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Thread: Increasing the performance of a 351 H/M

  1. #16
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    The general rule is 15-17 hp equals 1mph increase. Dragging a Volvo od that equation may be out the window.

  2. #17
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    on a 7k budget you will get more bang for the buck in the chevy world than you will in the ford world and the chevy will bolt up to the 270

    the chevy and volvo combo is pretty tough too
    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
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    When I'm home again,
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  3. #18
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    Brand new 325HP/350 = about 5K

    Quote Originally Posted by mattyboy View Post
    on a 7k budget you will get more bang for the buck in the chevy world than you will in the ford world and the chevy will bolt up to the 270

    the chevy and volvo combo is pretty tough too
    Matt has a good point. Lots of options for SBC and marine accessories are much more accessible.

    You could pull your original 351 H/M and accessories and store for if you or someone else ever wanted to return the boat to it's original configuration.

    I sold my 1975 18C in favor of a 1987 20 Minx because of the Merc drive had trim and was much more available. I do like the 18 Classic boat better and plan to go back to one at some point down the line.
    Thank you, Patrick
    1994 18' Classic 350Mag Alpha

    Previously owned Donzis -
    1996 22' Classic, 502Mag Bravo
    1987 20' Minx, 350Mag Alpha
    1975 18' Classic, 350Chevy Volvo 280

  4. #19
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    Quote Originally Posted by mattyboy View Post
    The rule of thumb is for every mph you want to go faster budget 1 K so I would get a figure for your hull work and see what you have left for powertrain
    Sounds reasonable...Is there specific hull work that's recommended? I'll have the deck off next week. I could do a two-stage project - first part as you recommend and the second part the powertrain.

    Do you think I can get parts to rebuild my 270 Volvo?

  5. #20
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    gas tank, transom, and stringers

    Quote Originally Posted by sandslot View Post
    Sounds reasonable...Is there specific hull work that's recommended? I'll have the deck off next week. I could do a two-stage project - first part as you recommend and the second part the powertrain.

    Do you think I can get parts to rebuild my 270 Volvo?
    I'd plan to replace the fuel tank if you are pulling the deck.
    Check the stringers and transom for cracks and or rot. Unfortunately a 45+ year old boat is bound to need some work...
    Thank you, Patrick
    1994 18' Classic 350Mag Alpha

    Previously owned Donzis -
    1996 22' Classic, 502Mag Bravo
    1987 20' Minx, 350Mag Alpha
    1975 18' Classic, 350Chevy Volvo 280

  6. #21
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    Bigest hold back on a 351 ford are the cylinder heads they were designed for a 289 even though the older 351s had slightly larger valves and ports. Best to go with aftermarket heads as a start. First thought is do you want cast iron or aluminum? Fresh water or inclosed cooling system aluminum ok for fresh water. Cast iron for salt or aluminum with a coating thats about a 1000.00 option or inclosed cooling. Heads are about all there is holding back a ford compaired to a SBC.
    Scars are tatoo's of the fearless

  7. #22
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    A mechanical resto would be all fuel lines and tank as well as new wiring then powertrain
    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
    well raise a glass and think of me...
    When I'm home again,
    boys, I'll be buying!

    My Ride

    Come Join Us on The Queen Of American Lakes



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    www.lgdonziclassic.com

  8. #23
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    Take a look at this thread about some restoration work I did on an old 18 Barrel Back;

    http://www.donzi.net/forums/showthre...Barrel-Back-18

    If you have any questions, don't hesitate to ask.
    George Carter
    Central Florida
    gcarter763@aol.com
    http://kineticocentralfl.com/


    “If you have to argue your science by using fraud, your science is not valid"
    Professor Ian Plimer, Adilaide and Melbourne Universities

  9. #24
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    Im in the completion phase of two 418cid 351w. Ill keep you posted. Forged pistons, cast Scat crank, H beam rods forged. Roughly $1500 balanced with Harmonic Balancer...each plus machine work.

    427 Windsors were much more (2k+) due to only being available with forged crank. This was little different in price from rebuilding my reciprocating stuff with new pistons.

    I think we're at 10 to 1 compression. Ported and big valve 1969 4bbl heads. Offenhauser 360s, Holley 750s. Comp Cams.
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    24' Nova Sprint 1971
    You are what you drive!

  10. #25
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    Fwiw...just noticed your budget. Mine is 10k for the two engines. Long blocks built by machine shop. New cam and kits (one custom ccw). 700 worth of Mallorys. A new 750 Holley. 3 blocks pyrchased in addition to 2 i had. The plight of dealing with a bunch of non running parts and no backstory.

    Machining and modify standard 69/70 4bbl head to match other big Chebby valves and matched porting of other 3 heads (as i had 1 cracked head). Same with 1 Offenhouser 360 intake.

    I was told NOT to buy the $700 per set aluminum 351w Chinese complete heads off ebay. They would have saved a ton, but the machine shop has seen seats fail in 50 miles.
    24' Nova Sprint 1971
    You are what you drive!

  11. #26
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    If you want more speed, raise the drive up 2".

    Jeff
    " Just piercing the surface"

  12. #27
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    Quote Originally Posted by Craig S View Post
    Im in the completion phase of two 418cid 351w. Ill keep you posted. Forged pistons, cast Scat crank, H beam rods forged. Roughly $1500 balanced with Harmonic Balancer...each plus machine work.

    427 Windsors were much more (2k+) due to only being available with forged crank. This was little different in price from rebuilding my reciprocating stuff with new pistons.

    I think we're at 10 to 1 compression. Ported and big valve 1969 4bbl heads. Offenhauser 360s, Holley 750s. Comp Cams.
    Dont know your heads air flow but well done there small for that many cubes. Also you will have a realy ruff time finding spark plugs in the proper heat range as most popular plug for a sbf with 18mm plugs have been discontinued. Either too hot or too cold is all thats left. Have been dealing with this for years on my 460 and 302.
    Scars are tatoo's of the fearless

  13. #28
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    Structural improvements for 60+

    Quote Originally Posted by mattyboy View Post
    honestly at this point the boat is a candidate for at least a full mechanical resto with some glass work for the stringers to beef them up for the increased speed. Not to mention the fuel system parts for the Volvo can be found but some parts are not around anymore same for the HM stuff so that needs to be taken into account
    What's your budget?
    We discussed powertrain improvements needed to go 60+....what about structural? I'm thinking I'll add a few stringer braces throughout the entire hull. Seems to be a few short. I already have a large gray-colored "triangular" one in the bow (about 2' from tip - can be seen below)), but seems more are needed. It also seems to me more structure is needed to strengthen the cockpit-hull interface too. Suggestions/thoughts?
    deck of hull donzi.JPG

  14. #29
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    usually once the main stringers are confirmed as solid and dry or replaced beefing it up is done with gussets that run port to starboard and some also use coring to make the hull solid higher speeds mean more torque and pounding stresses on the structure make sure you have weep holes and seal everything
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    When the sky is grey,look out to sea.
    When the waves are high and the light is dying,
    well raise a glass and think of me...
    When I'm home again,
    boys, I'll be buying!

    My Ride

    Come Join Us on The Queen Of American Lakes



    Contact Us

    www.lgdonziclassic.com

  15. #30
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    IMHO, tying the gussets into the hull sides will generally result in the bond in the hull sides will eventually break loose,
    because the bottom and the sides move differently.
    If you want stronger/stiffer hull sides, add another course of stitchmat to them.
    If you want a 450 HP engine in an already stiff 18' boat, maybe add a couple of gussets that end a few inches from the hull sides.
    If we were talking about 1000 HP, we'd be having a different discussion.
    George Carter
    Central Florida
    gcarter763@aol.com
    http://kineticocentralfl.com/


    “If you have to argue your science by using fraud, your science is not valid"
    Professor Ian Plimer, Adilaide and Melbourne Universities

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