Differential Swap 2.93 to?

[Hornung418]

Have to drop the diff to replace the seal on my cover :(

So instead of replacing the cover, I think I will replace the whole diff. What should I choose? I'm well aware of Bokchoys (http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm).

RootedDROIDXstatus. Come at me, bro.

[bullfrogs_M3]

M3 rear diff FTMFW!!

[Hornung418]

Yeah...I've was looking to do the M3 rear swap, but I don't have a 6 spd. I don't think I can source all the necessary parts for a reasonable sum and do the work myself in the limited time between work and play. Plus a 3;62 LSD would be nuts at highway speed...

But now that my diff took a shit and has to come out, it needs to be done soon and If I'm going to have it out I'm going to do it right. Doing it right = Subframe Bushings, RTABs, Center Bearing (which I have discovered is the cause of my vibrations on the highway) and Drive Shaft Flex disk will all be replaced. Maybe I can even put my $70 at Turner to good use with some Sway Bars...:shifty

So the question is what diff should I look for?

[az3579]

Personally, I think stock. The car isn't a horsepower demon and unless you go Forced Induction, it never will be, so methinks you should keep the stock ratio in there, use the car as a nice daily driver, and save up for something with power if that's what you want. Otherwise, keeping it the same will keep the costs to a minimum, and the car will most likely end up a little more reliable (lower rpms are better for the engine when driven daily). If anything, rebuild same ratio with an LSD...

[Stu]

It really depends upon how much you care about gas mileage and top speed. You can get a super high differential if you want to, but sacrifice top speed and mileage.

[mimalmo]

3.07 or 3.46

[zhpnsnv]

3.46 looks like a reasonable alternative. Not sure about for your car, but many have said and written that this is what the ZHP should have come with from the factory.

[static667]

I'm with Botond. Stay with the stock ratio but see about making it a LSD.

[SoarinZHP]

Go with stock. I had a 325i that I put a lightweight flywheel, performance clutch and a semi-organic high performance disc. The car was a lot quicker, but did not drive anywhere near it did bone stock. Kinda ruined the balance in a car BMW is known...

[Hornung418]

So just reseal a 2.93? It doesn't make sense to me that if I have to drop the whole thing, that I wouldn't put something better in it's place. It's bad enough that the gasket failed and my diff took a huge crap on my driveway...

If I had a 6th gear, I would consider a 3.46 in a heart beat, but cruising at 3446 rpm doesn't sound fun...I do want an LSD, but all really involves is dropping the Differential and replacing the Ring and Pinion on the new LSD unit. The issue here is that using an LSD on anything below 3.15 is pointless and unrecommended. Therefore I would need to find a shorter Differential to really make any sense, but I would like to do it right.

And BP, not every car cruises at 2.5k rpm. Early 323s cruise at 3.5k rpm so engine wear is not an issue in this case. To me it's a matter of exhaust noise, granted I have an already quite car, but for the future I would like to be prepared. :devilish

[Johnmadd]

3.46 looks like a reasonable alternative. Not sure about for your car, but many have said and written that this is what the ZHP should have come with from the factory.

This is what I would go with. You'll probably lose 1 mpg, but you will have a big jump in acceleration.

[ZSP-Mafia]

I have the 3.38 from an auto. I think it's a good compromise. I think my old 2.93 is still sitting around if you need to replace your diff.

[Hornung418]

Thanks for your input, Jimbo. I couldn't remember if you went with the 3.38 or the 3.46. I don't think I've shredded the Ring and Pinion yet, though. How is your gas mileage with the 3.38? You are cruising at 3.3k rpm, right?

I've seen 3.15 and 3.38 for sale on e46F and eBay for decent money. And a Kaaz LSD shell for $900 on e46F!!

[ZSP-Mafia]

I average 21-22, with mostly city driving. I think I'm around 3500rpms at 75-80

[Johnmadd]

Everybody mpg's are different. I average 28.6. Power over money.

[M0nk3y]

3.62 :shifty

[az3579]

The issue here is that using an LSD on anything below 3.15 is pointless and unrecommended. Therefore I would need to find a shorter Differential to really make any sense, but I would like to do it right.

Using an LSD is never pointless; I don't know where you got that from. An LSD is an LSD, regardless of what ratio it is, and personally I would take an LSD over ANY open diff, regardless of what ratio the open diff is.



And BP, not every car cruises at 2.5k rpm. Early 323s cruise at 3.5k rpm so engine wear is not an issue in this case. To me it's a matter of exhaust noise, granted I have an already quite car, but for the future I would like to be prepared. :devilish

So what exactly are you going for here? More engine noise or less? The taller-geared diff will help reduce engine noise.
3.5k rpm to me is waaaaaaaaaaay more than any car needs to be cruising at. That is what I call high-strung, and this is the one attribute I hated with my E30. Even with the 2.93 in it, it revved at 3krpm at 70 because of the gearing of the ZF S5D320-Z transmission.


Do what you will, you know this side of it now. It seems to me that your priority is better acceleration, in which case forget the 2.93. Someone here said the 3.46 I think is a better compromise; I personally don't believe in compromises. Get what you want and not "settle" for anything. :)

[Hornung418]

Thanks for your input, gents. I'll do a little more digging later tonight to see what's in the area. I should have a decision by this weekend.

RootedDROIDXstatus. Come at me, bro.

[Hornung418]

Found some info regarding a 6spd swap. Will post later today after work.

RootedDROIDXstatus. Come at me, bro.

[Hornung418]

Crazy good DIY Automatic => 6 Speed Swap (http://www.e46fanatics.com/forum/showthread.php?t=790149) from Titanium Cranium over at e46F. Not in the cards at the moment...but I thought I'd share. I think I'm going to opt for a 3;38...if I can find one. Then after a few drug studies before school starts I should have the cash for the LSD, which would only require me to use the Ring and Pinion from the open diff to the new LSD :) Thread regarding rear subframe beef up will follow shortly once I do more research. The clunk needs to go ASAP!

In other news...This Friday is Pay Day! :biggrin

[Johnmadd]

^hmmmm, drug studies and Lsd should bring some new site traffic.

[Hornung418]

LMAOOOOOOOOO! John...I'll take any drug for money ;)

[Johnmadd]

Rofl