Rear end for FI

[BimmerScreamer]

So I always see people putting these low number diffs in their cars when they go turbo, why is that?

I want acceleration and love the way geared down cars drive. I have no problem losing top end speed. Would it be bad to run 4.10's with a turbo

[coolasacuc]

yeah.
depending on your choice of trans, you wouldnt have a first gear and i dont think you could build full boost until 4th. or first longer gear.
my 2cents

[Danny]

Lower gear ratio = more load on the motor = faster spool.

Or so I've heard.

[wagonizzle]

On an NA m20, a 4.10 rear will help the car rev more easily, and acceleration will be slightly better. This is with ~140whp. Once you add 100hp to that, the need for a short gear becomes less. In fact, the law of diminishing returns comes into effect: very short gears will zip right past your powerband, and you will spend more time spinning tires than you will accelerating. If you want a smoke machine, stick with the 4.10. If you want to go somewhere, perhaps a 3.25 would be more suitable.

[BimmerScreamer]

well my car is an iX so it has 3.91 all ready and the only other option is 4.10's

[Tchao]

I did the Eta LSD swap. It sucks.
I rather have 3.73 LSD again.

[BimmerScreamer]

what ratio is the eta lsd?

[Tchao]

2.93LSD (mine) but some also came in 2.73LSD

Way too long for the Getrag 260.

[TS87325IS]

I have the stock 3.73 lsd in mine still and it is fun , but I would prefer slightly lower like 3.46 or 3.25 would be perfect , 2.93 if you are running high boost would be alright too , but I am only running low boost.

[lostbeachbum]

We are running a 3.46 on our boosted car, It runs really well

[blueapplesoda]

3.23, 3.73....the stock 3.73 is very drivable on the street/canyons with lots of boost. But depending on what track I would be running at, I would change between the 3.23 and 3.73. Covers pretty much everything I need.

a 3.46 would be nice.

[bimma360]

I've got a 2.93lsd in the dinan turbo using 12lbs of boost. First gear goes very quickly... 2nd tops at 65mph, 3rd at about 110mph, and i've only had 4th up to 138mph at about 5000rpm... cant remember exactly.

I'd say that the perfect lsd for a car with my kind of boost would def be a 3.25 to utilize the torque a little better. But honestly? I love my 2.93lsd, the car is a highway monster and it just keeps pulling and pulling. And on the twist's i can pretty much stay in 2nd the entire time and be ready to upshift as soon as i exit turns. And then just stay in third on a strait all the way up to 110 before shifting again.

Dave

[Tchao]

^ Worst diff, IDK how you like it.

You will NEVER be on the top of 5th at ~205mph. Nor 150mph very much (if ever)
So why waste your gearing there?

It sucks ass on twisties, I road race my car with the 293 LSD and it was much crappier then with the 373 I had before.

A 325 would be better, but a 346 would be the most ideal.

[bimma360]

Well I really don't know, but I'd say in a high boost car by the time you reach full boost in 2nd you'd already have to switch into 3rd using a 3.46. Although, I'm just speculating here since I've never had a 3.46. I'm happy with the 2.93 bc I'm fully boosting through 2nd. And can go from ~25mph to 110 with only one shift in between. And am at full boost almost the entire time. I think as far as acceleration goes that makes up for the lower gearing. But that's just for my setup of course at 12psi. I'd like the 3.25 but I have other places to put money into at the moment.

[funcrew]

I have a mint low-mile 2.93LSD sitting in a box in my garage. I'm only planning to boost to 8PSI initially, and was planning to use this diff, since it's a daily driver and I do a lot of freeway time. It's not a case of needing 205MPH, but easy cruising and good MPG.

After reading Tchao's comments though, it sounds like this diff might be miserable at 8PSI. Crap.