How much is it worth to have a clutch that will not fail?

[T_C_D]

" If one single holds 441rwtq then twins should be fine for 600rwtq."

this is the complete opposite of the point you were trying to make about reducing surface area to increase hp holding in one of your other clutch threads. ( the thread talking about your puck clutch)

The discs are only 7.25" and have a steel plate between them.

[Shadow]

two discs are better then one.

[sideways7]

" If one single holds 441rwtq then twins should be fine for 600rwtq."

this is the complete opposite of the point you were trying to make about reducing surface area to increase hp holding in one of your other clutch threads. ( the thread talking about your puck clutch)

The discs are only 7.25" and have a steel plate between them.

are you trying to imply that this is less surface area then your single disc puck clutch?

[winfred]

i believe the meaning behind the puck clutch holding is less surface area with the same pressure plate providing greater PSI of clamping force

" If one single holds 441rwtq then twins should be fine for 600rwtq."

this is the complete opposite of the point you were trying to make about reducing surface area to increase hp holding in one of your other clutch threads. ( the thread talking about your puck clutch)

[Murfinator]

I changed my mind. I am going with twin organic discs. If one single holds 441rwtq then twins should be fine for 600rwtq.

This is the bahama E28 with the Paul Burke machined b34 head and custom cam? Are there dyno numbers or are you just guessing regarding the engine output? I'm interested because I'm building a similar setup and worried about my current Sachs Sport clutch/PP/TOB holding ~ 500 ft/lbs of torque.

[George]

I changed my mind. I am going with twin organic discs. If one single holds 441rwtq then twins should be fine for 600rwtq.

This is the bahama E28 with the Paul Burke machined b34 head and custom cam? Are there dyno numbers or are you just guessing regarding the engine output? I'm interested because I'm building a similar setup and worried about my current Sachs Sport clutch/PP/TOB holding ~ 500 ft/lbs of torque.

Mike, it aint going to hold.

[T_C_D]

" If one single holds 441rwtq then twins should be fine for 600rwtq."

this is the complete opposite of the point you were trying to make about reducing surface area to increase hp holding in one of your other clutch threads. ( the thread talking about your puck clutch)

The discs are only 7.25" and have a steel plate between them.

are you trying to imply that this is less surface area then your single disc puck clutch?

I am not implying that a 7.25" disc has less surface area than a 9.25" disc.

Maybe one of the engineers can explain how a small twin disc has more holding capacity than a single bigger disc.

[George]

I think its pretty obvious.

[T_C_D]

I think its pretty obvious.

Only to wicked smart people like you.

[Murfinator]

I changed my mind. I am going with twin organic discs. If one single holds 441rwtq then twins should be fine for 600rwtq.

This is the bahama E28 with the Paul Burke machined b34 head and custom cam? Are there dyno numbers or are you just guessing regarding the engine output? I'm interested because I'm building a similar setup and worried about my current Sachs Sport clutch/PP/TOB holding ~ 500 ft/lbs of torque.

Mike, it aint going to hold.

Thanks. Thus the interest in this thread. I need a clutch option which costs less than $2k, won't require a PhD in mechanical engineering and will hold at least 500 ft/lbs of torque.

Do I buy a Tilton twin disk and pay someone to custom machine a flywheel? I've performed an auto to manual conversion but will I need to fly George to Utah to get this contraption to work? I'd rather go with a more plug and play setup though I wouldn't mind seeing George again and will definitely need help with the MS tune...

[George]

I think its pretty obvious.

Only to wicked smart people like you.

smartass

[sideways7]

two discs equals more surface area, which equals more grip. the advantage of a multidisc is that you don't have to use a crazy pressure plate spring. ( which makes a heavy pedal) the other advantage is that you don't have to use a very aggressive friction material. this makes drivability much better. this is all because of the large increase in the surface area of the friction material areas. you have 4 friction sides on a twin disc all transfering the power. yes, most mutli discs are smaller in diameter. this has the added benefit of bringing the rotating weight inboards, closer to the rotating axis. increasing the engine response. the downfall of mutlidiscss is the noise of the floater plate rattling around when the clutch pedal is pushed to the floor.

think of driving a rwd car with all season tires and having traction issues. you don't want to switch to a sticky drag tire. nor do you want to drive around with 500lbs in your trunk. so, you have the option of going to wider tires to increase the surface area. this helps grip.

[Jeremy]

All of that doesn't change the fact that a puck clutch holds more power because of reduced surface area with the same pressure plate behind it.

They're two different methods of solving the same problem, each with their own unique strengths and drawbacks.

[90e34535i]

The surface area has nothing to do with the grip, only the temperature and longevity. Larger discs have more leverage, so will hold more torque with the same friction material and clamp load.

Each Disc adds that much more torque capacity. A twin disc of the same size and material will have roughly twice the torque rating. Thats why more smaller discs with lower M.O.I. will hold more torque than a single large disc. More discs also helps to make the clutch last longer(ie. 3 discs vs 2 discs of the same size+material).

I've been running a triple disc Tilton(OT-II metallic disc's), on a 12lb modified m10 flywheel(car has been down for a while now, but should be running again next week). I bumped the idle up slightly and it idles totally smooth.

I'm also using a Tilton hydraulic release bearing, clutch effort is very low, but engagement is Very short. It requires a clutch stop,so it isn't TOO difficult to drive, and i could never get it to slip.

I cant wait to hear how your Twin organic discs work Todd, sounds like it should be a pretty easy driving setup. I think you made the right choice going to a 5 speed.

[Jeremy]

The surface area has nothing to do with the grip, only the temperature and longevity.

Wrong.

[George]

Oh my gosh, I'm not sure if there is mis-communication or mis-understanding here but my head hurts because everyone seems to be talking about something different.


The only thing pucks do is raise the contact pressure (psi) on the surface of the disc (puck) but total friction stays the same.


A puck clutch is used because the difference in COF between the materials. A puck clutch should be tolerant of more heat.

It also weighs less. The MOI for the disc itself is reduced. Which makes perfect sense. Less weight at the end of the disc makes for significantly less MOI.

As for the torque that a disc can hold. It is dependent up several variables. Everyone is right and everyone is wrong. Surface area is a variable but only with regards to the integration of the inner and outer radius. It creates a larger torque arm with regard to the center of axis.

Now, multiple discs enter into the equation with rather simplicity. They operate on a parallel axis and the torque increases with the number of surface areas. This means more discs is simply a multiplier.

Another thing to consider is that COF is a variable within itself as heat and speed change. Which is why some materials do better than others in different situations.


Here is the derivation for calculating torque for a clutch:

Torque =
[(COF * Force of Pressure Plate * #of surfaces / 3)] * [(Do^3-Di^3) / (Do-Di)]

All of that doesn't change the fact that a puck clutch holds more power because of reduced surface area with the same pressure plate behind it.

That is not correct. Pressure on surface area means nothing. Think about it this way:

Take a block of metal. One side is longer than the other. The force required to overcome the coefficient of static friction is the same regardless of what side the block is laying on. This remains true even though the pressure on the small side is larger than the big side due to the smaller area. Friction doesn't "know" pressure. It only sees force and mu.

[Coldswede]

That was a GREAT post George. Have you ever considered becoming a Physics Professor?

Seriously.

[Murfinator]

Thanks George. Your response was very informative.

My answer to Todd's original question is: < $2k and installed with a minimum of modification of surrounding parts. Also, the pedal feel should be close to stock, tractable, >20k miles longevity with moderate to harsh use and it can't sound like a tin can in a clothes dryer when the clutch is engaged.
I'm already running a UUC adjustable pedal stop but don't want an on/off clutch with no slip at engagement. That's not tractable. It must also reliably hold at minimum ~700 ft/lbs torque.

What are my options?

[mooseheadm5]

To add to this:
There are 4 ways to increase the amount of torque a clutch can hold (for each example assume everything else is held constant.)

1) Increase the normal force. This involves increasing the magnitude of the force that the pressure plate applies to the clutch disc. All other things being equal, this makes for a heavier pedal. This is why the M5 clutch is heavier than the 535 clutch. The disc is essentially the same, but the pressure plate uses heavier springs so that it presses harder against the disc.

2) Increase lever arm. Use a larger diameter friction surface. If using the same surface area, the increased diameter gives a longer torque arm for the applied friction force.

3) Increase mu (coefficient of friction.) Unfortunately, the types of clutch disc materials that have higher mu often don't provide good pedal modulation. They are also harder on the flywheel.

4)Increase number of parallel friction surfaces. George covered that pretty well.

[mooseheadm5]

My answer to Todd's original question is: < $2k and installed with a minimum of modification of surrounding parts. Also, the pedal feel should be close to stock, tractable, >20k miles longevity with moderate to harsh use and it can't sound like a tin can in a clothes dryer when the clutch is engaged.
I'm already running a UUC adjustable pedal stop but don't want an on/off clutch with no slip at engagement. That's not tractable. It must also reliably hold at minimum ~700 ft/lbs torque.

What are my options?

Not many, honestly.

[T_C_D]

I knew George would come through!

I have a spare single disc clutch kit minus the disc in stock.

Maybe I'll buy a iron disc just to see what it is like.

[sideways7]

so, you guys are saying that keeping everything else the same, (friction material and pressure plate spring) a solid disc and a puck disc will hold the same power? and i'm not referring to any sort of slipping to pull out, involving heat spikes. just straight holding power under load.

one thing i'm interested in is what clutch masters says about their reasoning for some of this. not what we assume the reasoning is... what the actual manufacturer is stating. that organic disc that tcd had that was cut into a puck clutch. what did they say that their goal was? to hold more power, or be more resistant to heat during launches and better shift response?

getting back to the original point of this thread... (and i have to admit it may have gotten a little off track because of me and i apologize for that) i think that 1200 is a great price for a good twin disc setup, and will definitely considering putting one in my car. i mainly work with exedy twin discs. (exedy is the oem for most japanese stuff, and has their own performance line) they run 16-1800 and use a cerametallic friction material and have a pedal feel not too much stiffer than stock. they also have a very progressive engagement.

for drag racing, there is a ton of heat involved on the launch. that is what kills the clutches. more friction surfaces, help spread everything out and keep the heat down. carbon friction materials love heat, and actually don't like to be cold. the carbonetics actually has a warmup procedure in their instructions. if you are about ready to drive the car hard, they tell you to pull the ebrake, rev the car to 3k or so, and lightly engange the clutch to slip it a little to get heat in it. they are also very nice to drive on the street. i still say if drag racing is your goal... carbon or some sort of auto is the only way to go.

carbon brakes are the same way. let's use alms prototypes as an example since that is what i am familiar with. the drivers will actually lightly drag the brakes on long straights to get heat in them before coming to the next corner. also, switching to carbon brakes eliminated brake changes during the longer 10-12 hour races.

i still say if drag racing is your goal... carbon or some sort of auto is the only way to go.

as for the street... with a high horsepower car, that doesn't see many or any launches, organic or a mild cerametallic is great.

mark

[George]

so, you guys are saying that keeping everything else the same, (friction material and pressure plate spring) a solid disc and a puck disc will hold the same power?

As long as the contact surfaces of the disc are in the same location on each disc.


It should be noted that slipping the clutch is often desired (drag racing). In this situation, you want a clutch disc and material that can handle the heat build up of the slip. This is where a puck clutch makes great sense.

[90e34535i]

The surface area has nothing to do with the grip, only the temperature and longevity.

Wrong.

Notice I said surface AREA and not the location of the friction surface on the disc(which has been pointed out is why a larger disc can have a bigger lever arm or more leverage and hold more torque with the same material/coefficient of friction and pressure).

[M. Holtmeier]

Any updates on this?

I'm planning on replacing my clutch this spring and curious to know if I'm better off buying a complete setup or if scrounging parts will work.

[T_C_D]

Any updates on this?

I'm planning on replacing my clutch this spring and curious to know if I'm better off buying a complete setup or if scrounging parts will work.

tranny will be in next week but I still have to do all the 5 speed conversion stuff.

BTW, my Sweeney modified hurst/bmw shifter arrived today.

[cvillebimmer]

but I still have to do all the 5 speed conversion stuff.

Whatevs... Just an afternoon's work.

Really liking the e31 brakes BTW. Thanks!

[lito]

clutch net 4puck,sachs sports pressure plate..worked fine with me...601whp ,610lbft

[George]

I ordered my Segmented Kevlar clutch from Todd yesterday. Plan is to break it in N/A along with new motor on e34.

[TheGraye28]

Sorry to drag up a topic from the depths, but does anyone have a review of Todd's stage 2 kit? Is a stock flywheel okay to use or is it necessary to get a lightweight one? Any help would be greatly appreciated.