Driveline thread, very important info on clutch design

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 low polar moment, which is how referred to by most as "rotational inertia," you can go with the seemingly 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. If I was running a Lenco, I would consider just using a tight torque converter with a lockup I could switch on and off.

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.)


ANYWAY, ONWARD TO CLUTCHES AND TRANSMISSIONS:
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.

 

IMPORTANT NOTE:
A CLUTCH THAT FLOATS ITS PRESSURE PLATE OFF OF THE FLYWHEEL ON PILLARS OR STANDS THAT ARE NOT ONE PIECE WITH THE PRESSURE PLATE HAS A POTENTIAL TO LOOSEN, RATTLE, AND FAIL. IT IS ONE REASON CLUTCHES THAT ARE DESIGNED TO LAST TENS OF THOUSANDS OF MILES WITH NO SERVICE OR REPLACEMENT HAVE A PRESSURE PLATE THAT IS ONE STAMPED PIECE OF STEEL OR A ONE-PIECE BILLET 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's bellhousing but I do not see why not:
https://www.nthmoto.com/viper-quad-carbon-clutch

Carolina Clutch offers a strangely similar model specifically for the Hellcat:
https://www.carolinaclutch.com/product/rps-billet-carbon-hellcat-triple-disc-clutch-kit

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:

This type of clutch is hyper-not-recommended by me, period. This style is famous for loosening and rattling LOUDLY.

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 long bolts mounted in single shear upon which the pressure plate can act with torque far away from the flywheel and cause rocking/loosening.


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:
ZOOM
None offered either by LuK (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 supposedly has some clutches for the Hemi and TR6060 transmission.

 

Some Transmissions:

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

Vendors:

Mopar, of course. Or, at least, they USED to sell them.

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

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

"Level six and seven" rebuilds on this page:
https://rpmtransmissions.com/product-category/dodge+challenger+2020/

Found this will looking for TR6060's for sale on the 'net.

TR6060/6070 | Calimer Performance Transmissions

www.calimertransmissions.com

 

SPEC:
I notice that like many, only one of the clutch disks is sprung. This is interesting to me.


SPEC Super Twin Clutch Kit SS-Trim: Dodge Challenger Hellcat SRT - SD80SST-H
SPEC Super Twin Clutch Kit SS-Trim: Dodge Challenger Hellcat SRT - SD80SST-H. **** BEFORE Ordering, please check your application using the SPEC Catalog.
www.lmperformance.com




The pressure plate is mounted SOLIDLY to the flywheel itself, which, to me is a VERY important feature in engineering terms, as it is not tottering atop little stands that no manufacturers use if they are making a clutch for longevity.

It is not a strap-driven assembly, so there IS a potential for some rattle, IN THEORY, but there is NO potential for the strap to buckle (pun) under reverse torque. So far, this is the one I like the most in terms of its structural design of the ones I've seen below 5,000 dollars.

Evidently someone was looking at the stresses when it was designed, as the bolts to hold it to the flywheel are NOT centered in the stands, but placed where they will have the most positive effect in reducing the rocking effect of a single-shear bolt placement.

Also, the price:1769 bux.
SD80SST-O-2 is the one that will fit most people's SRT's, etc. and will do just great. All organic lining, but they have other options available that cost more.

https://specclutch.com/applications...r_year=2016&type=14845&product_type=supertwin

The available aluminum flywheel has a steel friction face, and you can specify which flywheel you want.
They also sell a throwout bearing.

https://specclutch.com/products/#multi-disc-clutches


I wonder at the longevity of the friction material. There is not a lot of thickness between finished surface and the beginning of the rivets, and to me, that is a concern, as it limits the useful friction material to around half of the thickness on the puck.

I would not be above ordering clutch friction disks from elsewhere to put in this clutch if they had no rivets, as it would aid in longevity, in my view. I have never been a fan of riveted friction material, but it does tend to stay put and not slide off.

But, as a counterpoint, our brake pads have material that stays put, and they do not use rivets; it ain't rocket science.

 

Forgive me if I've missed the point of this thread but what comes to mind is that I can't imagine a Dodge warranty is going to provide an owner with any relief if they determine breakage has occurred as a result of 'powershifting' the standard transmission. And it will happen (makes for a short evening). And have you heard of something called a 'scatter shield'?

 

For those who want The Last Word in clutch capability and feel:
https://www.nthmoto.com/viper-quad-carbon-clutch

For those who are tempted to blow a whole briefcase of money on one of the stupid, fragile, weak, oh, yes, stupid, carbon fiber or aluminum driveshafts, but really do prefer a driveshaft that does not end up as a pile of carbon powder or a pretzel, then the bone-stock Redeye driveshaft comes HIGHLY recommended.



The driveshaft is such a tiny diameter, it has an absolutely minimal impact on polar moment overall of the rotating assembly, and it is FAR stronger in the WAY STRONGER, MORE RELIABLE AND ONE HECK OF A LOT CHEAPER sense than the fluffy carbon fiber garbage and aluminum future pretzels sold by the guys who make money every time one of their weak Fluffmaster 5000 driveshafts breaks.

(No warranty, of course, but what good would it do? Are they going to dispatch a Hawker Harrier with a mechanic to come install it for you by the side of the road or racetrack?


I conjecture that the reason they use CV joints instead of U-joints for the driveshafts is that U-joints require at least 1.5 degrees of angle on each end to work properly. If not, the bearing needles just get pounded flat and quit working properly.

Ironically, aluminum is a great damper of impact/vibrations, but carbon fiber is not, so the theory of "unchecked harmonic torsional vibration" for the carbon fiber driveshaft doesn't seem to apply in the case of the aluminum shaft.

Also, the last video showing the truck doing a burnout, which one would think is not exactly a highly-stresssed part of a driveshaft's life and the driveshaft pitching right out of the side from underneath the truck is not what I would call an advertisement for the piece's quality.

Now, the Demons that have exploded their pumpkins right at launch but have NOT pretzeled their driveshafts indicate that the driveshaft is definitely not the weakest link.

 

Speaking of "weakest links," here is one way to avoid the weakest link being the rear axle area, a Ford 9" (one of the best strength-to-weight ratios of all replaceable rear axles) center section you can drop into your still-IRS rearend:

https://driveshaftshop.com/product/...conversion-kit-includes-axles-and-driveshaft/

Also: https://www.moserengineering.com/2009-Newer-Challenger-M9-Rear-Solid-Axle-Sub-Frame-Kit.item

Or just go all Ham on it and put in a solid axle: