357 cc is how many hp?

Divide x 30cc .....(= 1 Horse Power)

^this is not correct. I am not talking about the 12 hp, for all i know it's correct. I am talking about the way it was calculated. Engine displacement has absolutely nothing to do with power. I don't know where or who you got this formula from, but it is incorrect for many reasons.

(1) as stated before, horsepower is not a function of displacement

1hp = 550 foot-pounds per second

(2) you are saying that all engines...regardless of thousands of variables have the same efficiency.

Neither answer has any completeness. HP is not a function of displacement alone. By way of example, Kawasaki makes an FB460V that is 12.5 HP and an FC420V that is 14 HP. Now that 460 is the cc's of the engine just as the 420 is also cc's. The smaller engine has more horsepower because it is OHV which is more efficient.