Just came across another boat with a 409 in it about 2 weeks ago. Big boat and way to much money for even a running 409.
It depends on the 2 engines your trying to compare if looking to replace a high horse solid lifter high compression 348 with a low compression 409 with a hydraulic cam there probably won't be much gain maybe even a step back,but if your comparing it to a low compression hydro cam 348 then there should be noticeable gains.If your going to have to rebuild the engine before use by all means use some of the available higher compression forged lightweight pistons to get more gain and to build a solid foundation for possible future power upgrades.BTW, what kind of horsepower do the later marine engines have? ( I'm told that the one I am interested in is a '64. It has an X on it.)
I'd like to get a power increase over the 348. Any guesses about what kinds of increases the easier upgrades like dual carbs and/or a mild cam will give?
I suspect that 270-280 hp rating was at around 4000 rpm though,theres no way an engine that big would be that mild with a solid lifter cam unless they used the super low compression truck pistons in them.I know the ford marine engines were around 9.5 compression or better the big truck and industrial engines were really low compression but they were specced to survive even in hot dusty environments,the marine engines had plenty of cooling capacity available to support a higher state of tune.If chevrolet was similar to ford in how they built their marine engines it wouldn't surprise me if their lower horse big boat motors were very similar to the 340 409 shortblock with maybe 333 heads and a marine specific cam.If this is the case I would expect an engine like that to make closer to 325-350 horsepower if spun up to higher rpms.If someone has had a marine 409 apart did they see if it had truck pistons or something more like 340 horse pistons in it?Also was the intake more like a 340 horse or a truck intake?Most of the Marine 409 engines were in the 270-280 HP range with solid lifter cams
These engines came with aluminum intake and dual point distWhile I can't speak for all 409 marine engines,over the years I've seen pictures of several.All of those used the truck/industrial pistons and the 333 head.Another reason for the lower hp ratings likely comes from the "suck egg' exhaust manifolds that they used.
Pat only has 1???????