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3,499 Posts
Discussion Starter · #1 · (Edited)
The less torque your car has at low RPM and the heavier the car, the more it will need a heavy flywheel/clutch assembly to get launched without overuse of the START button.

The Hellcat has mounds of torque, so it is easy to launch with the stock clutch, or the units that add mass, such as the McLeod and RAM systems (not all of the McLeod and RAM systems do this) that add a heavy plate to the existing flywheel, then mount the clutch on that.

The tradeoff is that you have a heavier clutch to accelerate as you go through each gear.
Now, the clutch plates themselves are not terribly heavy, so an 80-pound clutch assembly will not necessarily cause more wear and tear on the synchros during shifting (especially powershifting, where the foot is kept down on the gas, and the clutch just rapidly brushed then sidestepped.) The synchros only have to deal with the mass of the input shaft and the clutch disks, unless you are kinda sloppy about clutch engagement.

However, as the clutch is re-engaged after completing your shift, whatever momentum it gained during the shift (if powershifting) is rapidly spent on a bit of extra acceleration, but then the whole thing has to be accelerated again through the next gear.
If you want to see a fairly direct demonstration of flywheel mass and how it affects an engine, watch this episode of Garage 54 in Novosibersk, Russia.

The amount of time it takes your flywheel to accelerate to redline from your last shift point RPM, if disengaged from transmission, is directly piled on any acceleration figures you may have.
You can see this effect as they pile on more and more flywheels on this car, and how long it takes at wide open throttle (WOT) to get the engine to rev up.

However, most people are not racing for money on the street, so daily drivability is more of an issue than judder-starting from a standing start is worth.

The better/stronger holding/longer lasting a clutch material is, the grabbier it is, usually, so it takes a delicate touch to get the car to pull away from an intersection without unnecessary juddering or stalling.

If you are truly fanatical about polar moment, you can go with an on/off switch-engagement Pro Stock clutch that is 6 inches in diameter or so. Zero people would recommend that, however, unless your LIFE depended on how fast you get down a quarter mile, in which case you would want to put a Liberty or Lenco trans behind it, also, for example.

One of the best things, one of the biggest favors, you can do for your transmission is just put a Barton shifter on it. Then it feels like a true double-H gate instead of just a "third gear could be here, but, then again, it may be first, who knows? that the stock shifter seems to be good for. (I know, I had my shifter try to put me in third even though I was ever-so-carefully and slowly trying to get it into fifth gear. I knew to watch out for that with this particular shifter, thank God.) I have also had it go into first when trying to downshift into third.

BTW, if you want to know how a transmission SHOULD feel, buy a first-generation RX7. Don't believe me? Try one. I don't even know if Ferraris with gated shifters shifted with that much confidence and precision. (having never driven one.)

Research results so far:
Single-disk, twin-disk and triple-disk found so far. I think someone makes a quad-disk, also, IIRC.

Means of attaching the disks: strap or stand. The strap is strongest when accelerating, and due to it being a strap, has to be designed quite strong to be able to take full torque in reverse (as in when one shifts into the wrong gear and suddenly the engine is rapidly accelerated by the rear wheels)

The stand type uses a variety of means that, in short, have a post of some sort fastened to the part that is rotated by the engine directly: flywheel or flywheel add-on and the clutch disk(s) bear on those stands to be forced to rotate.

Mantic's clutches use stands with fairly long through-bolts run through them to hold them in place, so the through-bolts are actually in single shear, supporting the entire force of the clutch's attempt to not rotate with the flywheel as pressure is applied.

The brands that have the housing for the pressure plate bolting directly to an often-raised surface that is integral to the flywheel that are also stand-type have a sturdier, in engineering terms, situation where the long bolts holding the stands in place are in FAR stronger double-shear mounting, as far as the load placed on them by the floaters goes,as they are supported where they screw into the flywheel, and they are also supported at the head end where they pass through the pressure plate housing, because the pressure plate is held in place by being bolted directly to the flywheel or flywheel add-on.

By definition, all the bolts that attach ANYTHING to the flywheel itself are mounted in single shear, such as the bolts fastening the pressure plate assembly or any accessories to locate the floaters, etc.


Single shear (top of picture.) The load appied to the fastener is trying to "tip over" the fastener in addition to pulling on it perpendicular to the fastener's axis of rotation.

Double shear (bottom of picture) does not apply any lever-type force to the threads of the fastener, as the load is linear perpendicular to the fastener axis, and the fastener is securely held above and below the load.

A bolt that is one inch long in single shear, where the load placed on it is actually touching the opposite-direction shear object, namely, the flywheel, for example, is FAR sturdier than a bolt that is three inches long that is holding a pressure plate that far off of the flywheel, so the pressure plates that bolt directly to the flywheel or some other large, multi-bolt-fastened accessory, such as the RAM, with its arc-shaped pieces that bolt to the flywheel upon which they bolt their pressure plate, are sturdier, in engineering terms.

Engineering textbooks may be fascinating, but real-world experience by people who have to deal with clutches daily will tell you a more complete story about the positive or negative properties of a given brand/system/configuration of a clutch.

Centerforce has a unique setup where one of their dual clutch disks has a toothed basket that drives the second clutch from the first disk, instead of the second clutch disk being driven by the transmission splines directly. Centerforce also has weights on their diaphragm spring that increase clamp load as RPMs increase, claiming that this assists in high horsepower capability with lighter pedal effort. The Centerforce has a pressure plate that has small stands on which it mounts, but with straps on it.

UPDATE; Talked to Centerforce about their Dyad clutch. The Dyad is constructed as follows, in spite of what the web site says:
Ceramic or organic material, whichever you choose
Billet steel flywheel
NODULAR IRON floater, not cast.
NODULAR IRON ring onto which the pressure plate bolts.
I think they chose nodular iron (he emphasized that it is not cast) because it has a relatively low coefficient of thermal expansion, and thus, being the part that is sandwiched between two clutch disks, and therefore the one place that heat is most likely to build up, it will experience the least warpage of all materials they tested.

Also, the floater has non-radial sets of holes drilled in it like a Porsche racing brake rotor.

Evidently, multi-disk setups rattle or something when disengaged, my guess being that that is due to engine torsional vibrations acting on the different pieces in the assembly.

If I had it to do, I would go with a pressure plate housing that bolts directly to the flywheel, aka the way the stock clutch does, and the way some aftermarket clutches do, so the pressure plate is not, in effect, a hut placed on (admittedly sturdy) stilts, as I trust double-shear (in the case of stands being used to hold things in place in a multi-disk scenario) far more than I trust single shear, as do all engineers.

One anecdote I read from a stand-style clutch user was his friends wondered what was screwed up on his car from the noise emanating from his clutch.

Brands found so far:
McLeod (has a very wide range of offerings, both in organic and ceramic facings)
RAM (interesting in that their ceramic disks are offered for the Hellcat only with one sprung and one unsprung disk that is not directly tied to the sprung disk.)
Centerforce: has stand mounts, kind of, with ceramic, organic, or sintered iron offerings for the facings. Unique clutch disk has a sprung disk with a mating gear-tooth-type piece that ties it to the second disk, which does not bear on the input shaft itself, so ALL spring action is done by the springs in the one clutch disk.

Bad Boyzz Garage (BBG) with their "Monster" triple-plate clutch, they also have a dual-plate.

The Bad Boyzz Garage clutch mounts the pressure plate on stands, so, single shear stress on the bolts again with this brand. The floater(s) bear on the round dowels surrounding the bolts that secure the pressure plate.

Mantic, all are stand-style, dual and triple-plate, comes in a nice aluminum box/briefcase/whatever with a replacement TO bearing included
ACT has two models, I think.
Dunno if this all-carbon clutch will fit the Hellcat:
Carolina Clutch offers a strangely similar model specifically for the Hellcat:

MANTIC: Like other brands that offer a pressure plate that is mounted on stands/bolts in single shear (they may be just getting the same stuff and rebranding it) the Mantic has no direct connection between the pressure plate and flywheel.

Here is a picture of the components, including the pillars that the bolts go through:

SPEC: looks similar to the Mantic, but it is NOT the same. Pressure plate bolts directly to the flywheel, and the floater bears directly on the pressure plate housing, not on sleeves over bolts mounted in single shear. The bolts are, of course in single shear, strictly speaking, but the base of the integrated pillar/pressure plate through which they mount is FAR wider than the little pillars included with the Mantic.

Notice how the Spec (Hellcat version) bolts directly to the flywheel:

Of course, there are a variety of exotic, not-necessarily-streetable offerings with sintered iron facings for on/off switch engagement specifically made for racing.

RAM and McLeod have a setup where a thick additional flywheel face is bolted to the stock (or aftermarket) flywheel, then everything bolts to that. If smooth street driving is your thing, then this system will work pretty well, I think, because it adds a substantial amount of mass to the driven package, which will aid in getting moving without chatter.

If low polar moment is your thing, there are aluminum flywheels available from various sources, but make sure your flywheel will match whatever clutch you get, and if the setup is lighter than stock, either upgrade to a 2.98:1 first gear ratio from Rockland or be prepared to feather the clutch a bit more on starts from a standstill.

If anyone wants to add more information, I can update this first post to include it, such as additional clutch makers.

No clutches offered for the Hellcat by:
(Pity, as I had a nice aluminum pressure plate/flywheel from them on one car, and it felt no different than stock, except for faster acceleration.)

RAM: They need to edit their site. I found other email addresses that don't get bounced, and I notified them that they have that page that directs potential customers to the bad email address.

Mail Delivery Subsystem
11:30 PM (1 minute ago)
to me

Message blocked
Your message to [email protected] has been blocked. See technical details below for more information.
The response from the remote server was:
550 5.4.1 Recipient address rejected: Access denied. AS(201806281) []

I tried a different email from a different email provider on a different continent, and lo and behold: also rejected!

Clutch setup needs to be different, and even a different throwout bearing needs to be used with multi-disk clutches:

Mopar, of course.
Rockland Standard Gear: offers a variety of solutions, including lower ratios in first four gears, home of the famous Tranzilla.

RPM Transmissions: there one standout offering is cryogenically treating transmission internals, which evidently brings a higher level of toughness without either longevity or adding brittleness.

Their "Stage Seven" rebuild:
Anyone else want to chime in with other makers/rebuilders? I can add them to this first post.

Challenger SRT Hellcat
816 Posts
There have been several Rockland Gear Transmission failures that I know of that were running aftermarket high performance triple disc clutches, they were also highly modified 900+ HP cars.
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3,499 Posts
Discussion Starter · #3 ·
Well isn't that interesting.

Curious what were the circumstances and which gear cars were in when failure occured, if there is a pattern.

Premium Member
Challenger SRT Hellcat
345 Posts
Ya, RPS makes the clutches for Nth Moto
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3,499 Posts
Discussion Starter · #5 · (Edited)
Since only four images per post, here is an update with the unique Centerforce dual-disk system where only one disk has springs, BUT, the second disk ties directly onto that disk, thus concentrating all spring load to the six springs on the first disk. (unless there are six more on the back side of the thick first disk hub assembly.)

Challenger SRT Hellcat
816 Posts
I still have a slightly used Bad Boyz Triple Plate that I bought on the forum and did not install yet. I still want to get transmission with upgraded internals and different gear ratios and a scatter shield.
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