Bonneville, Anyone?
BONNEVILLE, ANYONE?
GORDON H. JENNINGS
SIXTEEN YEARS AGO, the SCTA (Southern California Timing Association) hot rod club organized the first Bonneville National Speed Trials, and as a result of their enterprise, the Bonneville Salt Flats were opened to the average automobile enthusiast. A bit later, motorcyclists were invited to, come out and participate in the Speed Trials (under the aegis of the AMA) and for both car and bike enthusiasts, the Speed Trials have become an event of increasing interest and importance. We gave the Bonneville National Speed Trials a lot of attention last year, both as journalists and participants, and we have been getting letters from interested motorcyclists ever since. Most of the letters ask about classes, rules, and when it is all to happen in 1964, and the purpose of this article is to oblige all those requests. We will also outline some of the problems, from the standpoint of both riders and tuners, that are likely to be encountered on Utah's famous Salt Flats.
The AMA has set up a multitude of classes in which one may try for a record; the classification of a machine depending upon displacement, the degree of streamlining, the engine being used, and the frame. In most of these classes (there are 288) no record exists, and any two-way average speed will become a record. However, all of the fun lies in trying to go really fast (over 150 mph) or in breaking an existing record. And, of course, it is also enlightening, if not always entertaining, to bring out a "street stock" machine and find out how fast it will really run.
The basic displacement classes are as follows:
All of these figures are, obviously, upper limits. Actually, for Class C engines a .045" overbore is allowed even if it nudges the engine a bit over the limit. This provision makes it possible to "clean up" the bores a couple of times and allow running clearance for a 40-over piston without pushing the engine up into a higher displacement category. No such allowance is made for a Class A engine; the bore and stroke are measured, and the displacement must be within the stated limits for the class, period.
In addition to displacement, engines are grouped according to type, and by the extent of the modifications made to them. Class A engines can burn any fuel that you can get into the tank before it explodes, and the engine can be of any design so long as it was produced by a bona fide motorcycle manufacturer. Any and all modifications are permitted, such as converting to overhead camshafts, altering bore and stroke (which may put the engine in a higher or lower displacement class), or anything else as long as you start with a motorcycle manufacturer's engine — even if it is a special racing engine. Supercharging is permitted, but places the engine in Class AB (B meaning "Blower"). In previous years, any engine under 3000cc displacement qualified for Class A; unfortunately the motorcycle manufacturers who direct the policies of the AMA have decided that leaving Class A open for anything is bad business, so from now on we shall all be obliged to use one of their engines.
Class C engines must be a bit nearer stock. They must run on commercially available fuel of not over 100 octane, and at Bonneville you will be provided with good old Mobilgas. Supercharging is forbidden, and the engine must be nominally in the same condition as it was when it left the factory of its origin. Parts (other than the head, cylinder, and crankcase) may be replaced with special parts, but the replacements must closely resemble the original equipment. You can fit special cams and valves, and alter the ports in any manner whatever, and change the connecting rod length. The stroke must remain as stock, but modifications to the flywheel(s) are legal. You can use any size or type of carburetor, and fuel injection may be legal. We are not too certain on this point, as to the best of our knowledge no ruling has been made. We are fairly sure that the rest of the modifications are permitted, because that is what is being done at Bonneville. The rule book is of little or no help in this matter, because it is too indefinitely worded. In the end, you just have to accept the ruling of the AMA referee on the spot, and you may find yourself running a Class A engine when Class C was what you had in mind. The book says that you must run "the same basic engine design as approved" and that "the manufacturers (sic) crank cases, cylinder and cylinder head from approved models must be used," whatever all that really means.
There are a couple of special dispensa tions for under-250cc bikes running in Class C: five-speed transmissions are permitted (4-speeds only in Class C Heavyweights) and engines may be brought up to 250cc limit by boring or stroking, or both. You can also vary the bore and stroke of a 250cc ... engine, if you stay under the 250cc limit, provided that the new bore and stroke dimensions are registered with the AMA by the manufacturer or distributor of the bike in question.
The rules for frames and running gear at Bonneville are reasonably clear. Class C frames may have plates or struts added, in the interest of safety, and brackets or lugs may be removed or lightened. You can find out a bit more about this by consulting the AMA rule book: the rules for Class C road racing frames apply at Bonneville. Class A frames may be modified production type frames, or they may be entirely special construction.
Speed being the whole reason for going to Bonneville, you may want to employ streamlining. There are classes for partially streamlined bikes (Class PS) and for those having more or less complete streamlining (Class S). Partially Streamlined bikes must have the rider and front wheel entirely exposed when viewed from the side, and funny-business with transparent materials will not get you past this rule. Current road-racing bikes, with their abbreviated fairings, are good examples of Class PS machines. If the front wheel or rider is enclosed, the bike falls in Class S, even though a large part of the machine is left bare. Similarly, any streamlining at all, even "airfoil" fairings on the fork legs or a small cone in front of the steering head, will put a bike in Class PS.
The old speed-merchant's technique of riding stretched-out to reduce wind resistance is not permitted on bikes having a Class C frame. The foot pegs on a Class C frame cannot be higher or farther back than the rear axle, and the rider's feet must be on the pegs during a run. In Class A you can stretch out, but the frame must be extended back to hold pegs where the rider's feet will be — and his feet must be on the pegs while he is making a run. The purpose of this rule is to insure that the rider will have a secure perch, which is a good thing, as the salt is not nearly as smooth as most people fancy it to be. A rider prone on a bike, without the foot pegs, might suddenly find himself prone on the salt while still traveling at great speed — and that sort of thing will scuff one's leathers something awful.
Bikes at Bonneville are classified by displacement, engine, frame and streamlining. For example: a standard BSA 650 twin would be classified as C-C 650 (C frame, C engine, 650cc displacement). A Norton Manx road racing bike would be in Class PS-A-A 500 (Partially Streamlined — assuming it had a fairing), A frame, A engine, 500cc displacement. Add a supercharger to the above Norton and it would be classified as PS-A-AB 500. Within very broad limits, if you start with a manufactured motorcycle no matter what is done to it there will be a class for it at Bonneville.
Tuners who have acquired their training in racing other than at Bonneville (and that of course takes in all but a mere handful of tuners) will find the Salt Flats a strange and baffling place. As most people already know, the altitude there is about 4300 feet, and the air is warm and thin, so that engines simply do not develop as much power as they do down nearer sea-level. Also, most people have the idea that a Bonneville engine should be tuned for maximum power — even if it kills the engine's medium range torque. This is a dreadful mistake. To go really fast, you will have to pile on a lot of gear, and you may find that the engine won't pull the bike fast enough to get itself "up on the cam." Using a four-speed transmission, it is inevitable that the engine will drop a lot of rpm after each shift, and while at low speeds this will only make the engine slow to accelerate back up to peaking speed, the drop in rpm after shifting from 3rd to 4th can bring the engine far enough back down on its power curve so that wind drag will prevent it from climbing back up to its peak. What this all means is that an engine for Bonneville must, unless you are prepared to go to a five, six or seven speed gearbox, have a wide range of power — even if the peak output is limited slightly as a result.
Another point to remember is that overall gearing should be such that the engine goes just past its peaking speed as the bike reaches top speed. When this is done, the slight gusts of wind that slow the bike will have the effect of pushing the engine back up to its peaking speed, and that will tend to cancel the effect of the wind. Gearing so that engine and road speeds peak at the same point causes the engine to be pulled down from its peak by the gusts. Also, it is a practical impossibility to get the gearing exactly right, and your chances of getting a good twoway average are better with a slightly toohigh gear ratio.
Carburetion can also get a tuner into trouble. With the engine pulling such a tall gear, oyer such a distance, it is essential to be a bit over-rich at low and medium engine speeds. An engine that runs clean at all speeds is sure to be too lean at top speed, and if that happens several large holes will appear in the pistons as if by magic. Start rich with your jetting, and work back to a mixture that is correct at top speed. "Fuelers" are, of course, especially critical in this regard.
Do not fret too much over brakes. A lot of room is provided in which to stop after a run, and wind resistance will pull a bike down to below 100 mph very quickly without the aid of brakes. Traction is extremely limited, too, so we would advise that the front brake be disconnected. The action of the rear brake should be weakened to prevent the rider from inadvertently locking the rear wheel.
First-time Bonneville riders will find that the salt flats are a tougher ride than they could possibly imagine. The ride is tough because it is completely different from what one finds any place else. The water table lies just under the salt, so it is always wet, and the course gets progressively rougher and more rutted as Speed Week wears on. Those big, powerful cars churn up the surface, and if you happen to get into a groove carved by some eager hot-dog, it will carry you and your scooter along just like a streetcar track. Side winds, which may be present at the traps even when the air is calm at the starting line, can also provide some unexpected thrills for the rider.
Apart from making certain that his machine is in perfect condition, the rider's main concern should be that he does nothing sudden while riding. No tire known to man gets more than a light grip on the salt, and a rider can provoke wheelspin by a slam-bang shift, or even too much throttle at the wrong time. There will be a tendency for riders to hurry their shifts. Wind resistance slows the bike very quickly when the clutch is pulled in to make a shift, and when the engine tends to fall off the cam, the rider will try to shift rapidly so as to lose as few rpm as possible. If he coordinates clutch and throttle so the power does not come in with a bang as the clutch drops home everything will be fine. Too much enthusiasm and too little finesse will provoke a great blast of wheelspin — and traction, once lost, is not quickly recovered. This has been the direct cause of at least one rider's unloading at high speed.
A good rider will also help his tuner by judging his machine's acceleration so that it reaches top speed just before arriving at the traps. During record runs, you will find yourself running at full throttle for almost 3 miles continuously, and even at 150 mph the 1-mile stretch through the traps feels as though it will last forever. Anyone who has a shred of sensitivity for machines will cringe at the load and speed at which the engine is working. Thus, it is necessary to nurse the engine along as much as possible — consistent with hitting the start of the timed section at top speed, of course. Finally, at the end of each run, the rider should roll smoothly back on the throttle and bump the transmission into neutral, killing the ignition at the same time. This will enable the hard working tuner to get a valid plug reading, which he will need to set the mixture.
No special qualifications have been set forth for riders at Bonneville, but Earl Flanders, who is the AMA referee for the Speed Trials, tells us that every entry blank should be accompanied by a resume of the rider's competition experience. People who have no high-speed experience will not be permitted to ride. And, of course, as the speed potential of the machine increases, so do the experience requirements for the rider.
Every rider will be required to have a full suit of leathers, an AMA approved helmet and shatter-proof goggles. Also, bring your gloves and boots. Some riders (those who are much braver than bright) will think all the protective riding gear is a bit sissy, but the salt is hard and abrasive, and due to the action of the salt on flesh, "burns" acquired from sliding over it take a very long time to heal.
Other safety requirements are stem lock nuts and valve caps, which are needed because centrifugal force at high speeds will try to pull the valve stem out through the rim, and it can also unseat the valve, which will cause the tire to suddenly deflate. Fully enclosed streamliners must have some provision for getting a supply of fresh air in to the rider. The preferred method is to have the rider use an oxygen mask, with air coming in through a hose from an outside scoop. Also in streamliners, the rider must be separated from the engine and fuel supply by a firewall. The canopy must be provided with latches that can be operated from inside or outside, and there must be a roll bar, seat belt and shoulder harness. Those of you who may object to all this should bear in mind the fact that Earl Flanders is simply trying to keep you alive.
To enter the Bonneville Speed Trials you should obtain an entry blank from Earl Flanders, the AMA referee. Write to: the Flanders Company, 200 West Walnut St., Pasadena, California. Mr. Flanders will send you back an SCTA entry blank which, when signed, takes care of the legal formalities, and a supplementary form to be filled out with details about your motorcycle. Your entry forms, when returned, will have to be accompanied by $28, for the first entry, and if you plan to use different engines $20 must be paid for each additional engine. Post entries will cost you $40. These fees go to Bonneville Nationals, Inc., but the entry forms should be returned, with the fees, to Earl Flanders. He will forward the fees to Bonneville Nationals, Inc., where they are used to pay for insurance, timing equipment, etc.
One final note: if you are planning a really fast machine for Bonneville, first make sure that you will be able to obtain the necessary tires. You will not be allowed to run at high speeds on anything but high-speed tires, and these must be ordered in advance from either Dunlop or Avon, who may or may not decide to oblige. In any case, check this before building your machine. •
