Recently had a discussion with a friend on the merits of OHV vs sidevalve in a lawnmower application, me taking the “flathead” side.
“Look,” I said, “it costs more, opens up the chance of eating a valve, and lends itself poorly to splash lube. Yeah it breaths better, but…in an engine goverened to under 3000 RPM, you really aren’t utilizing what you’ve paid for.”
“But it uses more fuel!”
“Hey, I get 40 minutes out of a pint. Cutting fuel consumption 20% isn’t going to pay for the price premium this decade.”
“But it produces more power for the same sized engine. A Honda GCV160 and a Briggs Quantum (190cc) have the same rating”
“yeah, but the flathead is smaller above the top of the stroke to make up.”
That had me thinking: outside of racing specs, what difference does “hp per liter” make? I don’t think I’ve ever cared about “how much power per cc” my engine produced. Per $ spent, per lb weight, possibly even per displacement of the entire engine body, yes…but having difficulty imagining caring about hp/cm^3.
So, why such a BFD? Is it indeed relevant to non-racers? What, if anything, would be a better measure?
(As a thought experiment, what engine design would you use if you were told “build me the most powerful engine you can, subject to the criteria that the volume of the engine in total, plus all accessories necessary to allow it to function, must not exceed 10,000cc.”)