New to Jet Boats, need motor combination help
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New to Jet Boats, need motor combination help

  1. #1
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    Default New to Jet Boats, need motor combination help

    Good day Gentlemen,

    I am new to jet boats, but I am not new to boating or working on vehicles.
    I picked up a 78 miller 20' boat with a Berkley JC pump and assuming an A impeller. It has cast log manifolds and although I am open to buying some tubular headers, they gotta be through transom. I boat in a busy area with lots of cops.

    Its a major project boat, it was setup for a BBC and I intend to run a BBC again.

    I have a 454 short block and otherwise I have nothing else on the motor.
    The motor is a 2 bolt block with a stock crank and rods, and wiseco domed pistons (I will find out the exact dome, but I think 21cc), ARP main studs and APR rod bolts.

    The motor clearances were machined on the looser side (it was gonna go into a weekend car). I will measure everything to find out exact main/rod bearing clearances and piston to bore clearance.

    I would like to build this boat to be a fun boat for me, less so a family boat (got one of those), just for me and my buddies to have some fun with.

    I need advice on everything lol, but most important right now I need advice on what I should run for bearing/bore clearances, and what kind of top end to purchase to complete this motor.

    From what I understand I need to make as much torque as possible (wish it was a stroker but its not). I have some old BBC parts from a Solid Roller motor including Eddy heads, but a friend of mine is interested in those so for the sake of this build I am gonna say I have nothing but the short block.

    I am open to buying aluminum heads and even a solid roller setup. I was thinking I could possibly run a roots blower as well with some big chamber heads, but that might be pushing it too far for this project.

    Edelbrock has some marine heads with 110cc chambers but they require custom pistons which means I can't even use my new short block.

    Any other recommendations? Any opinions against a solid roller? In my experience with them they perform very well everywhere, not just high RPM. I have no problem setting valves.

    Let me know what you guys think and which way I should lean. Remember a weekend boat to have some fun and hopefully get decent MPH. My budget isn't too tight..

    Thanks

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  3. #2
    Senior Member jetboatperformance's Avatar
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    Default Welcome to the jet boat boards

    Welcome the Jet boat boards !

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    Senior Member jms-1's Avatar
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    Welcome, lets see the Miller, we like pics...

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  6. #4
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    Welcome. You might do a search. There just recently was a pretty good thread on two bolt bbc blocks. If you are going to stay with the two bolt block, you probably can make all of the power it will reliably live with using a good set of oval port heads and a hydraulic cam. Just my .02, not sure I would invest in aluminum heads if I was going to stay with the two bolt block and stock crank.

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    Quote Originally Posted by fastmarlene View Post
    Welcome. You might do a search. There just recently was a pretty good thread on two bolt bbc blocks. If you are going to stay with the two bolt block, you probably can make all of the power it will reliably live with using a good set of oval port heads and a hydraulic cam. Just my .02, not sure I would invest in aluminum heads if I was going to stay with the two bolt block and stock crank.
    Hey guys,

    I have been away traveling for work right after I got the boat, so I have no pics to post, but I will when I get back.
    I have spent hours and hours searching and I'm not any further then I was.
    Everyone says search on forums and yet most guys do nothing but search and search for days before posting. Trouble is there is too much info on the forums and way too many different opinions. Usually you can get the basic info out of the searches, but its still difficult if you are a newb to the topic searched.

    I maybe failed to mention, I live in Alberta, Canada. We have high altitude here so cars and boats alike perform less here. Lower HP and usually lower MPH and RPM achieved with same combos.

    I have money to spend I am just trying not to dump a pile of cash into the wrong setup.

    SO for the sake of this build maybe I should ask a different question.

    Who has a 454-468 bbc combo in a 19'-20' jet boat with a JC pump and A impeller, and what your combo is and what do you run? Do you like it and what would you change?

    Here is what my days of searching got me for knowledge so far (correct me if I am wrong):

    -#1 Jet boats operate at RPM. So the target RPM is important for motor setup. Anything else is less important.
    -#2 use marine distributors, marine carburetors
    -#3 aluminum heads should be marine grade (although I am not quite understanding why. My boat will be used fresh water only, not too much (Canada here and stored indoors)
    -#4 seems that cold lake water cooling is not an issue, so perhaps cast iron heads can handle a bit more compression then lets say a car?? (am I wrong)?
    -#5 use of roots blowers or tunnel rams is cool, just expensive. I have been reading up on weiand 177 blower. Single carb. 3.5lbs of boost. I think with one of these my motor performance would equal a similar non boosted motor at lower altitude. But is this blower too small for a 468? Whats the max compression I can run on a jet boat (iron or aluminum heads)? to safely use one of these blowers?
    -#6 run quality oil, oil cooler and proper clearances (still can't find a solid answer on what those should be for a motor similar to mine)

    I would like to stay away from dual carburetor setups for expense and complexity, but if its gonna make a reasonable difference i would be willing.
    What about single plan intakes with a tall spacer? Would it help build velocity and intake volume similar to TR but less complex?

    Seems to me that a decent setup would be rebuild the 781 heads I have with some bowl work (I can do this work myself) using decent valves (any recommendation on what valves) and proper valve guide clearance (again any suggestion?) with a solid roller setup, a tall single plane intake with a tall spacer and a 750+ marine carb.
    I would like aluminum heads for added power, reduced weight and possibility of smaller combustion chamber so I can build compression but not so sure which heads would be a good combo for my "less then optimal" 2 bolt main block and stock crank.

    I like solid roller cams because its not the 70s anymore, and flat tappepts don't make the same power anywhere as SR. Hyrdo rollers are OK for this application, but valvetrain will be heavier and will probably leave some power on the table.

    If I expect to turn 4500-5000 rpm (which is what I expect, am I wrong? 20' JC pump A impeller 454 5000ft altitude), should i try and setup this motor to make peak HP around this RPM or peak torque?

    What about use of nitrous in jet boats. Small shots for acceleration? I haven't had a chance to read much on this. I use nitrous on my cars all the time.

    Sorry for the rant guys just trying to filter out all my days of searching.

    Thanks so much for ANY suggestions or comments.

  8. #6
    Senior Member jms-1's Avatar
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    Just to give you an idea, my 19' miller would run right at 70mph (gps) @5000 rpm with a tired but well built 427 and a stock jc pump A impeller with place diverter. It ran ok for what it was.
    You might want to ask the engine questions in the '' on the dyno '' section. there are some very savy people that hang out there and don't pay much attention to Jet section very much.
    Last edited by jms-1; 02-12-2013 at 07:06 PM.

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    Quote Originally Posted by jms-1 View Post
    Just to give you an idea, my 19' miller would run right at 70mph (gps) @5000 rpm with a tired but well built 427 and a stock jc pump A impeller with place diverter. It ran ok for what it was.
    You might want to ask the engine questions in the '' on the dyno '' section. there are some very savy people that hang out there and don't pay much attention to Jet section very much.
    Thanks for your reply.

    I'll try and search a bit more and post on "on the dyno" section.

    5000rpm @ 70mph tells me where I need to be.

    Any idea what heads/top end you have?

    Thanks again

  10. #8
    Senior Member jms-1's Avatar
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    The 427 had about 12-1 comp, ''074'' GM winters rectangle port heads, old style weiand tunnel ram with 2 800 cfm Holley's , the cam was a comp xm288h hyd flat tappet, Bassett headers. This was in the boat when i got it, I felt it ran good but wasn't the best selection of parts for a Jet. Now i am building a pump gas 496 with Profiler 290 oval port heads and it will be getting a custom solid roller cam after the heads get some work and spend a little time on a flow bench . I will still be running the same intake and carbs . You might want to think about spending a little extra cash and get a custom grind cam that is built for your engine specs. I hope this helps.

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    Quote Originally Posted by jms-1 View Post
    The 427 had about 12-1 comp, ''074'' GM winters rectangle port heads, old style weiand tunnel ram with 2 800 cfm Holley's , the cam was a comp xm288h hyd flat tappet, Bassett headers. This was in the boat when i got it, I felt it ran good but wasn't the best selection of parts for a Jet. Now i am building a pump gas 496 with Profiler 290 oval port heads and it will be getting a custom solid roller cam after the heads get some work and spend a little time on a flow bench . I will still be running the same intake and carbs . You might want to think about spending a little extra cash and get a custom grind cam that is built for your engine specs. I hope this helps.
    Yes that helps. Thank you.

    I think I am going to run my 468 with 781 heads, minor bowl work and a solid roller setup.

    Run it with a dual plane or a single plane (haven't decided yet) with a spacer and a marine 850 carb.

    Should be able to use most of my parts and get me on the water. Test the boat and pump out and go from there.

    I have a nitrous kit sitting around too, so when time comes to build a better motor, I can try to see how spray works as well...

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    Quote Originally Posted by Igor View Post
    Yes that helps. Thank you.

    I think I am going to run my 468 with 781 heads, minor bowl work and a solid roller setup.

    Run it with a dual plane or a single plane (haven't decided yet) with a spacer and a marine 850 carb.

    Should be able to use most of my parts and get me on the water. Test the boat and pump out and go from there.

    I have a nitrous kit sitting around too, so when time comes to build a better motor, I can try to see how spray works as well...
    What valves would you guys recommend running with BBC in a jet boat? type? Was gonna run 2.19/1.88s for size

  13. #11
    Senior Member Alter Ego's Avatar
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    I am by far no expert, but I'm runnin a 505 two bolt, studded, eagle crank and h beam rods 13:1 comp procomp aluminum heads (yes all you haters I know you think they are junk lol) 711 custom Solid roller by Chris Straub, single plane intake and a 1050 dominator, I spray 100-250 however I am feeling that weekend, but I'm not a motor genius so I can't help with tolerances and other specifics. My ( pretty heavy) tx-19 runs 102 in the 100+ degree humid arkansas heat on a 150 shot, bout 92-93 on motor. Welcome to the boards and please post up pics!
    2011 Rouse Performance 19'

    WFL Crew

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    I have a 2 bolt 468 with stock crank and rods 9-9.5:1 compression. A pretty mellow hyd roller cam .566 lift. 781 heads with oversized valves with some mild port work. Mine is in an 18' gullwing with an A impeller. It spins 5250 at 4600' elevation. That's with a single 850 dp. About 71 mph.

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    Quote Originally Posted by mrjoshua View Post
    I have a 2 bolt 468 with stock crank and rods 9-9.5:1 compression. A pretty mellow hyd roller cam .566 lift. 781 heads with oversized valves with some mild port work. Mine is in an 18' gullwing with an A impeller. It spins 5250 at 4600' elevation. That's with a single 850 dp. About 71 mph.
    Awesome! Thanks for that info. If you don't mind me asking, what kind of intake are you running?

    Thanks

  16. #14
    The Good mrjoshua's Avatar
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    Dominator with a tapered shoe. 1/8th +/- above keel. Nothing at all aggressive. Need to switch to a back cut for more lift.

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