Why the E46 M3 Diif so heavy?

[sapote]

Why the M3 diff was made out of heavy steel instead of lighter aluminum alloy? More powerful car such as the 6L V12 DB9 has the aluminum diff housing.
Something to think about as the DB9 has no problem of handling the pinion/ring from exploding the AL case.

[Tbonem3]

Cost

[bigjae46]

Noise
Reliability

All stuff that BMW drivers bitch about.

The engine block is iron, could have made that from aluminum as well.

[sapote]

I have a theory, something to do with this odd shape Porsche 911 front Diff:

[Jimbo's M]

The engine block is iron, could have made that from aluminum as well.

BMW M motor engineers at the time decided that an aluminum block would not have the durability of an iron block with such a heady redline. This engine has almost the same piston speeds of the BMW F1 V-10 of the day, so aluminum was ditched.

[bigjae46]

BMW M motor engineers at the time decided that an aluminum block would not have the durability of an iron block with such a heady redline. This engine has almost the same piston speeds of the BMW F1 V-10 of the day, so aluminum was ditched.

My point was...not really seeing the point of this question? This car was designed over 20 years ago when tech and manufacturing was very different. I'm not sure what the proposal is here? Make a forged aluminum diff case?

[sapote]

My point was...not really seeing the point of this question? This car was designed over 20 years ago when tech and manufacturing was very different. I'm not sure what the proposal is here? Make a forged aluminum diff case?

Many sport cars older than the E46 with aluminum transaxle: porsch, Lotus, Renault, Ferrari, VW. It’s not the technology was not ready.

[Nuclear Rabbit]

e46 m3 had to do some cost cutting. Compare to e39 m5

e46 m3: iron block, steel rear subframe, all steel rear control arms, steel shock bodies
e39 m5: aluminum block, aluminum rear subframe, all aluminum control arms, aluminum shock bodies

although now that I think about it, they both use steel diff bodies, so maybe not

Maybe it's to give a strong center lift point for the rear?

[nahvkolaj]

Gotta distribute some weight to the rear somehow

[sapote]

e46 m3: iron block, steel rear subframe, all steel rear control arms, steel shock bodiesr?

It has all aluminum rear control arms
Drivers tried to reduce weight by opt for manual seats, sunroof delete, CSL trunk lid, etc, and the steel Diff is like 75lbs or more.

[Tbonem3]

The uppers are alloy, the bottoms are steel I believe.

It's already too easy to drop weight in the rear. I'd focus on the front end. Heavy diff and muffler is fine as it's low and in the back.

[bigjae46]

Many sport cars older than the E46 with aluminum transaxle: porsch, Lotus, Renault, Ferrari, VW. It’s not the technology was not ready.

The technology to produce the case on a large scale at a certain cost...absolutely was not available. Look at carbon fiber reinforced plastics. Modern tech has significantly lowered the cost of production for raw materials and finished products.

[sapote]

The technology to produce the case on a large scale at a certain cost...absolutely was not available.

Maybe, but they managed to produce million of VW aluminum transaxles, so the material and technology was there. I wonder if BMW have ever made aluminum Diff on any cars?

[digger]

same reason as the block is iron, cost. Both could have been alloy with appropriate development.

[Slideways]

For the engine, the iron block is much easier to machine during a rebuild than the Alusil blocks on the S62 and S65. I'll take the durability and easier rebuild factor over the weight savings.