I was thinking about both of you on Friday. That tracer idea reminds me of something I did back in hi-school metal shop to make a complex shape.

There is a formula in Harold Bette's book "Engine Airflow." It empirically equates intake flow to horsepower. Intake flow tops out at 230 cfm at 28 inches water for the complete system using valves, port, manifold, carb, and air filter. There are two cylinders. The "Coefficient for Estimating Horsepower" is 0.257 (See Page 82). 2 x 0.257 x 230 = 118 HP at the flywheel at 60 degrees F, 29.92 inches pressure, and 0 percent humidity. This corrects out to 117 flywheel HP in the Dynojet Standard atmosphere of 68 degrees F, 29.92 inches pressure, and 0 percent humidity. A traditional wild guess at drivetrain loss is 10 percent. 117 x 0.9 + 105 HP This is almost exactly what the dyno read during the tests last summer.

Peak power RPM is also calculated empirically based on a formula in Bette's book. "Coefficient for RPM" 1196 (See Page 83). Displacement is 30.35 cubic inches per cylinder. Air flow is 230 CFM, as in the previous equation. Peak power RPM is (1196 / 30.35) x 230 = 9,063 RPM. This is almost exactly what the dyno says.

The preceding formulae predict performance from a fully developed engine. This is an air cooled twin with side draft ports. There likely is not a lot more performance to be had - unless intake air flow is boosted. A successful tuner of these things told me ten years ago I would need to go to a bell mouths on the carbs like I am designing now. It was something I never had time to do, until now. He also said the motors needed to be spun up to ten grand. This was something I could not do until now. My motor building skills needed to be developed.

It is a long road from dreaming about going fast to actually doing it.