repowering my 20v CC have a 150hp 2stroke want to go much smaller

[THEFERMANATOR]

How fast are you trying to go with your 150? I know teh SUZUKI 150 is the biggest 150 there was at 2.7L's, but it was also said to be decent on fuel for it's size. Fuel burn on it should be around 10-12 GPH or so at a 3800-4000 RPM cruise, a 4 stroke will probably get you down to about 6-9 GPH at the same speeds. And like stated above, 90 is the absolute MINUMUM to get a V on plane. And it won't live a happy life doing it. If you don't boat alot, then you will never get your investment back in buying a new engine. Fuel isn't that big of an expense in all reality in owning a boat when you sit down and add up everything you spend money on when boating. Upgrading engine because of fuel costs rarely if ever pays for itself for a recreational boater.