Im having trouble finding info on 390 boat motors. is there anything different in them from a regular truck 390 block? such as heads, higher comp, eta...

I am looking to buy a 390 and my neighbor happens to have a 390 sitting on a stand. he pulled it out of a boat 16 yrs ago and has been sitting there since. he does not know how many hrs are on it or the type of boat it came out of. he told me that since it was a boat motor it has a big cam in it and it also has a dual 4bbl intake with 2 holleys sitting on top. hes asking $1500 for it. i did some research and i can see the intake set up can worth a bit but how much is the rest of the motor worth?

 

Unless it was in a jet type or flat bottom V drive boat, marine engines do not use "big cams" or dual 4 bbl's.

Other that those particular applications mentioned above, marine engines are designed to run at about up to 4500-4800 rpm maximum, give or take a few depending upon the year and the manufacture of the engine.

That means a cam more like a RV, and at best they only need a single 4 bbl to get the proper cfm. Since marine engines do not have "gears" like a truck in different ratios available to shift thru, that means that low end power cannot be sacrificed, so that also rules out a "big cam".

As to other differences, casting / core plugs are brass. Head gaskets are different along with the water pump, carburator and fuel pump. A different front cover (cast iron verses aluminum) is also used if the engine has one. Electrical devices like dist, starter and alternator, as well as the starter solenoids are marine specific.

Basically a marine engine is designed to NOT spill or leak fuel, and also designed to not provide a errant spark that could ignite a fuel leak if one did occur. A marine engine is also designed to run with salt water for cooling, hence no aluminum exposed to the cooling water, UNLESS fresh water cooling is standard.

Not sure at this late date that you could even find marine exhaust manifolds for these beasts.

40+ years in the marine field.... If you have any more questions.

David

 

The seller could have taken it out of a boat, with dual 4s it sounds more like racing use than marine. As David noted marine engines would have different manifolds for non radiator water cooking.

Sorry but a used engine hanging for 16 years wouldn't have a lot of value in my mind. I'd be thinking $300.00 and you guys meet in the middle. Thing is have a fist full of new blues when you meet up again. Cash talks & BS walks.


John

 

I thought I read that the boat FEs had a reverse rotation .

 

There were reverse rotation engines of all makes available, but just being marine does not mean that it is for sure.

Reverse rotations were used in twin inboard installations generally, one standard, one reverse so that the props turned opposite ways to counter the torque thrust as well as making low speed handling equal to both port and starboard.

David

 

x2, and imo, only a high stakes gambler would install an engine that has been idle for 16 years without a teardown. It sounds like a performance build and may be way too high and lumpy in the compression and cam departments for truck use.

 

Thank you for all the replies! definitely more info then what i was finding else where on the web.

 

A boat with twin 390s , I am thinking that would be one fun boat !