Just to clear some confusion:

-"compression ratio" is the ratio at which the piston "theoretically" displaces air volume in the cylinder. 10:1 means the cylinder volume with the piston at bdc is 10 times greater than with the piston at tdc.

-"corrected compression ratio" is the ratio between the cylinder volume measured when the exhaust port closes and the cylinder volume at tdc.

-"compression" is just a reading that MANY factors will effect, including corrected compression ratio, static compression ratio, ring wear, etc.

-"volumetric effeciency" is the term I believe most of you are searching for. Pipes, turbos, cams, intake design, and primary compression ratio(2-stroke) are some of the things that effect this. Especially turbos and superchargers. What this term means is a ratio between swept cylinder volume and actual air volume that enters the engine while it is running. Most NA 4-strokes run about 90% VE. In other words, an XR100 will intake approximately 90cc of air at torque peak for every combustion cycle. A good 2-stroke design will run WAY over that due to the tuned pipe ramming air back in the cylinder and the pressurized/forced induction created when the piston pressurizes the crankcases.

The design of the front NSR cylinder allows for a better pressure wave from the intake/crank into the cylinder, or what you can now term "better volumetric effeciency". The HRC 0.6mm base gasket helps this by reducing both the compression ratio and corrected compression ratio by just a tad to help put it more in tune with the other cylinder. It is not the best way to fix this, but it is the easiest and, in some race classes, the only legal route.
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS


Last edited by Wrench. on Fri May 06, 2005 2:56 am; edited 1 time in total