repower

[dohccobra]

Hello all. I just purchased my first boat, a 1985 21' Celebrity Runabout Bowrider. It currently has a Mercruiser 260hp inboard outboard setup in it. I am mostly a car guy but i want to try boats. I have figured out that the engine in there is a 350 small block chevy. The motor is no good in the boat. What are the differences between a car and marine engine. can i just use another small block in this boat? will the outdrive ( i think thats what it is called) handle extra power? the other power option i have that i think would be cool is a 7.3L powerstroke. Any way you can help is greatly appreciated.

[AroMarine]

I am not a mechanic and dont play one on TV but I have been through a fair number of repowers mostly diesel but some gas. So here is my two cents. Marine gas engine short blocks should be built as a commercial/truck engine ie heavier rods and pistons. A boat is continually pushing uphill. Also for a newbie take some time to learn about your cooling system heat exchanger or raw water, and most importantly your alternator and starter must be spark proof. As you did not mention make and model of outdrive I am going to guess Mercruiser and for that hp I dont think it would take the torque of a 7.3 and in a 21 the extra weight and lower rpm would probably be a poor choice for a repower.

[rasorinc]

If the block is not damaged why not re-build it? Be cheaper then buying a MARINE ENGINE. And in the re-build you can add HP to what you want easily up to 300hp or so.

[dohccobra]

Originally Posted by AroMarine

I am not a mechanic and dont play one on TV but I have been through a fair number of repowers mostly diesel but some gas. So here is my two cents. Marine gas engine short blocks should be built as a commercial/truck engine ie heavier rods and pistons. A boat is continually pushing uphill. Also for a newbie take some time to learn about your cooling system heat exchanger or raw water, and most importantly your alternator and starter must be spark proof. As you did not mention make and model of outdrive I am going to guess Mercruiser and for that hp I dont think it would take the torque of a 7.3 and in a 21 the extra weight and lower rpm would probably be a poor choice for a repower.

ok, i will do some research on the cooling aspect of the engine. i am not sure of the outdrive but yes the motor is mercruiser. and as for the 7.3 thanks for the input.

[dohccobra]

Originally Posted by rasorinc

If the block is not damaged why not re-build it? Be cheaper then buying a MARINE ENGINE. And in the re-build you can add HP to what you want easily up to 300hp or so.

i think i am going to rebuild it. i might be damaged but block can be found for cheap. i am taking it to a machine shop this week to have it magnafluxed and pressure checked. i think i will add to the hp when doing rebuild. what do you think max hp should be 300-350 maybe?? do you think this boat will be pretty quick. i read the weight of boat minus ppl and fuel to be about 3200?? thank you for the help

[rasorinc]

Here are the specs for the current GM 5.7L rated at 292hp also specs for the 5.0L
http://www.gm.com/experience/technol...700_Marine.pdf
http://www.gm.com/experience/technol...000_Marine.pdf