[hryden]

Well, I blew out the clutch in spectacular fashion coming out of a turn over the weekend at Road Atlanta. I am sure it made for some interesting moments in the 911 behind me.



So now the question becomes, for a car that is basically a track / DE car, should I use the opportunity to replace the flywheel as well as the clutch? I have a stock clutch and flywheel in the car now. Anyone have any suggestions on what to go with as far as the clutch and flywheel, or should I just stick with stock parts?

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[flash]

lol - i fragged one at P.I.R. with a 911 turbo hot on my ass



there are a couple of options, and i've now tried them all.



the DMF (stock) works best on street, makes no noises or rattles, and holds up fine. it is the slowest to rev, and the most expensive to replace.



the 18lb single mass flywheel that rs barn sells is PCA approved for racing, revs faster, which helps gear matching, but causes a rattle in the transaxle at about 2300rpm. it is only a noise, and there are no signs of any damage. it can also cause occasional stalling when really cold, though this is extremely rare. you will need to balance it, along with the pressure plate (no matter what anybody tries to tell you otherwise)



the 12lb fidanza single mass flywheel is very similar in design to the rs barn unit. the rattles are more pronounced. the revving is much faster, and is the best performance increase, but is not sanctioned for racing. the cold stalling issue can be more frequent. it will also require balancing.



there are a few different pressure plates out there, ranging from 2500lbs (stock) to 3700lbs. i have the 3200lb unit and like it best, as it gives me very quick engagement. it is a bit stiff for some people though.



the only clutch disk out there that really works is the OEM disk. it is good for up to about 275hp. a relined kevlar disk can help with higher output engines, but won't last as long, and can chatter.



i hope that helps.

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[Cloud9...68]

The OP didn't say which organization he's going to race with, but I checked the NASA rule book, and it didn't say anything about flywheels, so it appears that you can use any one you want with them. Somebody please correct me if I've overlooked something.

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[Lear35A]

I am very happy with the 18# RSB flywheel and the clutch and pressure plate I got there as well. The little buzz at ~2300rpm is only noticeable in coast down and is even then almost nothing. I did not do any balancing, and it is smooth as a Lexus from idle to redline. I'm in Atlanta area too...Covington. Let's get together and compare 968 notes.

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[flash]

while you may have either gotten lucky, or aren't sensitive enough to feel it, you frequently won't feel the vibrations due to imbalance. they are very often too high in the harmonics, but can easily ruin things nonetheless, especially on the track.



remember that this car has balance shafts to deal with harmonics. those are carefully calculated to compensate for rotating mass. toss any of that mass out of balance, and things will not work like they should.



p.s. - i'm not taking any shots at pete or rs barn or the flywheel, but i know who actually makes that flywheel for rs barn, and even they tell you to balance it. i had that very conversation with them myself when it was still in the prototype stage. i have one of them in my car now, and i like it. however, it was out of balance 7 grams, and the pressure plate was out 11 (maybe the other way around. i'm forgetting now). this would definitely have messed things up.



this happens all the time though with all of the flywheel brands for just about any kind of car. it's a very real industry problem. the problem is that if a vendor tells a customer they have to balance the flywheel, which could then mean that the car has to sit on the rack another day, it may mean the loss of a sale of that flywheel. consequently they either downplay it or don't mention it at all. when it then goes bad, they almost never pay for the R&R or damage, often blaming it on other things.



don't roll the dice. always always always balance a single mass flywheel. it's only $50 and can save you a world of hurt.

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[hryden]

Thanks for all the excellent information. I think a single mass flywheel will be in order. Just out of curiosity, how reliable / durable are the single mass flywheels compared to the stock <acronym title='dual mass flywheel'>DMF</acronym>? The stock clutch and flywheel I had in the car have held up really well over several years of track duty, so I just want to get a feel for how the single mass flywheels might impact that.



Flash - what does balancing the flywheel entail and how does one get that done? I have not run across that before. Also, I read some earlier post mentioning that an S2 balancer should be added if using the Fidanza flywheel. Is this something I would need to be concerned with if I go with the Fidanza?



Lear35a - Thanks for your feedback on the RSBarn clutch and flywheel. Do you track your car at all? If so, maybe we can hook up at an event.

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[flash]

when properly installed, i have not heard of either of the above mentioned flywheels failing.



balancing is a simple process that many machine shops can do. basically they spin the mass, determine where the issue is, and then either drill to remove or weld to add weight in the right spot



i added the S2 balancer to mitigate some of the rattle. it smoothed things out, but in a race car i would likely not have done it.



i tracked the car a few times, but i don't personally feel that the 968 is a car for track. i think it's just too big and heavy, and that there are a lot better cars for track. i've driven smaller and lighter cars, and gone a lot faster, so i'm a bit spoiled there, and would never be happy dragging the 968 around a track. many people disagree with me on that though, but then again, they race lawnmowers too, so who am i to judge about what's right or wrong for the track?

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[Lear35A]

Over the years I did a lot of racing, SCCA and PCA Club Racing, and kind of burned myself out on that. My INTENTION is to keep my 968 as strictly a street car. However I can certainly drive it to a track like RA to assist, observe and socialize. <img src="/forum/images/smilies/968/biggrin.png" class="smilie" alt="" />



I put an S2 pulley on my engine when I rebuilt it using the RSB clutch & flywheel components. I have no idea if it makes any difference.

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[flash]

i'd bet that smoothed things out a bit. it did on mine. i was running without it at first.



the thing about dampeners and such is that in doing their job, they rob you of power. any energy absorbed by the dampener is energy not transmitted to the wheels.



that's another reason balancing is important. it allows for every bit of power to get to where it is supposed to, and not just be absorbed.



another benefit from balancing, at least in other cars, is that the redline can increase by as much as 500rpm, due to less resistance.

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[hryden]

Thanks for the information on balancing. I'll need to find a place here that does it.



I have to say I really enjoy the 968 on the track. That's not to say that I wouldn't love to have more power and less weight, but I really like the way it handles.

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[hryden]

My original intention was to keep it as a street car. After totaling my 911 at RA, I got the 968 as a street toy. Several years later, I got talked into taking the 968 out for a DE, and was amazed at how much fun the car was out of the box on the track (and how much I enjoyed it). Next thing I know, the interior is stripped, roll cage installed, seats and harnesses are installed, etc. and I am going to as many track events I can. <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />

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[Cloud9...68]

"I got the 968 as a street toy. Several years later, I got talked into taking the 968 out for a DE, and was amazed at how much fun the car was out of the box on the track (and how much I enjoyed it). Next thing I know, the interior is stripped, roll cage installed, seats and harnesses are installed, etc. and I am going to as many track events I can. <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />"



Glad to see I'm not the only one with this affliction. "We ought to have jackets made..."

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[DaveN]

The S2 pulley made a noticeable difference with my light weight flywheel. Took away that edge where you can stall the car if you don't rev it high enough in first gear.

The S2 pulley made a noticeable difference with my light weight flywheel. Took away that edge where you can stall the car if you don't rev it high enough in first gear.

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[Lear35A]

that's why I said I got burned out. I kept taking perfectly good street cars and little by little turning them into something worthless except for the track. I want a jacket...

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[flash]

lol - yeah - i think i need to get on that

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[Cloud9...68]

I take a medium-to-large. Navy or forest green.

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[Dubai944]

On my supercharged 968 engine I have used a Spec aluminum flywheel (13.5lbs I think) and Spec Stage 2 clutch for three race seasons now with zero problems. Nice light pedal, but very positive engagement and no slip. I replaced the clutch plate this year during an engine rebuild, but the old one was still in reasonably good condition despite two years of standing race starts and general hard driving and is now a spare. It would be ok to live with on the street if the car was mostly a track car. Don't know how it compares to others as I have never used anything else, but seems good to me <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />



When I first installed and started racing the 968 engine, the oil pickup tube sheared at the block flange and I broke a succession of alternator belt tensioners. I was advised by Racers Edge not to race the 968 engine without the S2 damper due to vibration at high rpm and since installing it have had no further breakages, so I guess it does it's job.

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[Cloud9...68]

"When I first installed and started racing the 968 engine, the oil pickup tube sheared at the block flange and I broke a succession of alternator belt tensioners. I was advised by Racers Edge not to race the 968 engine without the S2 damper due to vibration at high rpm and since installing it have had no further breakages, so I guess it does it's job."



Hmmm... Interesting...

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[hryden]

Just wanted to provide an update in case it helps others. I finally got around to installing everything and getting the car back on the track over the weekend. I ended up with a stock Sachs clutch and pressure plate (964 version) and the Fidanza flywheel. While I was in there I also replaced the main seal, the fork bearings and the fork pin. The fork bearings were seized and had pitted the fork pin which explains the notchiness in the clutch that has been there since I bought the car.



The new clutch is now very smooth. I had the clutch and flywheel balanced per Flash's recommendation and the whole thing is smooth as can be. The seat of the pants index also seems to think the car pulls a little stonger with the lighter flywheel as well and I also found it much easier to match revs on down shifts. As far as the noise from the drivetrain, it is now pretty loud especially when accelerating in a high gear at low rpm's. It's not too bad on deceleration, but noticable as well. As my car is a track car, this isn't a big deal, but if it was a street car, it would probably be unbearable. I wouldn't suggest it for a street car. I have not have any issues with stalling the car however.



This wasn't too bad a job except for getting the rear main seal pressed in and the new flywheel onto the crankshaft. Those were a pain. Per Fidanza's suggestion after a couple of previous tries, I heated up the flywheel before installing and it popped right in place. Once on, the rest of the assembly went pretty quickly and smoothly. I would definitely recommend investing in the flywheel tool as it made things much easier. All in all, the job took me about 10hrs total and I could probably do it in about half that next time. The job was more intimidating to me than it really was to do.



I also thought about using the S2 harmonic balancer, but the correct one is apparently no longer available at all. Is running the lightweight flywheel without it something i should be concerned about as far as damaging the engine in the long run?

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[bombfactory]

Thanks for writing up your experience. I will do doing my clutch here shortly and definitely replacing the fork pin and bearings. Still debating the pros and cons of going to a lightweight flywheel or sticking with the stock one that's in there now.

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