Part 1. THE REASON AND BEGINNINGS
Never let it be said that there had to be a reason to build a bike, but in this case there was. Our Bonneville Ducati project had stalled and the process of testing was very cumbersome both in the dyno room and in the real world.
The necessity for electronic fuel injection (EFI) made itself known during the World Finals at Bonneville in October of 2009. Two intake manifold explosions brought that fact home emphatically. After returning, I read an article about a supercharged Mustang that suffered from a similar malady. Moving the fuel being delivered to a point under the throttle blades and closer to the motor reduced the size of the air/fuel charge just hanging out in the intake tubes and plenum looking for something to do. This something can be an explosion caused by a lean backfire, hanging an intake valve or the ignition having an episode and usually results in a loud, distracting bang. Venturing into the introduction of EFI would require a considerable amount of both dyno and real-world testing time. To set the dyno up for testing the Bonneville chassis involves the installation of two extensions to the front wheel clamp that basically puts the front wheel against the wall of the dyno room. To assemble and tear down this adaptation is a two –hour process and doesn’t lend itself to smooth operation of the dyno for our paying customers. It also takes three or four people to maneuver the long bike into the room and not tear anything off the bike in the process. The previous real world testing of the long bike at Byron Dragway got a lot of strange looks and during a run down the track it was spinning the wheel at 600 feet and again going through the timing lights at the end of the quarter mile. The excessive wheelspin and the attending engine rpm are what I suspect contributed to the loss of a crankshaft. All in all not very productive.
The obvious solution was a chassis that could accommodate the motor, manifolding and horsepower that didn’t require the disassembly of the dyno and doubled as a platform that could yield some real world results at the dragstrip. Looking back into my reference area I didn’t see anyone who had ever built a ProGas type chassis for a Ducati (or any other dragstrip-only Ducati chassis for that matter). The group led by Wayne Patterson in Australia with a modified stock chassis was as close as you could get. That left us to take care of that problem ourselves.
The last three bike chassis had been built for Bonneville, so we needed to change back to a previous thought processes. While Bonneville has very little weight transfer to deal with, the dragstrip needs a chassis capable of loading the rear tire in a productive manner. We elected to go with a solid rear end and use the weight distribution and power delivery characteristics to achieve that weight transfer. Another factor to consider is the possible use of this chassis as the basis of a Ducati dragracing platform for sale in the future. Something I have wanted to do for quite some time was develop a platform from which a person or team could learn to run a nitromethane-powered bike. At this point in time the only way to do that is with a Harley or a Top Fueler. There really isn’t a stepping stone to these classes. I will give the turbo bikes their due. We started running a turbo Kawasaki in Top Fuel in 1982, but switched to supercharged nitro halfway through the season after hearing Elmer Trett’s bike at Columbus. The turbo did well for us, but nothing, and I mean nothing can compare to the sound, smell and sensory overload a nitro bike can give you. My ultimate goal is to have enough money and time to run nitro at Bonneville. A nitro rush lasting minutes, not seconds. We have purchased 55 gallons of the stuff to try and make that happen.
The trick to this program would be to build a chassis capable of running the turbo for testing and then be able to be converted to injected nitro once the turbo was sorted out. Component location and weights became critical. An eye towards light weight again was brought to bear and this is where the roadracing and Top Fuel Bike and Car experience comes into play.
It is at this point in time I feel it is appropriate to mention the passing of a true genius and master chassis builder, Jim Ditullio, also known as “Puppet”. He was based out of the Buffalo New York area and was the creator of chassis for Elmer Trett, Jim McClure, and Larry McBride among many. I never had the opportunity to meet the man personally, one the few regrets I have, but his innovative approach to solving problems with the use of moly tubing was unique and will be sorely missed. I truly would have liked to see his solution to the problems of the Ducati project. His work was beautiful and worked.
Looking at a horsepower level of the turbo to be in the 300 to 320hp range, a certain amount of stiffness in the rear of the chassis was called for. Figuring out the quality of track surface the bike was to run on was crucial to determining the crank height and distance out from the rear axle would work best. Too far out and the weight wouldn’t transfer, leading to smoking the tire. Too far back and/or too high and the bike would want to transfer too much weight initially and flip over backwards or crash onto the wheelie bar and unload the tire. The track we run at the most in recent years is Byron Dragway in Byron IL. Ron Leek, the owner, has a track that was the scene of four-wide dragraces long before Charlotte was a dream. It is where we tested our Top Fuel Bikes and when properly prepared, has a superb surface, traction-wise. An anticipated bike weight of 285 to 295 lbs and planning to run the 7 ½ x 17 Mickey Thompson slick would give a good launch without the extra learning curve a 10” wide tire would entail. I have seen bikes run low 7 second passes on this tire. This might get a few converts from the turbo Hayabusa crowd.
This being potentially a production prototype, an eye towards the rider not experienced in riding a longer wheelbase bike had to be considered. A relatively steep 30 degree rake angle was chosen as the bike would then be more “driveable” out of the gate, rather than the response of a 45 degree nose, which is a bit more cumbersome. It also keeps the visual appearance of the bike from tending towards the extreme, and a bit more in keeping with the “ProStreet” appearance in vogue today.
Determining the wheelbase involved a few checks in the rulebook to see what wheelbase required wheelie bars in which classes. A 76 inch wheelbase was arrived at for this reason. It was long enough to be stable, yet still fit on an unmodified dyno carriage. The addition of wheelie bars can still be accommodated with the right choice of rear end components. The responsiveness of that length chassis again will accommodate the newcomer to purpose-built dragbikes.
Crank distance from the rear axle, as I mentioned earlier, determines the dynamic weight transfer characteristics of the chassis. If I had built another twin cylinder dragbike within the last 15 years it might be easier to determine that location. The last twin cylinder dragbike we did was a B-Fuel Harley in 1985 that finished #5 in the country and set the speed record in the quarter mile that year. It was a high gear only iron head, carbureted Sportster. Not a lot of cross-over, but some of its desirable traits could be brought forward.
To reduce the violence of the launch a fairly long crank to rear axle distance was needed. Tire technology has improved and tunability of the low speed characteristics has likewise become more quantifiable. The data acquisition and adjustability of the modern engine management systems is incredible compared to that of ten years ago. This makes the launch more tunable, but you still have to have the basic physical weight transfer occur to allow the most effective application of power to the track. This is also a needed aspect of a roadracing chassis where “roll centers” and weight transfer is not only fore and aft, but side to side as well. Tuning the roadracing chassis is primarily done with suspension adjustments (one the initial weight bias is properly set) where the dragracing chassis is tuned with component location (including the rider) and the clutch (assuming the power is there).
The distance to the ground from the crank centerline is another consideration that is constrained by rules within the various sanctioning bodies. A safe rule of thumb is 2 ½ inches of ground clearance with the tire at 6 psi and the rider seated on the bike. (Bonneville requires 4 inches of clearance between the seat/tail section and the ground, but no specific clearance minimum ahead of that.) The theory is that a violent launch and a quick chop of the throttle or sudden braking or a possible off-track excursion should keep the oil pan and exhaust from hitting the ground. Mind you, I said in theory. With a bike using wheelie bars this is likely to be true, with a no-bar bike, much less so. Our concern at this time is the difference in sump depth encountered between the Ducati 999 standard and the 999 deep sump cases. This can be a difference of about four inches, which is considerable.
Using the crank location of the Bonneville bike as a start, the crank height was set a bit higher. With the Bonneville bike having a 98 inch wheelbase and a 162 link chain, a compromise was achieved to try and get the best balance of launch and traction (theoretically). The hope is that the deep sump cases we plan to use for the nitro part of this project won’t be too much of a challenge in the ground clearance area. The deep sump is desirable to reduce the oil dilution from the nitro by increasing crankcase capacity and reduce the possible oil pump starvation due to acceleration. It’s a bit of a guess because I can’t afford a set right now and need to eat a few more weeks of cold sandwich lunches before we can get a set in here.
Well, it finally comes to the do-it stage and the components and dimension definition parts are loaded onto the frame jig.
As you can see, even at this early stage there are things that get priority and need to miss and not interfere with other things. Much like the construction of a building, there are certain things that have to go certain places. It is a bit different in the construction of a motorcycle in that the beams (frame tubes) are important, but once the engine and rear wheel relationship is established the chain run is god. You can’t have a frame tube or suspension component in the way. There is no negotiating. Here the final gear ratios of the bike need to be determined along with the pitch of the chain. The gear ratios will determine the size of the sprockets. Generally you want to have at least 15 to 16 teeth on the countershaft on a bike making 200 plus horsepower. This helps assure you have enough teeth engaged to transfer the power safely, not relying on too few teeth to do the job. This is called sprocket wrap. We use a custom made 18 tooth sprocket on the Land Speed Ducati and a similar 16 tooth sprocket on the Drag Ducati project as shown here.
Another concern is the use of belt drives, whether it is for a supercharger, magneto/fuel pump, primary or final drive. If too few teeth are engaged, off the teeth come with at the least an embarrassing end and in other cases, disaster; when a primary belt fails and over-revs the motor or a supercharger belt fails and knocks off the mag belt thus introducing random ignition timing and subsequent destruction. Ask me how I know. A relatively large countershaft sprocket allows a bit of location flexibility in the instance of the cross bracing of an outboard support tube.
The rear sprocket’s number of teeth needs to be calculated to allow the projected mph to be attained. There are a number of gearing calculators on the web. One that is interesting is the RB Racing website. A certain flexibility in the number of teeth is needed to allow for a stronger or weaker power delivery than planned. Plus or minus four teeth is ideal, but with some bracing requirements may be difficult. The wider the tire and the more power the more bracing will be needed.
Chain whip is another factor easy to overlook. If you have ever stood next to a bike doing a burnout, you can see chain whip first hand. The chain will wrap around the front sprocket and form an “S” shape as it exits. When the power is reversed, the opposite occurs. A bit of extra room and/or an effective chain guard/guide will help with this. Most sanctions require a chain guard of some type. On the Land Speed bike we run at Bonneville I didn’t trust the longevity of an idler wheel and the 162 link chain whipped magnificently and considering there is a three mile distance at near 200mph, the chain’s survival was questioned. Putting enough tension in the chain to keep it from whipping would have pulled the bearings out of the transmission and rear hub, so a guide was used with a HDPE strip to slide the chain along. A similar piece can be used here. For drag racing we don’t generally use the plastic strip, but a hell of a racket can be set up if the chain takes a stretch and you have a bit of a bouncy shut-down area.
Yellow twine helps define the chain run and keep tubes from being inadvertently placed in an unworkable location. This photo shows tying up the twine around the front sprocket.
The front end of the jig is set up to accommodate the steering head of the chassis. We machine our steering heads in house out of 4130 Chrome Moly steel. Roller bearings of common cross reference size are used to allow the fitment of a wide number of fork assemblies.
The fork length and wheel/tire diameter are determined and as we have already decided on the rake, the plates are set up accordingly. The writing on the plates is for different projects and can occasionally be a nuisance, but necessary.
Now you step back and look at it and decide if it is what you really had in mind. You need to get 15 or 20 feet away to really get a proper perspective. That is one of the reasons I have never been able to do a chassis on the computer. You are restricted to a much too myopic view of the project and can’t visualize it as a whole. We are now viewing the piece with either pride or puzzlement the location of the other key components that need to be considered before a single piece of tubing is bent. Things like a fuel tank, seating position, ignition components, battery (all important in the EFI programs), intake and exhaust systems and bodywork. A little planning now can save huge amounts of grief and agony later on. You spend another hour or so and make a half dozen pencil drawings…..then go home. This allows you to let things percolate in your mind and at least delay the first mistake until tomorrow.
Next, we get to it.