So long as you're comparing apples to apples, the HP numbers of the 2 valve 169cc engine aren't low...
...You may have noticed the SYM HD 200 (171cc) has 15.2 HP, but it has a 4 valve cylinder head
https://m.youtube.com/watch?v=PXD_AvKbCMgHonda makes a motorcycle called the VFR800 and it uses a 'stone age' version of 'VTEC' (Honda's name for variable valve timing) where at lower RPM, 2 of the 4 valves for each cylinder remain closed (effectively making the engine a 2 valves per cylinder design)... Enjoy your 2 valve cylinder head advantage, for its rocket off the line, starts...😜
...Okay, so we know a small displacement engine with a CVT, spends its life screaming at high RPM...
Upon further examination of the video title 'DOHC vs OHV' (as if DOHC automatically means 4 valve heads...🙃) the Engineering Explained guy posted, I have to add this
http://www.chinonthetank.com/2012/12/how-cb450-torsion-bars-work/ DOHC with 2 valve heads...😉 But what really made this engine unique is the way the valves get closed.. 🙄 Take that, Ducati!
https://m.youtube.com/watch?v=ocfIYUc5bpUTaking engines to thermonuclear proportions, this was Honda's attempt to compete against 2 stroke racing engines, after they were denied a bend in the rules to make a 4 stroke 500cc V8...
http://justacarguy.blogspot.com/2018/01/the-only-oval-piston-dual-con-rod.html