Why the E46 M3 Diif so heavy?

[Cubieman]

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.

Yeah, something to be said for that, my buddy can't find a machinist to touch his S85 block due to a high silicone content I guess. Not sure if that has anything to due with the aluminum or not..

[sapote]

Yeah, something to be said for that, my buddy can't find a machinist to touch his S85 block due to a high silicone content I guess. Not sure if that has anything to due with the aluminum or not..

Maybe the cylinder wall coating has high silica.

[E46 M3]

Why's everyone always hell bent on ruining the weight distribution, part of the package that makes the E46 great.

[digger]

Maybe the cylinder wall coating has high silica.

yes it is Alusil

[digger]

Why's everyone always hell bent on ruining the weight distribution, part of the package that makes the E46 great.

i'd rather be 50kg lighter and slightly front bias CofG rather than be 50kg heavier and perfect balance.........lighter is better than perfect balance

[mrgizmo04]

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

So what's the theory?

Sent from my SM-G950U using Tapatalk

[sapote]

So what's the theory?

The theory is if BMW lengthen the Diff long enough to lower the push/pull force on the floor then maybe aluminum diff housing can handle the stress.

Most transaxles are aluminum housing -- I haven't seen a steel transaxle in my life yet -- and their longer total bodies convert the output torque to lower force applied at the floor mounting points. A shorter diff as the M3 converts the output torque to very high push/pull force applied on the sub-frame and the same reaction force wants to break the Diff housing, so stronger steel was used.

[Tbonem3]

i'd rather be 50kg lighter and slightly front bias CofG rather than be 50kg heavier and perfect balance.........lighter is better than perfect balance

But you'd rather be 50kg heavier if that weight were low, like a diff/muffler. Or, you'd rather remove 10kg from the top of the car than 50kg from the bottom, for example. You'd sooner spend $2.5k on a CF roof, than a titanium muffler, for lap times' sake.

[digger]

But you'd rather be 50kg heavier if that weight were low, like a diff/muffler. Or, you'd rather remove 10kg from the top of the car than 50kg from the bottom, for example. You'd sooner spend $2.5k on a CF roof, than a titanium muffler, for lap times' sake.

id still rather lose 50kg from something at height of axle than 10kg from the roof

[Tbonem3]

Well, 50kg is a big number, but there is a point not far from 50kg where you wouldn't. This is all for arguements sake. I'm not a mathmetician, but it can be expressed how important location of weight is.

[digger]

Well, 50kg is a big number, but there is a point not far from 50kg where you wouldn't. This is all for arguements sake. I'm not a mathmetician, but it can be expressed how important location of weight is.

if maximising cornering grip is a priority then sure there is a point where a lesser mass change at high CofG is more beneficial than a higher mass change at a lower CofG. In most circumstances id take the lower mass.

in any case no matter what type of racing you are doing you would take 20kg out of the diff if you could while your opponent couldn't, even though it might make the marketing department upset.

[sapote]

Any mass reduction will help the car accelerates and brake faster on the straight, and less mass at higher location helps the car corners better.

[usdmej]

Why's everyone always hell bent on ruining the weight distribution, part of the package that makes the E46 great.

when given more breathing room ($$$) to lighten the CSL, you can see that BMW chose not to reduce weight in the rear even tho they had the resources to (cf front bumper but sheet molding compound trunk out back, lightweight muffler teased but ultimately not used)

[bigjae46]

But you'd rather be 50kg heavier if that weight were low, like a diff/muffler. Or, you'd rather remove 10kg from the top of the car than 50kg from the bottom, for example. You'd sooner spend $2.5k on a CF roof, than a titanium muffler, for lap times' sake.

The problem you will run into is if a lack of adjustability to compensate for any imbalance created. For a racecar with an adjustable suspension and aero, you absolutely lose weight. You can rebalance the car with suspension, aero or ballast later.

Street car - that is much more difficult. Adjustability has compromises - usually reliability, cost, and NVH. I'd also doubt that anyone would notice unless you are really pushing the car.

I don't understand the question. The E46 M3 was designed in the 90's when BMW was MUCH different. They were becoming more of a mainstream luxury brand AND free maintenance was becoming a thing. Using an aluminum diff case to save weight in a 3 series...no one would have given a flying fock back then when it comes to selling cars. So add in the added cost, complexity, warranty issues...would be my guess why BMW used a heavy iron case.

Imagine a 50 year old Karen buying an SMG convertible back in 2001...do you think she would be like...oh this car has an aluminum diff case? SOLD! Fact...most people bought M3s because they were the most expensive and nicest 3 series. Not because it was a performance car.

If you really want to save weight and lower cost, run a non-M rear end. Lighter axles as well. Only downside is that an LSD conversion is not so easy. The E46 case is narrower than the standard 188mm case. I believe you can use a regular 188mm LSD from an E36 and assemble the unit inside of the case. Doable...much more of a PIA though working in a confined space. Much harder if you have fat hot dog fingers. Little girl hands would probably help a lot here.

You'd have to:

1. Assemble the LSD
2. Check carrier preload
3. Disassemble and remove the LSD
4. Set the preload on the pinion bearings
5. Assemble the LSD and then check backlash.

AND PRAY that you don't have the make a pinion shim adjustment. Then you'd have to disassemble the LSD to pull the pinion out to change out the pinion shim. Disassembling the LSD isn't hard at all. The biggest challenge is being clean.