A mistake on the previous post, last sentence. I like more lobe separation, not less, for this application. Now I need to make another choice. The 865 cc pistons increase the displacement 9.5 percent and the 988 pistons increase displacement 25 percent. The 790 cc cam had adequate breathing at the 7,500 rpm target engine speed I used. These questions I need to answer. Will the new cam give me adequate breathing at a 7,500 rpm target speed with 865 or 988 cc displacement increases using the valves I have, or do I need a bigger valves? Cams are a complex subject and I need to make things simple so I can arrive at an answer. I need to work quickly using the tools that I have, the kitchen table, a pencil, graph paper, a calculator, three bottles of beer, and a pot of coffee. It will take two posts to show what I do.

First, I plot degrees duration on the x axis and inches lift on the y axis on some graph paper. Next, I plot the cam opening, maximum lift, and cam closing points on the graphs. These lifts and durations are from the cam data and the worksheets. Now I plot the valve lift curves on the graphs. These curves can be based on real data obtained by using a dial indicator to measure valve movement and a degree wheel to measure rotation. My engine is apart so I cannot do this. I draw the lines on the paper using a french curve and an approximation of a sine wave pattern. An educated guess and it is good enough for now.

The flow through the valve opening is assumed to occur at 0.050 inch lift or more. Lines are drawn across the curves at this lift. I measure the areas under the curves and above the lines in square inches then I convert these measured areas to inches lift x degrees duration.

Now, I figure out the valve perimeters and multiply them by the lift x duration values. This is on the worksheet. This tells me, in a rough, approximate, and abstract way, the opening areas between the valves and the seats.