300guy

ehall:

What would you recommend? Going with a Fidanza flywheel with a sprung clutch disk? Switch to S2 flywheel/clutch/torque tube? (can this be done and keep stock 968 DME?) knife-edge/lighten the crankshaft?

BTW - does anyone have the total weight of Flywheel/clutch/PP for the 968, 944turbo and 944S2? I think that this would be a better comparison than JUST compaing weights of the flywheel.

thingo

Personally I think going to the 951 set up is like stepping back in time, clutch changes are so much more sensible with the 968

ehall

I think you should ask Raj. He is INTIMATELY falmiliar with the 968. There are a good many others here as well. For all of the work, time and research raj put into his car, I doubt if there is anyone you'll find more qualified to help you move down the right path. I believe soloracer also has a 968 turbo, as well as some others who race NA 968's. Those are the guys who know best for your model.
As for lightening/knife edging the crank, I can't say that I'm a big fan of that. You guys have oil squirters to lubricate the bearings, but we 951 guys don't, from stock. For us it probably makes sense to atleast cross drill the crank, maybe run and additional sump etc., because we tend to spin the #2 bearings. The speculation(which I have yet to see anyone prove for a fact) is that the 951 has oil pickip problems due to foaming caused by the rotation of the crank through the oil. Therefore one of the schools of thought is that knife edging and crossdrilling + polishing will all help to reduce splashing and foaming. The other reasons for this are to get the engine to rev faster, thus reducing turbo lag. Knife edging etc is pretty damned expensive for the sake of a guess at a preventative measure.
Now if the object is to make the car rev more easily, and to increase BHP, then one could also lighten the fw and PP. To me that is not only a less expensive route, but also, unless done to the extreme, it seems quite safe.
Something to note, Jon Milledge doesn't knife edge/trick out cranks, and he's known as somewhat of a performance genius with these cars. Another note is that special tool has made some incredibly high hp/tq numbers with basically a stock 2.5 ltr bottom end with a lt wt FW/pp.
So contact Raj first. Then do a search to include the 951 board, and you will find quite a large amount of info and differing opinions on this subject. I would also pm every single 968 turbo owner on the board and seek out their advise. They have ALL been down this trail before. Good luck.
E

PCinDC

Has anyone used the Spec lightweight flywheel/clutch combination? I am spec'ing (pun intended) out the clutch pack I'll use for my 3.1L Turbo, the Spec setup looks good as it has high torque capabilities along with light weight. I don't care about noise generated as this is a track car. I run the 968 bellhousing and require the 60-2 ring gear of the 968 (or S2) for use with my EMS. The Fidanza is significantly less expensive than the spec. I'm debating the following configurations:
1) Spec lightweight flywheel, Spec Stage 3 Full Metallic clutch kit
2) Fidanza lightweight flywheel, spec stage 3 full metallic clutch pack
3) S2 lightened flywheel/clutch combination (is this compatible with the 968 bellhousing/driveshaft? Want to retain the easy clutch change abilities.)
4) Open to other recommendations

Also, is the clutch fork (and its pin) shared between the 944 and 968 or is there a specific 968 part? If so, anyone know where I can find one?

Thanks!

flash968

i would definitely use something that has a better disk than the stock one - i have the fidanza in my car with a 3200lb pressure plate, and i fragged the disk at the track - it's fine for street use, but for the track, it just isn't up to the job of both hard clamping from the heavier plate, and the increased speed in which it must do it, due to the lighter flywheel - i'm not pushing nearly the power that a turbo would and i am already finding the limits of the disk

i'm planning on having a better disk made in a few weeks

PCinDC

Thanks for the input. I have no intention of putting anything stock or near-stock in there. The Spec disk is rated for 600+ foot pounds which is why I planned on going that route. I believe I read that the spec pressure plate is rated at 3400 pounds, need to check on that. Any current (or former) Spec users out there?

RajDatta

We used a Spec clutch in the 16 valve conversion and went with a stage 3 initially. The setup seemed severe from effort stand point so we went down to a stage 2. Do remember that, this is for a street only car.
As far as configurations, its always best to go with one manufacturer. This way there is no finger pointing on what part works what doesn't. Spec makes nice products.
3) Will not work in a 968 bell housing. Too much gap to make up from not running a DMF.
The fork is different but the pin is the same.
Raj

whakiewes

I have never purchased a Spec product in my lifetime, but I have installed about a dozen of their products and raced on a few. They are serious about their clutches, but the torque numbers have been a bit inflated for some of the uses I have seen. First example was a mildly modified 93' RX7 (HKS Intake, M2 exhaust, M2 ECU, about 250-270whp). We installed a Spec Stg. 3 onto the stock flywheel, mainly because the clutch saw a lot of abuse in the car. Clutch was much more on/off than stock, but was still easily slippable. Gave a much more direct feel between the engine and transmission. Second car was a 325is, 1990 that we put an MPD racing flywheel and Spec stg. 2. Again the clutch felt more than up to the task and was a very good setup. Bad experiences have all been in high HP cars, or I guess high torque cars. First was a Mustang that was supercharged (claimed 500whp, and 500wtq), had the Spec stg. 4 which was rated to some 600ft/lbs of torque. I wasn't present at the install but I saw the disk when it was removed when the friction discs tore apart from the disc. Second was a high power M3 (about 490wtq) had the Spec Stg 3+ which is basically a stg 4 with the feel of a stg 3. Same thing happened, stredded the friction plates right off the of the disc. The good and the bad!

Definantly take Raj and other guys advice on the 968 flywheel. I have played around with a ton but never pulled the trigger on a single setup. My objections and observations were that for one I wanted to keep the stock 968 bell housing. Not that frequent clutch changes would be needed, but the 2-piece bell housing does make it MUCH nicer than removing the torque tube and tranny for a clutch change (4hrs vs. 10 ). Second was that I didn't really have the $1000 it takes to get a Spec setup or Fidanza setup and Spec clutch...etc... I looked into OEM parts. The reason the 951 and 968 flywheels are so different in weight is the original design. The dual-mass flywheel is literally about twice as thick as the single mass 951 flywheel. Factory 951 flywheels are in the 14-16lb range, 968 is 32lbs on my scale. $75 and a good machinest can make the 951/S2 flywheel about 9lbs, sometimes less. Furthermore the 951 has MANY more clutch options for cars with power. Basically the 951 flywheel is about 1.5" thick, where as the 968 flywheel is about 2.5-3" thick. Regardless of whether an aftermarket unit is dual mass or single, its still got to make up the room in order to mate up with the input shaft of the torque tube. Unfortunately there is no median between 951 and 968 without serious work. The motorsport style seems the best solution, but at last check 9M wanted some $800 for their flywheel.

A few notes when I was studying this subject - the 968 is going to feel more vibrations from external modifications (such as pullies and flywheels) because of the longer stroke. Also the 951/968 cranks are pretty long for 4-cylinders (4X104mm vs. 6X86 or so) so you will feel vibrations from that. These vibrations you feel are going on in your engine, which decreases the life span of rod and main bearings. On inline 6's its always been advised to not run a lightweight flywheel and pullies because they are the engines harmonic balancers and the engine freaks out with the less weight. After going through the process of knife edging a crank and building a 951 engine, there is little to no gain. I wouldn't touch it on a 968 rebuild unless the project was budgetless or you were in the search for ultimate power. An exotic knife edged crank from a mass standpoint would yield at most a 5hp gain for about $1000+ worth of work. The $600 knife edging is a joke. Just get the parts balanced and be happy.

I ended up just deciding the stick with the OEM setup until I need more pressure. A lot of work for little gain. I drove a 968 with a Fidanza unit and it felt peppier, but I got the same feeling from adding a chip. Now when I get bored I just put the stock chip back in for a couple days and then the Racer X for the next week...makes me happy again .

Wes

JivenJim

I ran the Lindsey Lightweight (~16lbs) flywheel and Spec Stage II Clutch for about a year on a otherwise stock 968 motor in lighter 924S body. Very Good combo. Stage III or maybe IV if you push 500 Turbo HP. Would get the whole engine rotating mass balanced with flywheel by machine shop. I had no high RPM Vibrations without balance on stock internals, but idle with solid motor mounts was pretty rough. I also found broken support bracket between Oil Pick tube and return tube. Could of led to broken Pickup in time. So Get it balanced

I'm currently rebuilding after low oil and blowby from Stock Crank and 7000 RPM's. I'm going Knife edged, Crank Scraper, Cross drilled and lightened. Spun #2 968 Bearing and Bent crank at the track is something that $1500 can save $4000 for those that play hard. (over kill precaution but worth IMO)

Oh yea.. You will stall sometimes coming out of First till you learn to shift again. Count on that. But the lower Drive Train loss makes Turbo 944 and 911's wonder what you got under there. I'd guess 15HP to the wheels, gain.

I may make a circuit to help the TBS to help correct throttle drive on lightened internals if I can't find something out there off the shelf. Wes.. any tips?

300guy

I've removed the flywheel/disk/pressure plate from both a 968 and a 944S2 and weighed the pieces. The scale is analog, and not very accurate, however - for reference:

(Flywheel+Disk+Pressuer Plate= Total)

968 29.5 + 1 + 9.5 = 40lbs

968 13.5 (Spec) + 1 + 9.5 = 24lbs
40% weight savings from stock 968

944S2 14 + 2.5 + 18.5 = 35lbs
12.5 % weight savings from stock 968

944S2 11 (Spec) + 2.5 + 18.5 = 32lbs
20 % weight savings from stock 968

So - the 944S2 setup is 5 lbs lighter. Unfortunately the S2 pressure plate is real heavy, and, a lightwieght 944 turbo pressure plate can not be used.

The downside of using the extremely lightweight 968 setup with Spec. flywheel is that the solid 968 disk must be used. For a street car, this is not usually recommended.

richard glickel.

Assuming that you intend on keeping the 968 drive train, I'd suggest you contact Pete at RS Barn and check on his progress with the lightweight flywheel he's made for the 968. I think Pete plans on selling those flywheels soon.

300guy

I'm leaning towards using the S2 setup, so that I can have a sprung clutch disk. I understand that 968s with single mass flywheels are tough to shift due to the solid clutch disk.

Is there a lightweight pressure plate for the 944S2?

RajDatta

Did you try reaching KEP, lots of 944 turbo owners have used their pressure plates and they are lightweight. They migth have something for 944 S2 as well. Try the turbo forum, they should be able to point you to the correct url.
Raj

flash968

not at all - mine is a breeze to shift - in fact, it is much easier than stock to match gear speeds - you do have to pay attention and be quick about it, but that's about it

the new flywheel from rs barn should be even better, requiring less timing of the shift, resulting in smoother shifts for most drivers

RajDatta

There are others who have developed copies of motorsports flywheels. I was looking at getting a batch made at one point and the price was going to be in the $500 range. Since then I have opted to not do this upgrade because it is more for track/race cars.
Raj