive a 4-speed h-pattern with no danger of 2-3 3-2 moneyshift fails. And the car will be measurably faster in-gear in 3rd and 4th where you are most of the time, especially in those annoying digs out of slower corners in 3rd where the S65 is a bit gutless

The GT4 got the 4.1's and iirc a ~25.5" rear tire for an effective change of about 10% sooooo BMW Motorsport at least thinks it's a solid idea to use the 4.10's on track, heh

You're usually in 3rd and 4th on a track, the 4.1's will just change where the shift happens, same with 4th-5th, only the real long straights allow an NA car to get to the top of 4th, you might need 4-5 at start/finish instead of right before the brake zone and you'd have to be somewhere like Daytona to need 6th, but who cares, that extra in-gear acceleration is a big difference-maker

[Dave07997S]

4.10 gears along with a 8600rpm rev boost is a nice match. Usually gears are done as a package deal. You run a cam that moves the torque and powerband higher in the rpm range, gears can help you offset the loss.

I think a FBO S65 along with a 8600rpm boost is a nice package, throw in some cams for more top end charge and it really would be a nice kick in the pants.

The OEM 6MT 3.85:1 to 4.10 is not that great of a change but it will help.

Dave

[pbonsalb]

Still hoping to read some data on cams. Very, very little so far. These cars already have strong top end power and modest low end power so I would want to know the trade off for my daily driver purposes (track cars would trade more).

[Dave07997S]

Originally Posted by pbonsalb

Still hoping to read some data on cams. Very, very little so far. These cars already have strong top end power and modest low end power so I would want to know the trade off for my daily driver purposes (track cars would trade more).

Yea that one thread fell off the cliff. He said the car is now making horsepower but never came back on results. Also, I wouldn't want to raise my rpm until I get the RBs done.

Dave