M3 suspension, shocks, struts, springs...
now I know Alec isn't fond of this. But i've done the swap a few times.
#1 an M3 suspension is slightly taughter than the sport, but also, will ride slightly higher. My rationale. In the past now. 328ci, with 75k miles on it, sport susp. And for 150 bucks got M3 susp with under 10k on it.
Swapped well, was about 1/2 taller in front and 1/4 taller in rear (probably half that difference was the aging of the suspension). Car definitely handled better.
#2 Bought a 325i with stock suspension. i was getting seasick driving this thing. Swapped to M3 suspension. Lowered by about 1/2 inch front and rear, and much, much tighter. Handling was crisper as well as rebound was 1000% better. No floating, just nice firm M3.
My recommendations. If you have sport suspension and it's not worn out, or the M3 susp you can get is of similar milage, don't do it. If you have high miles on your sport susp and a low mile M3...will be worth it. If you've got a non sport susp - get the M3 susp, provided you can get it cheap. Remember you do have to get car aligned after this.
The technical issues.
1. Rear - direct bolt in. Hopefully you can purchase with top mounts too as they are much better than stock 3 series. The spring slips in and the shock bolts right in. Nothing to worry about.
2. Front - this is where the issue lies. The strut hat or top mount is M3 specific and your stock one won't work. So you need the entire strut, with spring and top eccentric mount from the M3 to make it work. Guys that have gone to coilovers will have removed this part, others with simple strut upgrades may not have. Without this part, the suspension is useless to you, and the part is i believe 90 bucks each at stealer...so unless you get the front hats don't buy the M3 suspension.
Now for the install, there is a trick, the eccentric top mount has an arrow that's supposed to face forward, with right on right and left on left. If you turn it (3 holes) so that the arrow is pointing towards the motor (inward) the alignment will be easy and more or less right on without any significant adjustments.
So yes after reading through this thread, and not seeing this info I thought it worthwhile to give you my experience. I do have an M3 (vert), and while the susp is not as balanced (lacking sways) in these other cars....it was definitely worth it...having purchased my sets for 150 bucks each.
09 135i crimson red, 07 x3 M sport pack, silver, 05 corvette, procharged..., 12 dodge ram