Lower E46 330 Motorsport Help

[cab01 0]

Just wonder if anyone has had any experence with Lowering E46 330 motorsport. I am looking for a 30-40mm drop from factory (already slightly lowered standard) but can't seem to get a straight answer from anyone on which spring will do the job. Anyone with experence please let me know. Thanks.

[Mike 1]

Welcome to the forum. One of our sponsors sells H&R springs and should be able to help you out. I think his username is SUSPENSION. Also, I shifted you're topic from general into the correct section.

Cheers

[central3 31]

Each to his own re lowering the 330MS - I had a long hard look at this - ended up taking the advice of a suspension shop who said "leave the hieght alone if you like the ride/handling (which I do) and "change to a set of Bilstiens if you want to get the car back to as new" - which I did ($1,050). Love the tightness of the (100,000 km) car now and think the ride hieght looks just right. I know this won't help but thats how it is for me.

[zenetti 0]

We have lowered plenty of E46 BMW's at work, but not a lot of Motorsport's for the following reason. Your Motorsport will probably already be 25-30mm lower than a standard E46 due to it having the factory lowered motorsport springs in it. Most lowering springs give a 40mm - 45mm drop from standard E46 (non-MS) factory height. In reality this means your car will only be lowered by another 15mm-20mm or so.

You also have to be careful not to go too low with your coupe as you run the risk of damaging your subframe.

Hope that helps

Edited April 7, 2010 by zenetti

[hybrid 1039]

You also have to be careful not to go too low with your coupe as you run the risk of damaging your subframe.

just a minor correction on this.

Lowering the car wont cause the subframe issue only running stiffer springs and driving hard all the time causes the front and rear mounts to rip the unibody mounts to subframe.

Its actually abusively hard accerlation and de-celleration (without brakes) that causes it. and only really from a stand still.

Racing it around a track a lot will also do it.

Hitting the bump stops (for being too low) causes trailing arm and upper strut tower damage which is a different problem.

[pjay 8]

The rear subframe is a known problem in the 46's. It's all over the internet, and lowering them more than the average Joe Bloggs does much speeds up their destruction.

[hybrid 1039]

Putting in standard run of the mill softish lowering springs wont cause subframe to unibody problems in a e46.

most of the comments on this issue are speculation from the internet panic patrol.

The problem is only caused by hard acceleration and de-acceleration which causes the subframe to put stress on the unibody / floor pan hard mount points. Metal fatigue sets in as any metal does when its stressed back and forth. Eventually the unibody / floor pan starts to tear. You can get the floor pan welded for a repair however it will just happen again. The best preventitive way around this is installing re-inforcement plating. Or having a new weld in floor pan section which needs to be obviously professionally installed by a panel beater with the right hi-voltage plasma welders as well as finished and re-constructed.

Hope this clears up the myth of 'subframe' failure for e46's which is actually unibody / floor pan failure.

[pjay 8]

I'm no expert at all, wasn't it the subframe mounting points?

[M3_Power 636]

I have said this before ...

if you are going lowering springs for looks then by all means do it (but on a motorsport? Really? those things are lower than the M3 from the factory), but if you are doing springs for handling then you won't get it from springs - period.

On the rear subframe mount failure.

The failure is in the Unibody as Josh has pointed out - the failure points are in the unibody floor where the rear subframe is bolted to it.

It is fairly conclusive now that the failure is a torque induced one - hence if you do a lot of burn out, a lot of drifting, do a lot of hard launches (including launch control) then the chances of tearing the floor out of your car is multiplied.

It is actually not a common fault for regularly tracked cars Josh (Thorney Motorsports in the UK have said this over and over again - unless of course you make it a mission to drive on the rumble strips all the time - none of their CSL cup cars have had rear subframe issues nor any uprated plates welded on and these cars take a real punishing).

There's actually a debate as to whether heavier springs help or exacerbate the problem - the consensus (and this is backed up by quite a few motorsport known folks) is that it does neither unless all the bushes are worn on the rear end (this includes the RTAB, the Rear Shock Top mount, and the rear subframe bushes). The consensus also seems to be that heavier springs (with correlating uprating of dampening and rebound characteristics will actually help against tearing as there's less oscillating torque forces acting upon the actual mount points when the rear end forces are limited to its design - i.e. up and down and not side to side or front to back). Imagine a seesaw and the subframe unibody floor as the fulcrum point of everything else - the more that everything else moves the easier it is for it to fall apart.

It appears also that the way BMW designed the rear end of the car is to have the RTAB fail first, followed by the Rear shock towers ... ect ect ... so keeping an eye on those two regularly WILL Help .. as the next ones to go are followed shortly by the rear subframe mount.

So uprating any of the first failure bushings simply moves the failure points to other components within the whole rear end system. I personally know which I'd rather have fail before anything else.

One thing that is certain and it's that SOLID rear subframe bushings WILL accelerate the failure.

Most post 2003 E46 will have had the new update rear subframe unifloor and these are known to be less prone to failures. Coincidental also is the fact that when the subframe failures were starting to be widely reported that BMW updated the RTAB design to a split shell design which are lot better and longer lasting.

And if words don't put you off abusing your E46s ... here's what's involved in a new rear unibody floor:

Still want to do burnouts and regular drifting in your bimmer?

Edited April 27, 2010 by M3_Power