Engines, but not stationary

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))
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
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
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
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
Reply to
Kim Siddorn
Loading thread data ...

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.