If Yamacha doesn't die from the strain on his body then Goku rapes
I read somewhere that...
ssj1 multiplies your base power level by 50
an ascended saiyan (the buff form trunks used) is 4 times stronger than ssj1
ssj2 is 8 times stronger than an ascended saiyan
ssj3 is 4 to 16 times stronger than ssj2 based on how much you've mastered the transformation
Now add that all up and you think that Yamacha with a measly 100 times powerboost is ****ing with Goku?
SSJ3 Goku owns KKx100 Yamcha. Simply because even if Yamcha miraculously survives the pressure, KK is used in bursts. SS is a constant form. Sure, Yamcha may have the upper hand at first but then Goku makes a comeback and owns Yamcha with a Kamehameha.