I'm posting the following from the American Vincent Owners NG. I found it most interesting & I know many here will too.
I'd get a coffee first, it's long and involved ;o))
regards,
Kim Siddorn.
The Land Speed Record Black Lightning's traction - i.e the rear tire's ability to make contact with the salt - was improved quite a bit by
*gearing* the two engines together. Now there might be those who say, "What in the world is Mad Max talking about here? This guy is certainly bonkers, and his handle fits. This is a ludicrous statement. There is no way gearing the two engines together will improve traction over chaining them together." Then there are the more astute on jtan that have already figured out where I'm going on this one.First it will be necessary to explain what was going on with the old chain driven way of doing things pertaining to the coupling of the two Vincent engines. The front engine had to have a minimum of 10 degrees lead on the rear engine. This was the only way that you could keep the chain from disintegrating and parting ways. That is, the two front cylinders were firing at approximately the same time, and of course likewise with the two rear cylinders of the two engines. As the chain stretched, the 10 degrees lead would grow 10,11,12,13, and so on until it was deemed necessary to replace the chain, which put it back to the original lead of 10 degrees. Then the process would start all over again. The second thing that's important to understand is what is referred to as power impulse duration. The power impulse duration is when the expanding gases (which is the ignited fuel in the cylinder) expand, forcing the piston down on the power stroke. The force which creates torque on the crankshaft is not a constant due to the fuel's burning characteristic, (starting with a small flame and growing at a faster rate during the burn cycle of the fuel.) As the mechanics of a crankshaft are varying a great deal during the power stroke, meaning during 180 degrees of crankshaft rotation, the leverage goes from zero at top to it's max at 90 degrees, back to zero at 180 degrees bottom. Therefore the power impulse duration has a definite fingerprint, and there is a definite spike in the torque to the rear wheel, as the two engines with a chain coupling them together and the front leading the rear by 10 or more degrees. This increased the power impulse duration of the two engines by overlapping the two engines power impulse fingerprints. By gearing the engines together the 10 to 15 degree overlap of the two engines power pulses were eliminated. Both engines will be fired at the same time, hence decreasing the duration of the power pulse fingerprint. Now to the meat of what goes on at the rear wheel concerning the traction it will provide to move the liner from point "A" to point "B". For the sake of eliminating the math involved we will not concern ourselves with overall gear ratios. For this exercise the ratio will be
1 to 1. In other words when the crankshaft turns over one time, the rear wheel does the same. As the engines are four stroke and there are two cylinders firing at the same time with their fixed power impulse duration, the rear wheel would receive one power impulse per revolution shorter in duration. Well--not quite. We have a "V" twin, where the cylinders lie 50 degrees apart, but for this exercise we'll forget the 50 degree thing. As the driving torque to the rear wheel occurs during the duration of the power impulse from the burning fuel, this is the only time the rear wheel feels unconstant torque force. The duration of this unconstant force is fixed in the volumetric efficiency of the engines mechanical pieces employed. After the torque force from the burning fuel takes place, the rear wheel then is receiving a kinetic force from all of the gear trains mass, as well as the crankshafts mass. This kinetic force is not violent in nature, but rather smooth in it's deliverance to the salt through the wheel and tire. The tire has a friction coefficient which at speed will be a constant, other than the liner becoming lighter due to the fuel being burned at a high rate. When the power impulse occurs the spike from that impulse causes the tire to break traction from the salt surface. The duration of this spike in torque determines how much the wheel is turning faster than the liner is actually going. The shorter the torque duration the faster the wheels speed is reduced, as once the wheel or tire breaks traction, the easier the tire accelerates and a longer power impulse duration really gets the tire spinning. To further prove my point one would only have to think about it a bit. All racers who have been there know that this is not hogwash, but a fact. If you were to take a dirt track sprint car and put a V8 engine with a given torque and horsepower proven on a dyno and take a four cylinder engine with the same torque and horsepower proven on the dyno, the four cylinder would have better lap times than the V8 in the same car due to less impulses providing better traction. Once you start the wheel spinning the further you can get the power impulses apart, the better it is and traction increases. This will be a pretty good advantage that Black Lightning will have over the multi-cylinder machines that are in the race to be the Worlds Fastest Motorcycle--The Easy Hook, The Ack Attack and the Dennis Manning Special Max.