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CG and CB motors will never make that kind of power. 2-valve pushrod motor is a completely different class. Even the Virago V-twin motor only pushes out 19hp out of a 250cc twin. It's a 2-valve-per-cylinder single overhead cam aircooled motor.
Going 4-valve heads is a way to get more power.
Tighter tolerances and higher compression is a way to get more power. But this generally requires water cooling. Spinning the motor faster is a way to get more power. But pushrods can't go that fast, so overhead cams are required. Timing the exhaust and intake valves more precisely is a way to get more power. And that means independent intake and exhaust cams.
All of this adds up to make a far more complex motor than the CG mill. But also a far more powerful motor. And modern machining and metallurgy allows it to still be completely reliable.
Charles.
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