I've posted a few other notes and impressions in the autocross thread in the track forum but I figured I'd put it all here for searchability's sake.
Back in March, I ordered a set of MCS ( http://www.motioncontrolsuspension.com
) 2-way remote reservoir dampers for my E90 M3. They arrived in very early May or very late April ahead of the promised lead time, and I've finally got them on the car now. I ordered them configured for SCCA Stock-class autocross competition, which requires the use no more than two external adjustments, stock ride height, and use of stock springs and strut mounts, which means they were machined with a shoulder and a welded ring to accept the stock spring perches. This is similar in concept to what JRZ made for the VS Motorsports T2 E92, and in fact I ordered this MCS setup through VS Motorsports in the Chicago area, which was a great experience. Top notch customer service and good pricing.
First of all, I can't say enough about how responsive and helpful Lex at MCS has been in working through this and getting them on the car. The stock spring perches do fit, but when I was unable to get them on straight with the tools in my garage, I just shipped the whole thing with the stock springs and mounts and everything back to MCS, where they pressed the perches on, reassembled everything, and I was able to just install everything as an assembly. They really were more of a press fit, but that's good, that means they aren't going anywhere. Service after the sale is one of the most important parts of buying one of these pimp shock setups and MCS delivers.
I've had the shocks on the car for a few weeks but just got the struts on the car of yesterday morning, and I will have an autocross in a few weeks to really try them out. Having already had on event on the car with just the rears, the adjustment range and performance is really amazing. Rebound goes from softer than stock to waaay stiffer than stock to the point where you can pack the car down on the bumpstops if you want to. Compression is similarly very wide-ranging and has a big impact on transient response, I'm still playing with it.
Behavior over big hits and mid-corner bumps is where the car is really transformed. You really, really have to try to upset the car now, and the skating over mid-corner bumps that was present with the stock dampers is just gone. Throttle oversteer is still available whenever you want, but you don't need to tiptoe over bumps like the stock setup requires.
The other really neat part of these things is the nitrogen pressure adjustability, which is a feature of most remote reservoir dampers. I've got them set at 250psig right now and the car seems to really like the extra "spring rate" from the nitrogen lift, which makes sense with my car limited by the stock spring rates. Interesting side note, With about 75 psig in the canisters, the car rides about 1/4" lower than with the pressure set at 250. I'm happy to report that the canisters appear to hold pressure just fine as well, I'm probably losing more pressure just checking the pressure than is actually bleeding down.
I'm running 295/30-18 and 315/30-18 Hoosier A6's and preventing rollover is key when you're stuck with near-stock camber (-1.4 ish with the pins pulled) running bigass tires, so the added roll resistance should be a big help, especially in the front, where I might be able to soften the front bar while maintaining roll stiffness, which will help with mid-corner balance. Lots of fun stuff to play with. The tire wear will tell the tale at the next event. Actually picked up about 1/8" of additional tire clearance to the strut with this setup, which is nice to have. Might be room for 305's on the front now.
For the street, I've settled on about 100psi in the canisters for the slightly lower ride height, and 3 clicks from soft on the rebound all around, with 2 clicks of compression in front and 4 in the rear. This seems to keep the control over big hits effective without inducing any head toss over rough concrete. Turned all the way down, the car feels underdamped, but it might be ideal for a long freeway trip as it rides pretty damn nice with them turned down, with the only harshness coming from the relatively stiff M bushings. There's a noticeable difference between each adjustment point, which I'm very surprised by as I was expecting to need 3-4 clicks to notice a difference with all the soft bushings, heavy car, floppy springs I have going on.
The MCS setup in total weighs about 8 lbs more than stock. This is partly because of the remote reservoirs and hoses and partly because the struts use a steel body instead of aluminum. Most of extra weight is in the struts themselves. The shocks are within half a pound of stock including the canister.
Mounting the canisters was probably the most difficult part of the install except for getting the spring perches on the struts. I ended up routing the rears through a notch cut in the trunk vents on each side, didn't even need to cut the fender liner, and zip-tied the canisters to the carpet which I'm required to retain in Stock class. It was my best solution for ease of adjustability for both compression and nitrogen pressure and keeping them out of the way of cargo with the length I had available. The fronts are routed up along the brake line with some cut fuel hose protecting them from abrasion against the brake line bracket, and the canisters were placed by the windshield drains. This is really more of a friction fit, using some leftover racecar fuel cell foam to hold it in place. I didn't want to have to cut and re-ziptie the canisters every time I want to adjust pressure, and this still allows easy access to the compression adjuster if needed.
Will report back with impressions after I've competed on them a few times and have a better idea what I like for autocross settings. I have a feeling I won't be far off my street settings.
tl;dr: Highly recommend MCS for your E9x Pimp Damper needs. See below for out-of-focus photos