Originally Posted by Pave Dew
Be careful here as CDV upgrade on non M cars is definitely worth doing. However, on M3 at least the CDV is full bore. Assuming 1M is the same then CDV swap out would yield little or no benefit.
I upgrade to an M3 CDV on my e91 335i and difference in clutch feel was night and day.
However, clutch pedal stop mod is worth doing to reduce the clutch travel.
I fitted the BMS one and it's good as its got packers so as you can adjust to best suit yourself and make sure there's no dragging of the clutch.
Just my 2 cents worth.
I have seen some post on the M3 forum where the early e9x M3 did not have a CDV restriction inside the adapter/valve. While later cars DID! I know M cars in the e/36, e46 and e39 M5's had a cdv. So... I think we need to see some testimonials first. But I suspect bmw puts these crappy CDV's on all their cars - including M cars. And including the 1M.
This is such a worthwhile must have mod that its worth having a look! You can not tell until you get it all apart though. Even so... its worth the effort.