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Thread: How to improve a 351 Ford Marine???

  1. #1
    Member Roger45's Avatar
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    Apr 2006
    Palmer, AK

    Question How to improve a 351 Ford Marine???

    I have a friend who has a 24 foot ocean boat powered by a 351 Ford marine (apparently one made in Mexico and not Michigan, so is suppose to produce less than 260HP), VolvoPenta outdrive, 4 barrel carburetor, that seems to have a maximum RPM of about 4100 WOT @ 24 knots and burning 20+ GPH. At about 3800 RPM and 21 knots it burns 16-18 GPH but seems to loose performance/handling at this speed. I know this is a common engine/outdrive set up, so I was wondering what sort of suggestions/ideas there are out there to *improve* this set up. Would going EFI be of any benefit? Replacing the cam? Is there anyone/anyplace folks take these to for marine upgrades (for automobiles I would think Coker's in Los Anchorage). We have the winter to mess around with this boat, so any suggestions are appreciated...Thanks in advance for any help!
    "...and then Jack chopped down the beanstock, adding murder and ecological vandalism to the theft, enticement and vandalism charges already mentioned, but he got away with it and lived happily ever after without so much as a guilty twinge about what he had done. Which proves that you can be excused just about anything if you're a hero, because no one asks the inconvenient questions." Terry Pratchett's The Hogfather

  2. #2



    I don't know what 351 is in that boat. I would guess it is a 351 "C". They are good motors and last a long time. It it is a 351 "W" they are good motors too but were not as performance oriented. There is also a 351 "M" which was a good enough motor, but wasn't really a high horsepower engine as its performance was seriously hampered by pollution controls in automotive applications and I have never seen one in a boat. You can build any of these engines to go like hell with 400 plus horsepower. What is it that your friend is looking for? Does he want better fuel economy? More performance? I would say that no matter what he wants that boat really shouldn't be burning that much gas and he probably needs to check the timing, and make sure that the carb isn't running too rich as it really sounds like something is amiss. Timing should be around 8 -10 degrees BTDC and the plugs shouldn't look like they live in gas when you pull them. If the timing is right, a guy may want to swap out that carb or rebuild it if the plugs look like it is running too rich. I had a 350 in a truck that had a Rochestor Carb that got 7-8 mpg and just changing to a brand new Carter Carb it then got 12-14. Just curious, how much does this boat weigh?

  3. #3
    Member broncoformudv's Avatar
    Join Date
    Apr 2006
    Anchorage, Alaska


    That will be a 351W in there and there are tons of things you can do to gain performance and fuel economy on them.

    I would start with a tuneup and doing a compression test or leak down test to see what condition the engine is currently in. If that checks out ok then start looking at the carb because it should be getting better fuel economy than it is now.

    Electronic ignition if its using points now, midrange cam, and head work will all help it out.

  4. #4


    Did it ever wind up any higher? It sounds as if the boat may be over-propped for the load. I don't know about the 351 specifically, but most gas marine engines should turn 4400-4800 rpms at WOT with 4600 being the ideal target. If you can't turn rpms within the proper range, you are lugging the engine resulting in poor performance and poor mileage. If you drop 2 on the pitch it should put you in the right range. The manufacturer should be able to give you the target rpm number. Make sure the engine is tuned, and doesn't have any other issues, and try a different prop.

  5. #5
    Join Date
    Mar 2008

    Default Same engine

    My boat is a 26 ft with a 351W and an older OMCthe book says it's rated at 235 hp. The simple things are the place to start. I don't mean to lecture but heres where I started on mine.
    1. timing 8-10 BTDC
    2. ignition. I replaced my older ignition with a new mallory complete unit wire, plugs everything. WOW is all I can say.
    3. Carburetor. Hate em/ love em. They cause me more heartburn than anything else. Get a good Holley 4150 vacum secondary 600cfm carb. Simple as dirt and easy to tune, jet, etc they are a fairly indestructable carb and parts for them are everywhere (a big plus)
    4. Just for grins and giggles check compression on all 8 cylinders if a couple are down then.....
    5. I think they had it right on the prop too. See what prop you have and check out the cost of a new one the next size lower. (If you have a 21 pitch try a 19) besides the original prop is a good spare to keep on board. The weight of the boat and hull type as well as how much stuff your hauling really play into the prop selection.
    6. Trimming out the boat. Bow down/up? Have you found the sweet spot on that hull/engine combo where RPM's free up and the boat sets best. Simple but my buddy ran his a whole year with the bow down all the way. Howled like a scalded cat about fuel, power etc. oops.

    The Mallory system and Holley carb made a world of difference on my 351 and I burn 9gph at 3900 rpm at about 27 mph on my gps. I rarely if ever run up past 3/4 throttle. I just don't have the need and that is moving along in that big old tub. Just some idea's

  6. #6
    Moderator bkmail's Avatar
    Join Date
    Apr 2006
    Palmer, AK.

    Default similiar issue...

    A friend of mine had this motor in his 22' jetboat. He was burning lots of gas and having trouble getting performance out of it. A shop in town turned us on to the fact that his secondary butterfly's in the carb were not opening. They were gummed up from old fuel and wouldn't open properly. A good dose of carb cleaner and some manual working of the butterfly's and she was like new again. Very simple fix and she ran well after that, both performance and fuel economy improved. Just a thought for ya!

  7. #7
    Member greythorn3's Avatar
    Join Date
    Sep 2006
    Chasin the ladys! away!


    take it out and put a 460 in its place!
    Semper Fi!

  8. #8


    take it out and hang a 350 yamaha off the back

  9. #9


    351C was made in Cleveland
    351W was made in Windsor
    400 is based on the 351C

    Totally different motors, including the block. The 351C is a killer motor, the W is a dog.


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