Thanks Pete, Interesting!
But I suggest that when comparing engines, you need to minimise variables. e.g. the difference between the VW and Subaru is a lot of other factors I think (Not knowing those specific details): Possible Cam/valve-timing, Fuelling system (manifolds and carb sizes), compression ratio, Displacement, and Valve sizes, as well as the 2-valve : 4-valve difference. I did some "Home experimenting" with Motor-cycle engines, as I had 500cc Triumph engines, carbs, cams, and exhausts to "ring the changes". e.g. When commuting I wanted the "trials engine" cam and timing and a single carb was OK for this. Just easy to ride with "apparently" good low-down torque for ease of moving away from the following traffic at Traffic Lights. And that was true with low and high compression pistons, with appropriate ignition timing and carburation. But the top-end performance was really lacking.... Which was improved by the "standard" cam (valve timing with increased overlap). But of course, for "thrashing around the roads", the best was a different cylinder head with bigger ports, sporty cams, higher compression of the limited edition "500C" top-end. (This was sold as a racing kit in the mid-1950s, and when I used it on a "standard" crankcase it ripped the crank-case apart! - It needed the later crankcase which had thicker walls and bosses all over). But I did learn "hands-on" that without variable cam timing, the factory produce a very good compromise of cam timing for commuting and highway use. My point for a book of "small" engines for models was that if you need the engine to replicate a decent performance for powering an aircraft, boat, car, etc. then you should consider a different cam and timing to an "idling" engine.
When I worked for a car manufacturer, the engine test for valve test was a long period of idling. Actually, although most testing was planned for the Engine Dynos, it was the one test that could be done on a simple test rig - just like a rig for demonstrating an engine at Model shows. I.E. a sturdy frame, fuel tank, ignition and local cooling system. The only loads on the engine were the Alternator for Ignition, battery charging and electric fan for the radiator. The reason for Idle testing for cam and valve gear wear, is that at high speeds, the dynamic tuning of the valve system causes cam followers to slide-up then "leap over" the crests of cams reducing contact pressure considerably on the lowering side, before catching the full pressure when the cam is nearing the bottom displacement region. So at speed, the high points for wear are when the valve springs are at their lowest pressure for cam to operate, whereas at idle, the cams wear on the crests, due to the higher spring pressure on the oil-film and cam face.
Complex stuff this "Engineering", I reckon!
Have you read "Tuning for Speed" by Phil Irving, or any other books of engine tuning? - there must be thousands out there. The same fundamental rules apply to small engines, and "idling" engines, so there is no need to re-invent the wheel, just maybe explain different applications and designs?
Enjoy,
K
