Higher compression is gained by many different ways but lets talk about pistons. In a 4 stroke a taller piston,measured from the wrist pin hole to the top of the piston creates higher compression because the extra height of the piston will compress the air/fuel mixture tighter,just as it would in a 2 stroke. BUT in a 4 stroke the intake valve and exhaust valve control the flow. At some point if you keep adding height to a piston it would eventually come in contact with an opening valve. In a 2 stroke there are no valves to control intake and exhaust but there are intake and exhaust ports as well as transfer ports. In that situation a taller piston will,depending on intake or exhaust port not fully open them due to the cylinders design. So the easy way to up the compression is to mill (shave) the head that bolts to the top of the cylinder. When you remove metal from the head you are making the head closer to the piston which actually creates less cylinder area. And when you put the same amount of fuel and air in a cylinder with less space then when the piston comes up to Top Dead Center that mixture will be compressed tighter. You are limited as to how high of a compression you can go to by fuel. You can only go to about 13.5:1 and still run automotive fuel. After about 15:1 you have to run Methanol. At about 17:1 you get into Nitromethane fuel.
I would rather have a sister in a whorehouse,than a brother with a quad!!!!!!!!!!!!!!!!!!!!!! Still walking the "Tightrope"
Just Too Addicted
Arm chair racerJust too addicted
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