Yes Mark I have that Dirt Bike article too. The poms were experimenting w this before CCM. Somebody was doing it on an old 500 Ariel before that.
Seems to me you could potentially get some supercharging effect cos you get 2 bites of the cherry - 2 pumps of the crankcase to one inlet stroke in the top-end. In theory at least.
But the friction/throttling losses thro'out the system would kill it at any reasonable rpm on a single cylinder design I would think. In a spark ign engine, throttling losses are one of the major causes of inefficiency (compared to compression ign engines), & in this engine, you not only have a long inlet tract (on an OHV/OHC engine), but the inlet charge has to pass thro 2 reed valves, a crancase & a poppet valve.
Volumetric efficiency wouldn't be that great in the end I wouldn't think. My guess is that whatever supercharging effect you achieved would be negated in losses thro the inlet system at higher rpm. There maybe some gains at low rpm. (Perhaps it might suit a trials bike application) I'd think there'd be noticeable lag on throttle response w that loong inlet too.
But the engine on the hhed website (mentioned above) is quite ingenious. Running as an opposed twin w 180deg crank overcomes some of the probs (eg less reedvalves needed) & the side-valve configuration makes a much more compact design w shorter inlet tract. But sidevalve combustion chambers are inherently thermodynamically & volumetrically inefficient (compared to OHV/OVC ones) & I'm more than a little skeptical of their claim to 37% thermal efficiency. (There is an asterisk beside that claim but I don't see any footnote explaining the asterisk). Not sure the supercharging effect would be that great either in that design but there should be some. No question over the quality of engineers behind the project tho.
The Norton Wasp engine mentioned above was different altogether. It was a stepped piston 2 stroke design which doesn't use the crancase, & you can get almost as much supercharging as you want w that design. The poms were quite hopeful of that design & as I recall it was Bernard Hooper developing it - an engineer w lots of runs on the board in Brit m'cycle design/industry. However it seems to me the pumping losses in that design (esp in single cyl variants) would almost kill it's potential benefits too, tho someone may yet prove me wrong on that.
I remember an article in one of the engineering journals back in the 70s about a radial 4cyl stepped piston engine of about 1600cc being developed in Melbourne for use in cars. Never heard anything more about it since. Obviously it died too.
