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Data entry cells are light blue in color. At A37 is an inch to millimeters converter. All lengths are to be entered in millimeters.  Usage Steps: 1) enter cylinder bore 2) enter piston stroke 3) enter connecting rod length (typical is twice the stroke) 4) enter peak power RPM. 5) enter compression ratio (the cylinder/head volume when the piston edge is even with the top of the exhaust port divided by the cylinder/head volume when the piston is at TDC) if you know it, or use the calculator at the bottom left of the sheet. 6) enter millimeters from top of exhaust port to "deck" (where the top edge of the piston is at TDC) 7) enter the octane of your fuel (MON + RON)/2 or RON x .96 8) exhaust port duration 9) enter the outer squish clearance (piston to head clearance at the far left or far right of piston) 10) enter the inner squish clearance (piston to head clearance at the inner portion of the squish band)  11) enter the inner diameter of the squish area 
12) Compare the recommended Squish Clearance at D1 to what you have entered at D2 and D3. D1 will get your squish volume at E16 nearly equal to what is recommended at A16. The squish violume determines the burn time after peak combustion pressure.  12) Without manipulating the squish ratio at D5 then the perfect squish volume often throws off the squish velocity at D34. It should be the recommended value listed at D37. So usually you have to change the squish clearance for a compromise between the volume and the velocity. Raising the clearance raises the volume and decreases the velocity. But if reducing the squish band size gets you closer to perfection without compromises then just do that. If you need a fatter band then unless you find someone good at adding aluminum to a head then you are stuck with what you've got.  Don't reduce the clearances so much that the hot clearances at F2 and F3 are less than .4mm, otherwise you may encourage detonation.  If the cold or hot velocity is too high then warning messages will display.  If you increase the squish velocity then you have to retard the ignition (make it happen later). otherwise the peak pressure happens too early which can cause detonation. It also causes a power loss due to excess pressure the piston has to push against on its way to TDC.  |