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  1. #11
    Registered bouyhunter's Avatar
    My Boats:
    24' Pantera
    Join Date
    Aug 2002
    Apache Jct. AZ
    Quote Originally Posted by f311fr1 View Post
    The blocks should be four bolt mains. The cranks are cast, the rods are the small bolts, the pistons are cast. The heads, cams, intakes, carbs, and exhaust can all be upgraded. You should be able to get 400 to 450 HP with reliabilty. If you don't do your own work pick a reputable engine builder. There are several on here.
    That list is everything that has been done to my motor short of the heads, and Carb should be here tomorrow. Going to Dyno in a few weeks, motors ready, but I want to wait until I get back from Miami. My builder is guessing in the 375-400 hp range. That's enough for this boat, and I wasn't planning on building a rocket ship.
    I've got about $1500-1800 in parts, not including builders labor. Exhaust was done by previous owner 6-9 Months before I bought the boat, so I didn't have to take that hit.
    Joe, I owe you and Sue a dinner in Miami for your other "donations". Looking forward to it. What night is good for you?

  2. #12
    Gold Member Gold Member Full Force's Avatar
    My Boats:
    85 Cigarette Mistress
    Join Date
    Oct 2005
    Olmsted Falls,Ohio Marblehead,Oh
    Quote Originally Posted by carm View Post
    Can you recommend a cam (specs) and intake?
    With my combo most are telling me that my stock 420 cam is a good cam and to stick with it, I will be contacting a cam builder here soon before I finalize my choice, with the 330 deal, same goes, i would have to think a stock 420 cam would work good for a set lets say Edelbrock ovals or even a iron rectangle, the 420 cam is on a 112, 228/236@.50 and I think .530/.550 lift, I will look up specs here soon.
    85 Cigarette Mistress
    86 Baja 320 Force R.I.P.

  3. #13
    Registered User
    My Boats:
    just a baja and a 12' Jon Boat with Twins
    Join Date
    Feb 2005
    St. louis, East Sider
    I thought the 89 330's are still 2 bolt mains, but maybe I am wrong.

  4. #14
    Charter Member #927 Charter Member Payton's Avatar
    My Boats:
    1991 34' Super Hawaii
    Join Date
    Jan 2001
    I believe the Crane 241 is a slight improvement over the Merc 420 cam. That is unless you want to bump up to full Hydr. roller.

  5. #15
    Charter Member # 55 Charter Member Griff's Avatar
    My Boats:
    ..........32........... Active Thunder
    Join Date
    Oct 2000
    The 420/525SC/Crane #132561 cam is .530/.551, 228/236, 114 lob sep.

    Very similar and less expennsive cam that will make the same HP is the Crane #134241. Its .534/.553, 226/236 112 lob sep.

    I would use an Edelbrock Air Gap intake manifold and Holley 750 carbs.

    Upgrade exhaust to some Revolution Marines.

    Thats about as low budget as you'll getand still see probably a 5 mph gain on top.
    Last edited by Griff; 02-05-2008 at 10:38 PM.

  6. #16
    My Boats:
    24 Skater, 292 SR-1 Formula, 382 Fastech, 41 PC
    Join Date
    Apr 2006
    Grand Lake (E-Dock Junior Varsity)
    ive done all the research for this same project and decided to just sell mine outright when i get ready for the project and just buy 502's. When they sell, the cost of the 502's wont be anymore than TRYING to squeeze the power I want out of the 454's and its still merc power and i didnt kill the resale to awful bad..

  7. #17
    Registered tomcat's Avatar
    Join Date
    Feb 2001

    This brings back the memories. Here is what you are up against.

    Heavy boat means you don't want to change prop pitch, you need the current pitch to get on plane. Cast pistons say no to supercharging. Can't raise compression much and stay on regular gas.

    So to increase power and speed you are left with the option of raising RPM. Because it's a boat let's say 5200 maximum. That means you need a better intake manifold, better heads, bigger cam and better exhaust.

    Intake is easy - Edelbrock RPM air gap, dual plane because of the weight of your boat

    Bigger cam - something like the Merc 420, get the complete cam kit to handle the higher RPM

    Better exhaust - if the boat has log manifolds get a set of Merc centre risers from someone who bought aftermarket. The centre riser flows much better than the log manifolds and the weight of cast iron isn't going to make any difference on your boat. You can also buy an aftermarket elbow that will improve flow.

    The money you save by not buying aftermarket exhaust is going towards...

    Better cylinder heads - small port, good low and mid lift flow numbers, sneak the compression ratio up a bit. So many choices here starting with the Edelbrock or GM oval port head with 110 cc chambers

    You could choose to use the cast iron GM rect port heads and spend your money on aftermarket exhaust. That way you have essentiallly built a Merc 420. But you have built the engine around heads which are a bottle neck for further development.

    Starting with better heads and centre riser exhaust should make the same HP but then it's easy to add the aftermarket exhaust for more power later on without tearing the engine apart. And believe me you will want more HP later on.

    Some will say you can improve stock iron heads a lot with proper porting. It's true, extensively modified small peanut port heads have made 600 HP on 540 CID (Lingenfelter). You just have to compare the cost of good aluminum heads out of the box to the cost of porting iron heads and decide from there.

    What's all this going to get you? If you are spinning a 21P prop at 4600 RPM to get 55 mph, spinning the same prop at 5200 RPM will get you 62 mph. It will take 420 HP to achieve this increase in speed, so the engine changes match the hull requirement.

    If you think this is a lot of work for 90 HP and 7 mph you're right, but these are the easiest gains you will ever get in a powerboat.

    Good luck with your project, we've all been there.


    P.S. If you're curious about the next phase of this disease... you sell the 454s and buy 502s with aluminum heads. Then you stroke them to 540s. Then you add superchargers. Along the way you break a lot of drives. Then you upgrade to Konrads. Not sure what comes after that...

  8. #18
    My Boats:
    1987 Donzi 22; 2008 Donzi 28 ZXO
    Join Date
    Feb 2006
    Tallahassee, FL
    Quote Originally Posted by 320es View Post
    I thought the 89 330's are still 2 bolt mains, but maybe I am wrong.
    I'm with you. 2 bolt mains.

    I'd leave everything alone and run the piss out of it. The most I'd do is a mild cam upgrade to get you into the 350 range, I wouldn't go much more than that power wise unless you have budget to do the whole thing over, bottom up.

  9. #19
    Platinum Member Platinum Member KAAMA's Avatar
    My Boats:
    A boat?....What boat??? How about a galvarnized warsh tub wit a toranady strapped own da rear!
    Join Date
    Oct 2000
    Western Michigan
    I have done a lot of research on upgrading/modifying the Merc 330hp engine since the early 1980's. And I have seen several people I know who had them modified back then as well.

    I will tell you of a friend of mine who had a 30' Scarab who I helped modify his pair of 330's. His 330's had 2-bolt main blocks. To begin with, we thought we needed 4-bolt mains for the mods we were doing until I found out otherwise. So, we kept the 2-bolt mains by just having the bolts replaced with studs and align honed the blocks. Money saved.

    Next, we were told that we could even use the stock CAST cranks....but to just make sure they were inspected, etc. We even had to turn them 10/10. We also kept the stock GM rods with the 3/8" rod bolts....only we added ARP rod bolts and had the rods shot peened and reconditioned. Money saved again. We DID go with a forged piston vs a cast or hyperutectic piston. We had the entired rotating assembly balanced. We modified the oval port GM heads with larger stainless valves, went to Holley 750cfm carbs, and switched from the GM cast iron pan cake intake manifolds to some aluminum dual plane hi-rise Edlebrock intake manifolds. The stock 330hp cam was replaced with an aftermarket hydraulic flat tappet cam and we added some Hardin P-1000 exhaust manifolds and tailpipes. We did not have the engines dyno tested, but with fresh engines and the same props our RPM's increased from about 4600-4700rpm to 5400-5500rpm.

    Many other offshore boaters in the area told us that without 4-bolt mains, forged cranks, 7/16" rods that we were going to blow our engines within minutes of planing off-----it never happened---heck, I don't suggest this, but he didn't even have oil coolers and just ran either Pennzoil or Valvoline straight 40w oil. Never had any problems with the engines for several hours/seasons until my friend finally sold the boat 6-7 years later.

    Had another friend do the same thing with his 330's in 1988. And I have seen several since then with great success including coaching my friend "Dyno" on modifying his 330's years back---but he did eventually go with forged steel cranks and some other higher grade parts.

    The real good one is the story about my cousin's 330 upgrade episode. He retained all his cast bottom end, just added ARP rod bolt, and he even still used CAST pistons. He modified some large oval port "truck" semi-open chamber heads with larger stainless valves, installed hardened seats, bowl/pocket/short side radius porting, 8.6comp ratio, aftermarket roller rocker arms, bore notch job, dual plane aluminum aftermarket intake manifold, Holley carbs, stock Merc Thunderbolt ignition, 32* timing, aftermarket flat tappet hydraulic cam 218*/226* .515"/.515" lift on 110* lobes with matching valve springs. On Tom Earhart's dyno it made 461hp @5100rpm and 510 ft lbs of torque @3600rpm or so with tubular style dyno headers, but he uses aftermarket GIL exhaust manifolds so he probably has lost about 20hp from the dyno. The engines are in his 32' Baja and picked up 10mph in his midrange cruising speed and does about 69-71mph or so at WOT on the GPS. Don't know if it is a ticking time bomb or not, but he did this several years ago with about 150-200 hours on it so far. Giddy Up!!!
    Last edited by KAAMA; 02-06-2008 at 03:11 PM.
    Thank God for the U.S. Marines!
    ...I'm still a student.

  10. #20
    Charter Member #655 Charter Member dyno's Avatar
    My Boats:
    1993 Sonic 31ss
    Join Date
    Dec 2000
    Holland, Michigan
    The stock heads and exhaust is the biggest limitting factor try to find some used Merlin ovals or some GM rectungular port heads first then dump the factory exhaust you can find alot of parts used on the board as people upgrade.You can make 500 hp with the stock block crank and rods I've done it, you can add to that as the funds allow. my .02
    If your boat has a sail do you ride a horse to the ramp?

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