The Combustion Chamber. ( Not Your Average Chamber Of Horrors)
In order for an engine to make HP and Torque, filling an engine's cylinder with plenty of cool air and evacuating the exhaust efficiently at Hi -RPM is an essential factor. If the combustion chamber dynamics are marginal, then the capability to maximize a engine's cylinder's power output will not occur.
During low RPM an engine’s output is about efficient combustion, not about the airflow capabilities of the cylinder head. This is due to the fact that at low engine RPM’s there is ample of enough time for the air / fuel mixture to fill the cylinder.
Increasing the cylinder head’s airflow 75cfm (cubic feet per minute) does nothing at 2,000 RPM based on the reality that there is no shortage of the air / fuel mixture at that RPM. At the other end of the RPM spectrum though, 75 additional cfm at 6,500 rpm, will result in a HP and Torque gain because there is about 18 milliseconds to fill the engine’s cylinder. Low engine RPM output is controlled much more by the air / fuel mixture’s quality, the cylinder head’s port velocity and motion, and the compactness of the combustion chamber.
If the air / fuel mixture quality and the atomization is adequate while traveling thru the carburetor, then after this point changes will occur. When the air / fuel mixture moves down the intake port the fuel will fall out of suspension. The slower that the intake port moves the air / fuel mixture the air / fuel suspension problem becomes larger. That is the reason why cylinder head intake port volumes need to be only large enough to accomplish the job and not larger than necessary. The correct cylinder head intake port velocity helps generate swirl, as long as the intake port is targeted in the right direction.
Carbureted SUZUKI engines, have a strong swirl generation in the mid to high lift intake valve area, this swirl characteristic will distribute the air / fuel mixture throughout the cylinder without centrifuging much of the air / fuel mixture out onto the cylinder wall. If the swirl generation is high enough to cause the air / fuel mixture to centrifuge out, then this is an indication that the fuel is not sufficiently atomized when entering the cylinder head’s intake port.
The piston’s crown is a major portion of the combustion chamber, in fact it should be consider the floor of the combustion chamber. In order to reach the objective of effective combustion, the faster the air /fuel mixture burns, the higher the compression ratio the cylinder will tolorate. The combustion chamber cavities that are between the piston and the cylinder head that have ranges from 60 to 120 thousandths appear to initiate detonation.
Speeding up the combustion process can reduce detonation. This is able to be accomplished due to the reduced time that the unburned air / fuel mixture is exposed to the radiated heat of the advancing flame front, which will allow the unburned air / fuel mixture to be cooler, in addition a faster combustion rate requires less ignition timing advance, resulting in a smaller rise in the cylinder pressure on the upward piston stroke after the spark plug has fired. A reduction in the peak cylinder pressure and temperature is created because the combustion process is faster and the pressure rise on the piston’s downward stroke will be higher which will create a greater output (more HP) of the cylinder.
In order to reach the objective of creating more HP and Torque it is mandatory that air / fuel charge agitation and combustion mixture motion is speeded up. Intensifying the air / fuel random mixture motion within the combustion chamber swirl pattern just before ignition to the air / fuel mixture takes place can be done by maximizing the quench area action. Reducing the quench area clearance, the cylinder’s burn rate and combustion effectiveness are improved to the point where, even though the the engine has a higher compression ratio, it is less likely to detonate.