SBC Jet build
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SBC Jet build

  1. #1
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    Default SBC Jet build

    My goal is to have the fastest boat around, excepting the blowers.
    Plan is: Have a 18' Wriedt. Very light boat and I'm told it will easily do 70mph. I want to try for 80. Dangerous I know but I'm 66 and don't care.
    Using a 400 4bm sbc with a 327 crank. Offy tripower w/2GC's-capacity of 975 CFM, Brodix heads about 64 cc to make 10:1 & use pump gas, KB flat top hper. pistons, Eagle rods, Crower hyd. roller about .500 & .535 lift and about 220 duration with a large lobe seperation, 1.5 roller rockers w/ locks, roller chain with lock and button & 3" thru transom. I found what looks like some old real efficient looking hump type cast iron headders and riser, they look more free flowing than the Glenwood logs. Expect to scream 5,500-6,000 rpm regular with a Berkely 'C' impeller and stuffer grate. Large capicity oil pan, oil cooler, main cap stud girdle and cam girdle.
    Because it's a sb may be able to keep it all in the box and make a playpen on top. Velocity yellow with white graphics & matching interior, named "Mongoose".
    I'll only have a few thousand dollars in the engine. I figure that set up will stay together up to 6,000 rpm. Completely stock it's rated at 5,500!
    I am open to suggestions as to improvements in speed. No, the the tri power and flat tops are mandatory. Even with it's flow problems it's still better than an 850 Holley, and I can run the 2bbl all day up to 4,000 on a tank of gas. And when I want more power I still have the equivelent of a 700 cfm 4bbl to kick in. Has anyone ever seen a tripower sb jet? If I can keep it all in the box, it'll be a sleeper until I start it up. It won't idle nice and the wot sound of a tri power gives goose bumps. The flat top is the most efficient piston for the sbc.

    Mongoose

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  3. #2
    Senior Member HBInHeat's Avatar
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    only thing ur guna be faster than is a pontoon boat. is this a joke or what

  4. #3
    Senior Member jyeager's Avatar
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    ^ lol

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  6. #4
    small block jet 2sangers's Avatar
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    Default small block jet

    Dude, you are kidding right? Don't go giving us real small block jet owners a bad rep.

  7. #5
    Senior Member Futs's Avatar
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    Quote Originally Posted by 2sangers View Post
    Dude, you are kidding right? Don't go giving us real small block jet owners a bad rep.
    What do mean by real?? A small block is a small block. I think his idea is bad ass. Kinda going for the retro old school look and have a little somthing to have "FUN" with. Not everybody wants a race boat...hes 66 years old. Few parts i would of chose to upgrade, but all in all...his choice.

    I find that he wants the fastest thing out there to be funny, but that could be an attempt at a real shitty joke...hahaha

    Post pics up. Lets see the engine and the hull Mongoose

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    Hey, lets not rain on this guy's parade. He might build the fastest jet boat around... It just depends on where 'around' is... If it were me, I'd skip the 327 crank and go with the 3.75" 400 crank. With a .030" overbore he will have a 406 cid engine. I'd also go for some serious lift and duration on that cam, like 254* on the intake and 266* on the exhaust (at .050 of course) and .600 or more lift and roller lifters... With the Brodex heads this will make over 500 hp even with flat top pistons... This will not cost anymore than the engine he proposed. I have a lot of experience with this combo and I can tell you it works. Remember, there is no replacement for displacement (NA that is) and this is especially true in a jet boat...

    And if you want a real serious small block, go with an LS engine like I did in my Comp Jet...

    Shirl
    CJ60

  9. #7
    Senior Member DuaneHTP's Avatar
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    Maybe on the engine, but in a "18' Wriedt" jet boat???? Come on.

    Duane HTP

  10. #8
    Senior Member jetboatperformance's Avatar
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    I have to agree with Duane re this particular Hull (no offense) , it (the Hull) will probably benefit from a serious weight loss program to help to SBC make it move out , I will say Josh and I have produced a few hard running small block jet boats over the years , cant say they were cheap (to make the power) and I'll admit two of three were 16' Two ran 80 the 18' ran 65ish You go Mongoose have fun with this More power to ya !




  11. #9
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    Default Jet boat build

    Hey guys, thanks for the comments. Like you, I'll still be around for a while.
    Sorry for the misconseption. I think I stumbeled into a swarm of race boat type boat people. I'm not there.
    Yes I want the retro look. It's an outrageous boat design. No one else will have one like mine on the Colorado between Parker and Davis dams. This is to be a fast, fun boat. If it's not fast enough as I plan, I'll put a blower on it. I don't mind spending the money if it does what I want and I'll burn this boat to the waterline if it doesn't. I'll get back when I find out what it does.
    Sorry to hear only a few of you can envision what I plan to be a good idea. We didn't get to the moon by thinking we can't get there. If it's a failure I'm not afraid to tell y'all, but I'm gonna try.
    Crower said that's the biggest hyd. roller cam I can use with the wet thru transom; any more lift and over 220 it will suck water. Those who think otherwise please tell me why.
    Mods y'all missed is to blueprint the bottom, of course blueprint, clearance and balance, and a ride shoe, experiment with nozzle sizes, and an ss impeller.
    I have no intention of embarrasing sb's. What makes everybody think this boat will be slow? It's the 'Spoiler' model, only 15' at the water line docked. Don't know the exact weight yet. It ran new with a 455 at 70. I tried to lift it at the corners and it's lighter than my Hallet flattie.
    The 327 crank was an idea. I particulary like 327's; and when I found out that the lg. journal crank will fit into a 400, the idea was borne years ago. If y'all like to bore 350's, how 'bout boring a 327 to 4.155? A short stroke large bore. It calculates to almost 350ci.
    The circle of a 3.25 is 10.2, of a 3.48 is 10.9, and 3.75 is 11.7. Figuring the counter weights to be the same weight for all, it works out this way. The differecce between the exremes of the two strokes is about 1-3/4 inches. Therefore you have to swing all that weight on the heaviest part of the crank 10 miles an hour faster to get the same 6000 rpm. Without doing the force needed to move that mass at 6,000 y'all know that's a lot of hp just to move the bigger crank. I rather the hp to go into the impeller. Simply, the 327 crank engine revs. quicker than a 3.48 or 3.75 stroke: and it's all about getting there first. My theory here is, that because of the light boat, I don't need torque, I need hp. I figure my motor to be about 450.
    I plan on using the motor box. A shame to hide the tripower. That's still a consideration, but I'm convinced that the tripower will do what I want. Been looking a long time for USCGA flame arrestors that will work on the tripower. Just found 9X4 K&N's yesterday.
    I'm not discouraged by the less than enthaustic comments. I realize that I'm probably the only one who has ever tried this combo. and will keep a humble attitued, but I'm still looking for suggestions for more speed, hp. When I can't find any more improvements, I'll start putting it together. Got half the parts already.

    Mongoose

  12. #10
    Senior Member Mojave85's Avatar
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    Well - you have certainly put a lot of thought into this! Sounds like you have your mind set on this set up so go for it. Good luck!

  13. #11
    Senior Member DuaneHTP's Avatar
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    Read your PM.

    Duane HTP

  14. #12
    small block jet 2sangers's Avatar
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    Default small block

    Ok, I thought you were joking around at first but I re read your post and see that you only want to run around 80. I personally would stick with the 406 so you don't have to run a C impeller and turn a lot of rpm. I have run N/A 406's in 18 foot jets with an A impeller and been close to your goal. I currently run a blown 406 in my 21 foot daytona and have surpassed the 80 mph mark, Good luck with your project and remember light is fast.
    We race a very light Sunkisst tunnel which ran 114.8 at Augusta with a nitros assisted small block.

  15. #13
    Platinum Member BigSteve's Avatar
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    I don't need torque, I need hp. I figure my motor to be about 450.
    I plan on using the motor box. A shame to hide the tripower.


    Mongoose[/QUOTE]

    The motor your buliding would be great in a Rat Rod, I have run a 440 6-pac nice for the street

    However, a boat needs torque. So you need those Cubes to make torque to turn that pump

    I would go BBC,you will be happy you did lots of deals out there
    If you ain't the lead dog the view is always the same !

  16. #14
    northern member Canuc's Avatar
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    something a little fishy with this thread but if that's what you have go for it and have fun, sounds like you have it all fiqured so what are you lookin for info on ? the cast stern-drive ex. and the 283 carb "won't idle nice" with a mild wide lsa cam
    Quote Originally Posted by gn7 If your ran a cammer your odds of finishing WERE ZERO.

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