Adding speed dimples have proven to create more power if you are using the blue power bands on your AV7 or AV10 Moby motors. If you have the correct torrification ratio when you drill your ringland ports, as they align to the speed dimples they will create a reduction in load on the crankshaft. When the crankshaft spins, the offset lobes carrying the journals set up harmonic vibrations in the cases and cylinders. These vibrations cause air to be sucked out of the combustions chambers, past the rings which act like one-way valves in much the same manner as the reed valve in a diaphragm pump. The air is then stored in the transfer ports which act as a energy reservoir and can hold tremendous pressure. Because there are at least two transfer ports and reservoirs this also provides and equalized balance to the engine. These ports are opened up when an engine is blueprinted and balanced and sometimes more are added for added boost.
Once the transfer ports are fully charged the engine will create a vacuum in the combustion chamber. The resulting vacuum causes the intake and exhaust ports to open (due to the pressure differential) allowing mixture to be drawn into the crankcase on the carb side, and spent combustion fumes on the exhaust side. The momentum of the inrushing gas pulls the pistons down from underneath, in what is known as the "intake stroke". The pulling effect is so strong that the piston needs to have a rod to hold it in the engine called a connecting rod. The connecting rod prevents the pistons from falling out of the cylinders and into the cases, or from hitting the combustion chamber sides. Turbo engine are usually equipped with more then one connecting rod because of the increase in piston vacuum.
After the chamber is full, the pressure differential holding open the ports is relieved, and the ports shut. The mixture begins to cool slightly, producing a reverse pressure gradient, owing to the large amount of air pumped into the crankcase. The reverse gradient along with the temperature differential allows the energy stored in the transfer port to transfer down the passage called the crankshaft. Along with the vibratory energy supplied by the crankshaft, the pistons begin to move back towards the tops of the cylinders in what is known as the "compression stroke". As the density of the cylinder gases increases, the air and gasoline molecules are forced together more and more.
Because they are already quite hot from spent gases which were taken in during the intake cycle, their kinetic energy is high, and many collisions occur. At a critical point, the air and gas molecules suddenly combine violently. The kinetic energy from tis violent collision is focussed in the magneto because of the spinning magnets attracting the electrons towards the spark plug. When the energy contained in the magneto becomes too great the points are made to open which work like a circuit breaker and cause a spark for combustion.
The "combustion" causes the mixture to burn off all of the gasoline in the mixture which creates a void as the fuel is depleated. The mixture starts to implode, and cool rapidly as the kinetic and thermal energy is absorbed. This makes the gas pressure drop, and the pistons are sucked strongly towards the top of the cylinders. The resulting unbalanced acceleration produces a driving force which is resonant with the vibration of the crankshaft, reinforcing its motion.
Because of the momentum imparted to the pistons during the implosion of the fuel/air mixture, they are now moving quite rapidly. As they are constrained by the connecting rods, they rebound at the top of the compression stroke, before hitting the cylinder head. The wrist pins and rod bearings are made of very hard metal, so the collision is very nearly elastic, and no energy is lost. At each end of the connecting rod are bearings, the spinning of the wrist pin bearing is transferred through the connecting rod and is amplified by the crank bearing. The magnatude of amplification is based on the difference in size between the top end and bottom end bearing, usually about 4:1. The rotational energy is then transferred to the main bearings which are bigger still then the bottom end bearings and they are in pairs. The difference between the initial bearing in the top end and the main bearings is usually about 9:1. This ratio is called the compression ratio because the wrist pin bearing has all of the energy compressed into it and the main bearings are releasing the energy. The spinning of the main bearing is what is transferred through a transmission and finally to the wheels.
In a two stroke engine the power is created twice in each stroke, first in the compression stroke as mentioned above and then in the power stroke. When the pistons rebound, and begin traveling downward with an equal, but opposite velocity. The cylinder volumes thus begin to increase, and the gas pressure drops even lower than it was after implosion. This is called the "power stroke" because the motion of the pistons at this point is more powerful than it is at any other time in the cycle.
This extreme cylinder vacuum causes the intake ports to open, because the intake ports are maintained at atmospheric pressure while the transfer ports have now spent the energy stored which causes a differential. The exhaust ports, however, stay closed because of a vacuum which has developed in the headers. The cause of this vacuum is several fold: First, a rarefaction was caused during the intake stroke when hot exhaust gases were sucked into the cylinders. Second, the heat sinking effect of the long mufflers (whose job it is to cool the exhaust in order to most efficiently extract spent implosion products) has caused the exhaust to cool during the intake/compression cycle. Third, the acoustical resonance of the pipes reinforces the vacuum pulses at certain frequencies. This is why bikes have "powerbands".
When the intake ports open, fresh mixture rushes into the cylinders, immediately neutralizing the vacuum due to implosion. This allows the pistons to move full speed to the bottoms of the cylinders where they again rebound off the connecting rods and begin traveling upwards. The gas is squeezed and pressure rises, creating a superheated condition in the spent gases. The pressure is relieved by the piston rings and vented into the crankcase, where the gases are safely relieved to the exhaust pipe by the crankcase breather and exhaust gas recirculation system. This is called the "exhaust stroke" because this will exhaust all of the stored energy. When the kill switch is pressed on a engine this is where the engine will always stop. To get more power from a 2 stroke engine you need to add on an expansion chamber to the exhaust system. An expansion chamber allows the exhause recirculation system to go through a pressure inversion because the pipe is always bigger then the engine itself. The inversion will make the piston become sucked down faster by the power stroke vacuum which will spin the wrist pin faster and generate more power. As the sides of the expansion chamber expand and contract it sets up a harmonic frequency which further strengthens the acoustical resonance of the intake/compression cycles.