differences in Vanguards

[fmints]

Hello everyone! I'm interested in finding the difference between the 14, 16, 18, 20, 21, and 23 hp briggs and stratton Vanguard engines. I have a 16 hp vanny and was told that the only difference between the 16 and 18 is the intake manifold and the carburetor. I was also told you could ge a rev kit for these engines but i dont know where to get them. also,,, can you jet the carburetors like on a motorcycle to get more hp out of them. Thank you for all of your help in advance.