Street manners are excellent.

Before I bought, I called Spec and talked with a guy there for a while. I told him what my car is (stock LT1), how I intend to use it (mostly street driving, with no dragstrip duty -- it's a ragtop, after all, and if I'm gonna drag race a Corvette it'll be the LT4 coupe, not the ragtop), and what sort of behavior I wanted (as little gear rattle as possible, and engagement that was near-stock).

He recommended their Stage 2 clutch (Kevlar sprung-hub disc), and of course, the extra-weight steel SMF, which I'd already decided I wanted, hoping to minimize gear rattle after deep-sixing the DMF.

The engagement is smooth and predictable -- not grabby at all. Zero chatter when starting out from a dead stop in first gear. I've noticed a tiny bit of chatter a couple of times when starting off in reverse, but the thing's still in the break-in period, so that may vanish as the clutch seats, and it's superficial, so I won't sweat it even if it still occasionally shows up in reverse.

The day after I got the car back together, I drove it to my club's annual Corvette weekend event in Ocean City, MD. That event includes a parade down the length of the boardwalk (around 35 blocks), and the clutch was nice and smooth in that stop-and-go action. A grabby clutch would have been a real handful in a long parade such as that, but the behavior of this clutch was totally civilized. The rotational inertia of this heavyweight DMF probably contributes to the smooth and easy launches.

Summary: Superb street manners. Zero gear rattle in my car ('94, blue-tag ZF, running Amsoil 5W-30 synchromesh full-synthetic gear oil). I can't say what'll happen in other cars with black-tag ZFs, cammed engines, different gear oil, etc, but I'm thrilled to not have the can-o'-rocks clatter in mine. I really didn't want to hear that in this street-only car. And, hopefully, a nice long clutch life with this Kevlar disc. But only time will tell about that.

Live well,

SJW

 

Am I introuble because I ordered the stage 1? I knew nothing about the kevlar. Owell I guess. New is better than what I had in there

 

I hope you'll end up as satisfied as I am so far. I feel very good about the choice I made. If it continues to perform well, and proves to be durable, it'll turn out to be a winner, and I'm optimistic that'll turn out to be the case. I was impressed with the quality of the parts after examining them closely, and I'm not easily impressed. I judged their engineering and manufacturing to be excellent, based upon a careful inspection and the limited amount of driving I've done so far.

Live well,

SJW

 

Nothing wrong with an organic clutch. Ft. Wayne Clutch recommended them (to me) over Kevlar.

 

The Stage 1 will probably be just fine for you, if you don't drag race or abuse the clutch. I would expect that the Stage 1 should hold up at least as well as a stock setup, and probably better. If you think you might rather have the Stage 2 kit, call them quickly and see if they've already shipped your order out. If not, they would probably let you change the order.

I went with the Stage 2, hoping that it'll give me longer life than the Stage 1 would have, but without compromising street manners such as would probably have been the case with a full-on drag racing clutch. The Stage 2 sounded like a good blend of smooth engagement and ruggedness, so I went with it.

I'm sorry to have not gotten to your PM in time to give you part numbers before you placed your order. I've been extremely busy the past coupla days, and have had only a limited amount of time to spend here on the forum.

Best of luck with it, whichever one you end up with. Take your time and do the install carefully, and it should work out just fine.

Live well,

SJW

 

Being extra-cautious about it, I had the new SMF match-balanced against my old DMF, and it turned out that the new SMF was almost perfectly matched to the DMF straight out of the box. I wanted the peace-of-mind that came with knowing the balance was right before I bolted everything in. Doing a clutch swap on a ZF C4 on a Kwiklift is not a job for the faint of heart, and I did not want to do the job twice because of a balance problem that could have been prevented, so I had it checked before I installed everything.

Based upon the fact that mine checked out nearly perfect, I would think that you should be okay if you bolt everything in as-received. Do take the time to thoroughly clean the clutch surfaces on the flywheel and pressure plate before you install, of course, to remove any preservative or traces of machine oil, etc.

You can get your old and new flywheels match-balanced just to be certain, if that suits you. But you'll probably be okay if you decide to not bother with that.

Live well,

SJW

 

Here's the toasted stock clutch that I removed from the car (note the absence of springs in the hub of the disc):



And here's the spank-new, sprung-hub disc from Spec, sitting atop the pressure plate, with the heavyweight billet steel SMF sitting to the left:



Note the six springs in the hub of the new clutch disc.

Live well,

SJW

 

Sorry to bring back an old thread,
I'm going to be buying the SPEC extra mass flywheel and stage 2 clutch shortly, but I am wondering is the new flywheel much heavier or the same weight as the original DMFW? Carolina clutch claims their SMFW weighs the same as the stock unit, however they do not come matched balanced, rather they are zero balanced requiring the installer to match balance prior to assembly.

If it is heavier have those who run them notice a decrease in performance?

Thanks

 

I have a 92 coupe with 93 Engine and ZF 6 speed. Ithas been converted to s single mass Fly wheel and I have excessive gear clatter in neutral that goes away when engaged. whats the fix as I'm new at this

 

Checking in:

supercharged 93 with a spec stage III+ sprung hub clutch (spec 2 kevlar blew up on me on the highway a few years ago) AND lightweight louis fidanza aluminum flywheel.

Very happy.

Im not sure why all these people think the 'heavy' SMF is the way to go. Theres not a lot of noise on my setup. Slight knock at neutral with clutch out. Only some minor rattle if you lug the car up a hill in-too-high-of-a-gear

I think the key is to have a sprung hub clutch. I also have the blue tag zf which might also help. Itd be interesting to see which people complain about noise with SMF - blue tag or black tag ZF owners.

The dual mass is a lot of weight to be slinging around in there thats just a waste. You must overcome that rotational inertia every time you accelerate. Hot rod did an article one time of drag racing a heavy mass flywheel against a lightweight flywheel and found that any launch gains were eclipsed by top end gains on the car with the lightweight flywheel. The lightweight flywheel car was the faster car.

and im sure louis fidanza would agree...

 

From what I can gather -

DM Flywheel weight - 39lbs
Spec Billet Steel SM - 30lbs

I am not sure that the listed weight for the flywheel is with the extra mass option or not.

 

Sprung hub isn't the key, but it's a big part of the equation. I'd previously thought it might be a blue vs black tag issue, but that theory didn't hold water when I posted it a year/two back.

Since gear noise is less for blue tags anyway, you'd think they'd be quieter...and maybe they are in this regard too. After all, perception varies from owner-to-owner. But, I also think tolerances of the specific transmissions fit in here somewhere.

 

Heavier units engage a little easier with less slipping of the clutch..the stored energy is great when hitting the next gear.


know that a flywheel can be good but can chatter if you get grease or oil on your disk. Done that one before.

Youll like the Spec billet, its a nice piece. In fact imo nicer appearing anyway than the billet CF one imo. Both work well.

 

I don't have a scale here at the house, so I didn't weigh the DMF, or the new Spec extra-weight SMF before I installed it. Spec should be able to tell you the difference in weight between the two.

The Spec unit is bolt-in. There's no need to have it match-balanced. I did, just to be sure, and the balance came up nearly perfect on it, so I would have been just fine if I'd have skipped the trip to the balance shop. That's a definite benefit, IMHO.

Flywheel mass, like everything else in engineering, involves compromises and trade-offs. The question you need to ask yourself, is "How do I intend to use the vehicle after I install these parts?"

If the answer is "It's a race car, that will see mostly/only track duty", you'll likely be happier with a low-mass FW, as the lower mass equates to reduced rotational inertia, and thus slightly faster crankshaft acceleration.

If the answer is "It's a street car, that will mostly be driven normally, but with occasional spirited runs through the gears, you'll likely be happier with the extra-weight FW, as its higher mass equates to easier launches (you'll need to work the throttle much less to get the clutch engaged without stalling the engine), and it will probably reduce - and maybe eliminate - gear rattle in the ZF gearbox.

A lightweight FW will gain you a tenth or two at the dragstrip, if that's of great importance to you. The seat-of-the-pants acceleration experience, on a street driven car, probably won't be much different. And it'll probably leave you with some pretty obnoxious gear rattle.

The heavyweight FW, while perhaps costing you a tenth or two on a timeslip, will be much more liveable on the street, because of the easier engagement characteristics, and the reduction or absence of gear rattle.

I'm very pleased with the Spec extra-weight steel SMF and Stage 2 clutch kit in my stock '94 LT1 ragtop car. It's a street-only car (if I were going to the track, I'd take my LT4 coupe), and the combination has proved to be very civilized for street use. Clutch engagement is silky-smooth and confident, with easy launches and little throttle action required, and I was fortunate to end up with zero gear rattle at idle.

The amount of gear rattle you'll get with a SMF seems to be driven by numerous factors, including:

1. Mass of SMF
2. Angle of helical gear cut in gearbox (blue tag vs black tag, with blue tag helping to reduce gear rattle a bit)
3. Idle characteristics of engine (idle speed, presence/absence of lope from aggressive camshaft, etc)
4. Solid vs sprung-hub clutch disk (go with sprung-hub when you ditch the DMF in a street-driven car)

Gear lubricant may also play a small role, although I can say that I've had no gear rattle at idle in my '94 with either Amsoil Synchromesh lube, or the Castrol/BMW lube that ZF Doc recommends, so I'm doubtful it makes much difference WRT gear rattle.

Live well,

SJW

 

Presuming your car now has a lightweight SMF (?), you might not be able to do a lot about the gear rattle without swapping in a heavier FW. I'd suggest you try raising the idle speed a bit, and see what that does for you (be aware that this isn't properly done using an idle stop screw, as was true of the old carbureted engines -- follow the procedure in the factory service manual).

Live well,

SJW

 

 

Thank you for your reply!!! I guess I'll Live with the gear clatter till the end of the cruising season as long as the gear clatter isn't an indication of more serious problems. Thanks again!!!!!

 

Thanks!!!!

 

I thank you for your input and response.....Thanks again

 

My son and I are installing a Spec stage 2, and extra weight smf fly wheel this weekend. Stock 94, street use car once or twice a year we do a driving session on a track. Would someone please comment on the gear lubricant issue. Is there a recommendation to change the gear lube to address and noise issue? Thanks.