Port scavenged engines can be just as efficient as four strokes, provided no fuel goes out the exh like old outboards. Gassers like optimax, hpdi, etec solved the fuel-out-the-exh issue by going with direct injection after the exh port closes. Good efficiency for gassers, in some cases better than four strokes. Diesels in the same category, capable of good thermal efficiency.
One bug is that port scavenged engines will throw some lube mist out the exhaust, even if direct injected. Any of these engines therefore have little hope of meeting strict emission regs. That's what killed the Detroit two-stroke. These are in the same category.
The 67% thermal efficiency claim is pure BS, and once seeing that, the project lost all credibility in my mind.
Machining a precise curved bore is doable, but tricky. Same with pistons. Doable. Just takes clever jigging on a boring/turning setup. A standard mill or lathe won't get it.
These things pop up all the time. I think many are motivated by trying to soak unsophisticated investors out of R and D money.
If someone truly has a better engine architecture, you better believe they will keep it quiet until they do enough development to secure patents. And that level of development would include a running prototype capable of dyno testing.
No running prototype? Not viable.
Building a prototype is not that difficult. The Wright Bros. built their own engine without being engineers or trained machinists. That 110yrs ago. CNC and CAD and CAM makes even whacky shapes easy now.
If I get supremely bored, I look on utube for whacky engines. Amazing how many hundreds are out there. And none but the Wankel have really ever challenged the recip piston engine. And the Wankel was from way-back, too.
Some have mindblowing levels of compexity, that can be impressive.
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