#1 Camshaft timing vs compression ratio
Posted: Tue Mar 28, 2017 7:50 am
Any nerds like me out there might be interested in this clever little thing from a Harley Davidson forum - it's an algorithm for calculating the increase in the actual compression ratio caused by altering the inlet valve timing;
http://www.bigboyzheadporting.com/EVOComp.htm
I actually posted this elsewhere, but it is buried at the end of another thread, and I thought it might be worthy of a posting of its own. The figures for a Harley motor are already entered but are easy to alter. I think you can safely ignore conrod length & depth of top piston land. To save measuring the combustion chamber I use the following formula; the ratio x + y to x equals the stated compression ratio, where x is the volume of the combustion chamber and y is the swept volume per cylinder. So a cylinder of 800cc swept volume and a stated compression ratio of 9:1 will give a combustion chamber volume of 100cc.
http://www.bigboyzheadporting.com/EVOComp.htm
I actually posted this elsewhere, but it is buried at the end of another thread, and I thought it might be worthy of a posting of its own. The figures for a Harley motor are already entered but are easy to alter. I think you can safely ignore conrod length & depth of top piston land. To save measuring the combustion chamber I use the following formula; the ratio x + y to x equals the stated compression ratio, where x is the volume of the combustion chamber and y is the swept volume per cylinder. So a cylinder of 800cc swept volume and a stated compression ratio of 9:1 will give a combustion chamber volume of 100cc.