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#2449125 - 02/09/18 12:37 PM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: moparpoolman]
weedburner Offline


Registered: 10/21/14
Posts: 45
Loc: Washington
Originally Posted By DGS
Originally Posted By weedburner
Here's some very general calculated torque capacities per 1000lbs of clamp pressure for typical "10.5" clutch discs (actually around 10.375" dia od friction material)...

organic- 180ftlbs
dual friction- 276ftlbs
ceramic- 293ftlbs
iron- 289ftlbs

From those numbers if a 440 made 600ftlbs, here's the minimum amount of clamp required to hold the torque for various friction materials...

organic- 3334 lbs
dual friction- 2175 lbs
ceramic- 2048 lbs
iron- 2076 lbs

With the typical adjustable you are trying to slip as much as you can off the line without slipping too much in high gear. An organic disc is going to limit what you can do as it loses cof as it gains temperature. Ceramic is a pretty much the same compound as a ceramic brake pad, heat doesn't really change cof much. Iron does exactly what you want as it gains cof as you work thru the gears, which widens your tuning window.

From the above you can also see why ceramic has such a bad reputation for being like an "off/on switch". They are typically paired with a pressure plate suited to hold an organic disc, when they should be paired with a pressure more like that for an iron disc.



ok, so if I would do all clutch slipping with the pedal the "ideal" clutch setup would be a pressure plate that has just enough base pressure to not slip at idle and added counterweight pressure that follows the torque curve throughout the rpm range.
Well, since the added counterweight pressure usually can't follow the torque curve perfectly (centrifugal pressure increases exponentially whereas the torque curve usually has more of a logarithmic shape) you start with a higher base pressure and add less centrifugal pressure, correct?

In my case I have a McLeod B&B/Long PP (360951) with 2400lbs base pressure and counterweights. If I would use an organic disc I need roughly 1000 lbs of centrifugal pressure at the rpm I hit 600 ft/lbs of torque (let's say at 4000rpm) for the clutch not to slip (2400 base + 1000 = 3400 pressure). At 6000rpm the centrifugal pressure is more than double that at 4000rpm which is not really necessary as the torque increase between both points is only a few ft/lbs.
Would I be better off if I lower the base pressure and centrifugal assist (less or no counterweights) and run a disc with a higher friction coefficient than an organic disc?

This only takes into account going through the rpm range without shifting (where you don't want your clutch to slip).
When shifting you want some slippage though - otherwise shifts are too violent (at least for a street car). So is a dual friction disc the solution in a street car? It would have some slippage when shifting but a much higher cof (less base and centrifugal pressure needed).


Using base/counterweights is actually a pretty crude way to dial in a clutch.

The calculated pressure to hold a certain torque doesn't include the additional pressure necessary to cause rpm fallback after a wot shift. Fallback is the indicator of inertia energy being released from the rotating assy, which adds torque to the input shaft. The amount of additional clamp pressure over that required to hold the engine's torque is what determines the rate of inertia energy release from the rotating assy during fallback. Not enough additional clamp, rpm won't fallback fast enough and the clutch will slip too long and burn up. Too much additional clamp and it will fallback too fast, creating a much more concentrated release of inertia energy from the rotating assy which shows up as a huge torque spike to the input shaft.

Here's some shortcomings of using counterweights to control clutch slip-

...Staging rpm is limited, as too much rpm causes the counterweight in the clutch to hit the tires too hard. This reduces the amount of energy you can effectively store in the rotating assy on the starting line.

...While counterweight can allow for some slip after shifts, which effectively raises fallback rpm to increase net hp, it wastes more of that fallback energy release than it needs to. Just look at a graph of a base/counterweight run to see the evidence. First you will see the rpm trace fall straight down after the shift, which indicates a quick/intense release of inertia energy from the rotating assy...so intense that it shows up as a wheelspeed spike on the driveshaft rpm trace. When rpm gets pulled down far enough, the fallback part of the engine rpm trace begins to transition into a backwards "J" shape. This lower curved part of the backwards "J" is where the effective clutch slip occurs that actually raises hp. The upper vertical part of the backwards "J" was the clutch not slipping enough, causing fallback energy to be wasted in a blip of tire spin.

Theoretically the rotating assy is just an energy storage device- it soaks up energy when accelerated, then gives that same energy back as it slows down. If that give/take were actually averaging out, there shouldn't be much difference overall in a heavy vs lite flywheel/clutch comparison. But there is a difference that I believe shows up on the time slip for two basic reasons...

1- lower launch rpm compared to the trap rpm. Basically if you were to launch a car at 6000 and trap at 8000, the engine will be burdened with creating enough additional energy during the run to make up that overall 2000rpm difference. Keep in mind the exponential effect that comes with rpm, it takes 16x more energy to accelerate that rotating assy from 6000 to 8000 as it did to accelerate it from 0 to 2000. In this case a lighter rotating assy is an advantage because it will absorb less energy while making up that 2000rpm difference between launch and trap.

2- less energy wasted in the post shift wheelspeed spike. The problem is the return of energy after the typical adjustable clutch shift is so intense that it instantly knocks the tires loose, instead of being applied over time to usefully accelerate the entire car. Then the engine has to make up that wasted energy as it accelerates the rotating assy back up to the next shift point. Because a lighter rotating assy releases less energy as it loses rpm, that also reduces the amount of energy wasted as wheelspin after the shift.

Because the ClutchTamer is time based and does not rely on counterweight to manage clutch slip, it gives you the ability to launch at 8k without killing the tires, which effectively makes it possible to pack more energy into the rotating assy prior to launch. The softer hit after a clutched shift then converts fallback energy that would otherwise be wasted in a wheelspeed spike into productive energy. These two things work to restore a more balanced give/take relationship of energy stored in the rotating assy, greatly reducing or eliminating the advantage of a lightweight clutch/flywheel assy. This allows using a heavier clutch assy with more thermal mass with little penalty, which in turn allows one to further exploit clutch slip to effectively raise the engine's average rpm and increase horsepower production even further.


Edited by weedburner (02/09/18 12:39 PM)

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#2449181 - 02/09/18 03:40 PM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: moparpoolman]
madscientist Offline


Registered: 09/17/14
Posts: 1953
Loc: Washington
Stock, Super Stock, Comp and Pro Stock must be ignorant.

They all use CW and lever ratios to tune their clutches. Except for a few classes which are mandated to run an OE clutch.


You should probably slide by the Elite Motorsports trailer this weekend and let them know your way of clutch tuning is better. And cheaper. And more tune able.
_________________________
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston

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#2449416 - 02/10/18 02:19 AM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: moparpoolman]
weedburner Offline


Registered: 10/21/14
Posts: 45
Loc: Washington
Make a sweep thru the nhra stock, super stock, and comp records for stick cars, let me know how they stack up against the 1320/mph=et efficiency formula. You will find that they have around the same reletive efficiency as the Coyote Stock guys. Some come in a little under the formula, some come in a little above, my point is that even the trick clutches and clutchless transmissions that are used in Super Stock are no more efficient at converting mph to et than the single disc diaphragm and clutch assist setup the Coyote Stock guys use.

Pro Stock pretty much has to use centrifugal assist, pretty tough to get enough clamp without it.

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#2449540 - 02/10/18 12:04 PM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: weedburner]
cudaman1969 Offline
master

Registered: 01/25/04
Posts: 4167
Loc: fredericksburg,va
Originally Posted By weedburner
Make a sweep thru the nhra stock, super stock, and comp records for stick cars, let me know how they stack up against the 1320/mph=et efficiency formula. You will find that they have around the same reletive efficiency as the Coyote Stock guys. Some come in a little under the formula, some come in a little above, my point is that even the trick clutches and clutchless transmissions that are used in Super Stock are no more efficient at converting mph to et than the single disc diaphragm and clutch assist setup the Coyote Stock guys use.

Pro Stock pretty much has to use centrifugal assist, pretty tough to get enough clamp without it.

Well you talked me into doing as you say since I already have a new diaphragm plate and a disc that has different material on either side. My nephew worked at perfection clutch in SC and set this up for me. He said they made all the clutches for the hipo company's.

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#2450437 - 02/11/18 09:41 PM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: weedburner]
moparpoolman Offline
enthusiast

Registered: 11/27/06
Posts: 319
Loc: NE
Is there a site that would have the clamping force numbers of various clutches?? or where could I find that info?

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#2450453 - 02/11/18 10:15 PM Re: Adjustable or Non-adjustable Clutch Advise Needed [Re: moparpoolman]
madscientist Offline


Registered: 09/17/14
Posts: 1953
Loc: Washington
Originally Posted By moparpoolman
Is there a site that would have the clamping force numbers of various clutches?? or where could I find that info?


Used to be a chart on blackmagicclutches.com
_________________________
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston

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