If you are planning on a jet boat, don't think a small block is going to be that much better than a big block on gas. It's the jet that's sucking all your fuel. Small block and I/O = fuel efficient. Small block and a jet= should've just got a big block.
Not totally true.
If you build the small block right and use a spread bore carburetor like a Rochester, keep the rpm around 3800 with a modest AB impeller, with the right (read; light and little) hull. I would expect it would be quite efficient.
Granted, it will be a 45mph boat.
My first jet had a Chevy 327 in it and you could play all day on a 15 gallon bow tank.
This was all in a 17 foot Marlin.
Honestly, that was a seriously fun little boat.
GT
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