Let's talk clutches

[kawstik]

Hey folks.

As I continue to transition my M from a daily workhorse to a dedicated track toy, my next endeavour is a clutch for my 6MT. It's on the way out.

My production date is prior to the 09/2008 update which means I'm looking at a new flywheel unless I source a refurbished / Luk original.

So I guess my question is, who has stuck with OEM / Luk replacements, and who has moved to a kit such as the Spec line? For those that went the 'performance' kit route, are you happy with your decision?

FYI - I'm not worried about extremes in the torque department. She's NA with bolt-ons and will stay that way.

Cheers.

[ricardofors68]

I haven't done mine yet, but when I do, I think going stock would be the way to go as I don't tax my driveline with the power that I make or the way I try to put it down.
Surprised to see that no one has chimed in. Did you try asking/searching in Engines, transmission, etc. forum?

[elim11]

Replaced mine w oem. No issues on the track. Same bolt ons mods only.

[Richbot]

What does the GT4 use? Looks fancy on the parts fiche

I agree stock seems adequate but it’s annoying to put stock stuff back in when something that might improve performance is about the same price because of the flywheel change

Might be worth a call to Bimmerworld and Turner. They both have experience running these cars in IMSA with the 6mt and I think clutches were allowed mods

[dparm]

Originally Posted by Richbot

What does the GT4 use? Looks fancy on the parts fiche

http://www.m3post.com/forums/showthread.php?t=393417

"Single-mass flywheel and 3-disc sinter clutch"


The actual catalog of parts is here, and there's a whole section for clutches, gearbox, etc.:

http://cache.bmwusa.com/Pdf_2f462d7a...9-8a17bf00572a

[kyrix1st]

Someone told me OEM clutch can hold up to 650hp SC motor no problem. I see no reason to go aftermarket.

[pbonsalb]

It’s the torque not the horsepower that matters and centrifugal don’t add as much torque as horsepower because the boost is just starting to develop in the midrange as the engine VE drops. 600 rwhp might give 400 lbs rwtq on an S65 with centrifugal supercharger. 400 lbs rwtq is no problem for an organic twindisk. For the race car, a single mass flywheel and triple disc might make sense, but not because it’s needed to hold the power of the 4.4L NA motor. It’s probably lighter due to the single mass and smaller diameter discs, plus getting rid of the dual mass removes some complexity. However, it’s probably not as pleasant to drive on the street as the stock clutch.

[kyrix1st]

Originally Posted by pbonsalb

It’s the torque not the horsepower that matters and centrifugal don’t add as much torque as horsepower because the boost is just starting to develop in the midrange as the engine VE drops. 600 rwhp might give 400 lbs rwtq on an S65 with centrifugal supercharger. 400 lbs rwtq is no problem for an organic twindisk. For the race car, a single mass flywheel and triple disc might make sense, but not because it’s needed to hold the power of the 4.4L NA motor. It’s probably lighter due to the single mass and smaller diameter discs, plus getting rid of the dual mass removes some complexity. However, it’s probably not as pleasant to drive on the street as the stock clutch.

I knew this comment would come up.

HP=torque[ft lbs]*rpm/5252. Since peak power is achieved at similar rpm with supercharger (I think) I say the term is interchangeable in this case.

[ThunderMoose]

Originally Posted by kyrix1st

I knew this comment would come up.

HP=torque[ft lbs]*rpm/5252. Since peak power is achieved at similar rpm with supercharger (I think) I say the term is interchangeable in this case.

I'll take it a step further.

Ever wonder why you basically get the same hp results on a dyno no matter which gear you run it in even though your gearbox is big honking torque multiplier? Because the formula for hp is

Hp = mass x velocity x acceleration.

HP is the only measurement that matters. As you pointed out torque follows the hp curve.

You will always get maximum available acceleration at peak hp at the crank.

[pbonsalb]

Ok. So why are clutches rated in torque not horsepower? If we go by horsepower, the clutch that works for the 600 rwhp centrifugal E90M3 might not be a good choice for my 600 rwhp turbo E36M3.

[kyrix1st]

Originally Posted by pbonsalb

Ok. So why are clutches rated in torque not horsepower? If we go by horsepower, the clutch that works for the 600 rwhp centrifugal E90M3 might not be a good choice for my 600 rwhp turbo E36M3.

You are absolutely correct on the clutch rating. Only reason I stated interchangeable in this case is we are discussing SC S65 motor with a similar torque curve as the stock engine-easier for most to understand the difference.

[MasterP]

I have a spec twin with light flywheel. It's evil. You need to give it a lot of revs when starting. Need a pretty aggressive blip on the heel toe when down shifting. Pretty rough on the NVH. You can hear the clutch chatter and if you have upgraded mounts it amplifies it. Revs up nicely once you're going so good for track use since you're never having to start from a stand still. Main reason I went with it was lower cost new than OEM and you can send them back to spec for a rebuild which saves on upkeep cost. I don't consider a streetable clutch.

[pbonsalb]

It might be easier to use if you increased idle rpm to around 900.