There's one more thing that I forgot to mention that affects a clutch's ability to do it's job and that is the clutch plates diameter. The physics of a lever can best explain this. The longer the lever is from the fulcrum point the more work will be accomplished with a given pressure. In the case of the clutch, a larger diameter clutch plate can transmit more torque than a smaller diameter with the same given in friction area, spring pressures and so on.

So what to do about my slipping clutch? I still have the new set of clutch plates that I could use and hope for the best. Now really--do you think that would be a option for a World Class Land Speed Record Contender? No way.

First a new clutch was in order in spades. I needed a clutch that would meet the following criteria. It would have to be able to transmit 600 foot pounds of torque time and time again. This would give me a 100 pound of torque wiggle room. Next the clutch had to be serviceable in the allotted turn around time during a record run. The two fastest record holders at the moment are the E-Z Hook Streamliner and the Ack Attack Streamliner. Both do not use a tow up; they drive off the line under their own power, so Black Lightning will do the same. Tow ups will be eliminated as it's a safer way to go. The Vincent streamliner will go with the flow on this one. The clutch had to be designed to launch a 1900 pound missile pulling an over all gear ratio of 1.4 to one. Of course it will get underway in low gear which will lighten the load so to speak. The clutch plates had to be an off the shelf item, current in design, and readily available for spares.

The parameters were set in stone. Now all I had to do was do it! The clutch project took a month and a half to complete.

I've just finished building a three plate slider clutch that is attached to the HYVO chain drive gear, with 6 5/16 inch counter sunk cap crews. It has 3 1/2 inch hardened pins that take the blunt of the torque transfer from the engines to the jack shaft.

For those who don't know what a slider clutch is I'll try to explain. It's basically designed like any other plate type clutch as far as the clutching together of clutch plates, transmitting the torque from the prime mover, i.e. the engines crankshaft rotation to the jack shaft.

The clutch plates consist of four 1/4 inch thick steel plates and measure 7 1/2 inches in diameter. There are six 3/4 inch concave radius' outboard of the clutch plate which serve as very robust dogs which marry the disks to the clutch basket.

The three bonded clutch plates have an outside diameter of 6 1/4 inches. The bonded area is from that dimension to the inboard circumference, which is 4". There are 4 heat expansion slots incorporated into each plate. The clutch plates have been broached to 1 1/2 inches with 16 tooth spline. Again quite a robust unit to marry itself to the 1 1/2" jack shaft. Both the steel plates and the bonded plates are made in Switzerland. The bonding material was developed by the European Air Bus on their braking material for the plane. Very high tech and very expensive. One set of clutch plates cost $900.00 U.S. The characteristic of the bonding material is unique in that it's friction coefficient increases as the material gets hotter during it's sliding phase of operation.

The heart of a slider clutch is it's pressure plate assembly and the mechanics of it's operation. The plate is so designed so as to accept a steel pressure plate that has 6 threaded studs that protrude through floater holes in the main portion of the assembly. That assembly is attached to the six adjustable 3/4" stands. Springs go over the six studs. The opposing pressure that the springs provide are adjustable by nut adjustment. There are six slots in the main plate which accept six fingers. The fingers are in a radial configuration and have a 1/4 inch hardened pin which lies in a milled trough in the main plate.

There are 1/4 inch holes that are drilled in the outer portion of the fingers. these holes are mounting holes for weights which are nothing more than equal weight washers.

How the pressure plate works is simple enough. At speed the clutch will be spinning at 4000 rpm. The floater pressure plate is moved to it's engaging position by the fingers. The fingers have a ratio of 5 to 1 at its fulcrum point. The fingers are nothing more than levers which depend on centrifugal force, providing movement of the finger lever. The opposing force on the pressure plate that the fingers are moving is the spring pressure. Sounds pretty simple? Well it ain't.

I needed more information as to how to initially set up Black Lightning's home built clutch. The only thing to do was to go to the people who have been there and done that.

First I called my old drag racer buddy, Bonni Truett. Some of you may have heard of him, as hundreds, if not thousands of H.D.'s are using the "Truett and Osbourn" stroker crankshafts. Anyway the only useful information I got out of Bonni was that the air gap of the clutch plates, when collapsed tight by hand should be .030 to .040. Seems kinda tight, but a couple of other racers have confirmed the gap since.

Next I called the Ram Clutch people, who build these things at a cost of $3,800. A friend had told me that they had a lot of good data that I needed for my initial set up. I gave them the clutch plate dimensions, finger geometry, number of fingers, finger swept circumference, clutch speed at idle, clutch speed at speed, preferred start lock up speed, and preferred lock up speed. It was in a matter of not more than 60 seconds that I had my answer for initial set up. Take 1/4 inch out of the free length of the springs. Add 50 grams of weight to each of the six fingers.

They said this is what the clutch should do--the clutch will start to lock up at 1600 engine rpm, will totally lock up at 3,000 rpm, the clutch will have 2,900 pounds of pressure on the clutch plates at 6,500 engine rpm, and the clutch will transmit 850 foot pounds of torque.

Perfect! Perfect! Perfect!

Now that the clutch is finished and it looks like it's going to work, there are a couple of things more that I would like to say. As the salt attacks everything made of metal, all of the steel parts of the clutch will be cad plated, the aluminum parts will be anodised. As the clutch is now external, a moisture proof bag will be placed over it when laid up after the day's runs. The clutch weighs in at a whopping 28 pounds. This thing is a serious hunk that will be spinning at 4,000 rpm. Hence I've had it balanced. The clutch was balanced as a unit, except for the friction clutch plates. The three friction clutch plates were balanced separately.