I just had a catastrophic failure with my 350 rocket in my jet boat, early cold weather froze the water in the block out hunting , cracked the engine block..

Having a hard time to find a small block around here but found a few big blocks..

Are the engine mounts in the same place as a small block , the bell housing mounts should be the same but will my exhaust logs off of the small block fit on a big block ?

 

All should fit. The BB's a couple of inches wider, but the exhaust ports are otherwise in the same place, so if your pipes have a bit of flex, they should fit fine.

BB and SB automotive exhaust manifolds are different sizes in terms of port size and overall volume (though they will bolt up to one another), but I don't know about marine parts.

- Eric

 

If you upgrade your jet boat to a big block I think you'll enjoy the increased power you get.

 

The SBO can make some serious power for your boat with the correct components, BBO makes good Tq too, But heavy!

400-500hp sbo is easy, even with iron heads. .02

 

I have to ask ... have you looked into having your block welded? With the improvements in TIG technology, a cracked block doesn't have to be a death sentence anymore (although it doesn't come cheap). I know enough about boats that personally wouldn't try changing to the BBO without consulting a boat mechanic. They both take the same marine manifold (I presume you've checked them for freeze damage?) Your jet impeller is horsepower matched to the engine ... slap another 100hp in there and you may well find yourself stranded with a snapped shear pin. The additional mass sits higher and may well mess with your trim .. and clearances may be an issue.

For those not versed in boats .. inboard engines don't generally use closed loop systems with a radiator. They draw cooling water from the water they're sitting in, run it through the block and through the exhaust manifold and then dump the heated water back out.

Gotta ask ... what was your fuel consumption like? Last boat I was looking at (cruiser, naturally) I was staring $400/day in the face. Poor guy couldn't give the damn thing away.