Nitro 101

The Ducati fueler project has finally come to a point where we can go out and attempt to embarrass ourselves in public.   

With the mechanical fuel injection’s arrival we can move forward with the development.

A more detailed discussion of the theatrics will ensue, but after finish-machining of the components, installation and plumbing, the bike was ready to test in the driveway.

(this is actually a burnout from earlier in the summer when it was still a turbo system but it still looks cool)

After surviving a somewhat inept burnout attempt, a full throttle squirt spun the tire for fourty feet and it didn’t blow up.  That qualified it for the next phase, the dyno.

Once in the dyno room it was a bit of a project to get things situated as the startup requires the shot of flammables to be added and the fuel turned on at the same time.  Once the motor was warmed up on alcohol, this was done and once the bike settled into its idle, Nick ran through the gears quickly and watching the exhaust gas temps not exceed 1100 degrees F, we vacated the room as quickly as possible as the exhaust fans weren’t up to the task of exhausting and your eyes and nose let you know.

Well it survived the second phase where it didn’t blow up, so the entry for Bonneville was mailed out that afternoon.    This is where the story picks up on the Bonneville blog. 

After returning from a frustrated attempt at running on the salt (rained out), it was decided to test the bike at Byron Dragway, and once again, if it didn’t blow up, off toValdosta Georgia and the Manufacturer’s Cup Race there.  In unexplored territory with a not too commonly used fuel capable of  tremendous power gains this is always a possibility kept in the back of your mind, especially using all stock parts.   

The next thing that would make the platform more user friendly would be the addition of the slider clutch.  This allows the rider to simply turn the throttle and leave, taking the application of the clutch and the vaguaries of starting line surface traction out of the equation to a great extent.  

Now Ducatis are known for their slipper clutches.  These are back-torque limiting units that keep the rear wheel from locking up on hard deceleration due to engine braking.  They slip the plates just a little bit.  You can do the same thing manually but it takes a lot of experience and concentration to do it in a productive manner. 

A slider clutch, on the other hand, slips the plates on acceleration.  The amount of slip and rpms the bikes launches at are adjustable to a great extent.  This allows the tailoring of the first 100 to 150 feet of the launch to be tailored to the conditions of the track and the motor, thus allowing the best 60 ft. times, otherwise known as “short times”.  Getting the show moving is paramount in a race of acceleration such as this.  Improvements in short times usually can be parlayed into a multiplier down track.  Say you are able to knock .10 seconds off the short time.  This often will show itself as a .14 to .16 second improvement at the end of the quarter mile.  There are amazing 60 foot times to be had, often in the 1.05 second range for motorcycles and for a Top Fuel car .886 seconds is not uncommon. 

Now I was looking around and discovered, to my non-amazement, that nobody makes a slider clutch for a Ducati.  We have two slipper clutches in stock at the shop, but as I mentioned before, they work in the wrong direction.  Now the hunt was on for what it took to make one.

A slider clutch is centrifugally activated.  That is to say that there are a series of arms that swing out in a small arc.  Weight on the ends of the arms located in the outermost piece, called the “hat”, adds force to the tips which in turn bear down on the pressure plate.  The pressure plate in turn squeezes the clutch discs together and, voila!, the bike (or car) moves forward.  To keep the arms from squeezing the plates together too soon, a series of springs are used to hold the pressure plate away from the clutch plates.  The strength and adjustment of the preload of these springs determines at what rpm the clutch closes (or engages) at.  There is a balancing act involved where the strength of the springs and the amount of weight has to be reckoned with.  The spring strength has to be subtracted from the arm weight force and hopefully leaves enough pressure to keep the clutch closed up at the higher rpms.  This is where there were huge gains made in the 1980s by Dale Armstrong using a second set of arms that, when released, closed the clutch up tighter and made for big speed gains.  Unfortunately we don’t have the sophistication in this initial configuration and need to listen to the motor and look at the clutch plates.

Once the basic and seemingly simple understanding of  the clutch function is grasped, the next step is to see what may be available to adapt to use rather than reinvent the wheel.  Looking around, MTC Engineering had a hat assembly  available and once we had ordered a sample fiber plate from each model they offered it was determined that the Kawasaki ZX-12 was the most likely suspect.  Ordering the hat assembly was simple.  Now came the challenge of fitting it to a Ducati outer basket and clearancing the inner parts so as to not hit.  The allowance for travel of the pressure plate and its attending whirly bits was imperative so as to not wind up with a handful of aluminum shavings after the first activation.  A trip to Houston in the van allowed a fair amount of time to think about and draw the approximations of parts.  Once back in the real world, however, things were different. 

Making the hat mounting ring was a bit of a process as it required cutting it from a sheet of chromoly.  Lacking the sophisticated devices to do this meant it had to be done at night so as to not piss off everyone in the shop with the noise and smell as it had to be done with an abrasive because the plasma cutter wasn’t up to the task, and conventional flame cutting would make for tears when it came time for machining. 

Eventually the parts were made to play well together and it was time to test.  A used Ducati 900SS on the showroom floor was chosen as the likely candidate and everything just bolted in.  Amazing.  On startup I realized that if nothing else, we had made a clutch that was louder than the Ducati stock dry clutch.  It was pretty scary to listen to at first at idle, but once the rpms were picked up and the arms started to bear on the pressure plate, things quieted down a bit.    Backing it off the lift and starting it up was a bit of a thrill as I had no idea what may happen.  Was the pressure plate too close to the inner hub, allowing the shavings and an instant one-piece clutch?  Was it too far away and wouldn’t engage?  The pack clearance was within specifications, but the primary ratio was unaccounted for in the speed at which the hat would turn and thus its actuation characteristics.  Clicking it into what I assumed was first gear a light application of throttle gave a twitch of movement.  Out to the driveway we go. 

Pointed towards a relatively open area, applying the throttle gave a satisfying forward movement.  Let off and it slowed down.  Good, especially the slowing down part.  More spirited application and away we went.  Now for the burnout.  Roll into some water in third gear and apply the throttle.  Sounded a bit weak and I looked back and the only smoke was coming from the clutch.  Nick pointed out that you needed to snap the driveline to keep from killing the plates.  He rides John Gilchrist’s Kawasaki H2 dragbike in Super Eliminator and has a lot of laps with a slider clutch.  Following his advice worked the charm and smoke rolled out at a satisfying rate from the rear tire.  Snap the throttle off and it quit rolling.  Good again.  Now to take it inside and take it apart.  Either it would go right into the fueler or into the trash.  Everything looked good so into the fueler it went.


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