As far as I know, the M3 mounts are still fluid filled. The Bimmerworld and Group N mounts are solid rubber. Turner claims the Group N mounts are 30% stiffer but don't indicate what this is relative to. I'm sure the BW mounts are in the same ball park as far as stiffness. I can tell you that my car literally jumps to life when started and there is more noise and vibration transmitted than is generally found acceptable on any new BMW (kind of reminds me of an exhaust upgrade). I've haven't run either of the M3 mounts in my car but I think it's safe to say these motorsport mounts are significantly stiffer than anything produced by BMW for street use.
Originally Posted by McSpeed
Any idea how the Bimmerworld mounts compare to either of the M3 mounts?
FWIW, I have some compression resistance data for a couple of different stock mounts that was provided to me by a manufacturer so I'd rather not post up the graph but the older M3 mounts look to be roughly 10% stiffer than the 330 mounts (the variation isn't 100% linear).
04 IR 330i ZHP | ESS TS2+ SC | MagnaFlow "headers" | KMS 3.64 LSD | AST 4100 550/650| APEX ARC-8 18x9 | H&R front sway bar | Vorshlag camber plates, RTAB limiters | TMS subframe & swaybar reinforcements | UUC SSK & DSSR | UUC TM & TME | BW motor mounts | Dinan strut & shock tower bars | vaio 4-bolt oil pump