I have a radical 406 small block pushin 600 hp .I would like to bolt it down to a sheet of 4 x 8 marine grade plywood.connecting the back of the crankshaft to a 1 1/4 stainless shaft with a nybrill 4 blade prop.i am planning to connect the throttle return spring to the opposite side of the intake so when i start the motor its wide open throttle ( wot ).does anyone think that this would be to much power to weight ratio??

No not at all.. What makes you think that. I have got an even better idea. Put on a set of water skiis, strap the motor to your back, and have at it.

Maybe the Jet Boat guys could wedge a big Berkley up the arse..

Oh wait, never post when drinking!

Glad you said marine plywood. Hate to see you go thru ALL the rigging and use OSB board. That stuff will absorb water like Bounty paper towel and slow you way down. Can't have that now can we!

I'm thinking that if you take a 4" hole saw and cut a series of holes around the engine mount area and maybe in the block itself you may get the weight down to an acceptable level and really achieve the desired speed and efficiency inherent in this type of craft.

I would also recommend a very heavy spring-possibly a garage door spring-for the throttle. There may be a desire to pull back on the throttle after planing off and a good heavy spring will preclude this action.

Another thought-have you considered turbine power??? One of those and a prop from an electric trolling motor directly coupled and you should see triple digit speeds.

if you cut the 4 x 8 into 2 4 x 4 sheets then screw them back together with about 6" of over lap you will have a step hull good for an extra 10 mph but it may spin out in the turns

Why the plywood?
Just hammer a nice flat spot on the oil pan. Won't need any more surface area that that anyhow.

I am, however, concerned about the prop torque. A Duo Prop setup would track much better instead of spinning in circles like Curly (woop woop woop).

Maybe you should just put a paddlewheel on each end of the crank and ride it sideways??