drawbacks of lightweight flywheel

what are the drawbacks to a lightweight flywheel?
esp on a motor like the m30, which has a dual mass,
for the sole purpose to smooth the engine out?

i'd imagine that the advantages are less parasitic
drivetrain loss, quicker throttle response, basically
faster engine revving (so rev matching would be
easier)

but what are the cons? i spoke with some one
who said they had a 11lb flywheel on a nissan
and it was tough to get moving from a stop...

and bmw are supposed to be smoove, so how
rough will the m30 be after u take away its
dual mass?

final question, what are the options for swapping
out the dual mass? i've heard e28 swaps, and i've heard
e34 m5 swaps....
in fact rob, from uuc suggested doing the e34 m5 clutch
swap and getting a lightweight m5 flywheel from him...

Last year I put the 8lb UUC Flywheel w/M5 clutch in my 525i, I love it. I get some gear chatter with the AC on when I'm waiting at a light, but otherwise I'm happy.

The best pro is that the engine winds down faster, so it's easier to shift and match revs. That and it was cheaper than a dual-mass flywheel!

Biggest con is that you have to get used to the lighter mass, because it is quite significant. It's quite a bit easier to stall out with this setup, but like anything else, you get used to it after a while.

Some people aren't comfortable with this setup, the tradeoffs aren't worth it I suppose. I've been quite happy with my it, and from what I read, my gear rattle is mostly due to slop in my transmission. The problem is hit and miss, a lot of the E36 guys only see it on a limited basis, and sometimes not at all. I hope to be able to replace the motor/transmission this year and then it won't be a problem.

Can't comment on an M30 install, but I expect the results to be similar. Whether or not you like it? Guess you won't know until you try :)

It's totally a personal preference thing. Like I said in the PM, the 11ish pound flywheel on that 300zx was way too light IMO. With a super-heavy on-off switch for a clutch, it made driving it too much effort. And I like effort. :)

In a semi-luxious car like an E34, I personally prefer to lean on the side of a semi-luxurious driving experience... I mean if I wanted to drive a high-effort sports car, I could've kept my RX-7...ya know? :)

But hey, if Aaron likes his 8lb setup, maybe it's not as drastic in our cars as it has been in other cars I've driven. Either way it's just a matter of what you are willing to put up with in your car.

e28 setup works very well. To light and you are having trouble moving off the line smoothly. The UUC setup is nice, but its also about $1500 setup when you are done.

yeah the price is a factor, but i'm planning for the future
as i'd like to go turbo....so having a little more holding
power with the m5 clutch will be a plus

any other thoughts folks? i'm sure more of you have done
the swap? right?

hey bahn, message me when you get back, i have a guy for you to talk to regarding the flywheel.

I replaced my dual-mass in my previous e34 - 1992 535i. I suspected it was bad (rattling) and was looking for a performance gain. I worked with Jim at Metric Mechanic and used an M5 clutch with his lightened flywheel. No negatives, all positives - cheaper, freer reving, and a little quicker. I still had some slight rattle, though (reverse idler gear in the tranny according to Jim). I would do it again if I were in the same situation (rebuilding tranny and replacing clutch). Mark

awesome info that's mark

i was looking at MM's site and they have a lot of tech article...
they mention a harmonic balancer...is that something they add
to the car or what?