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What next???

  1. #1
    AKA OhOneWS6 Last Mohican's Avatar
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    Default What next??? (Update 04-27-10)

    First off, Huge thanks to Tom @ Jet Boat Performance for the suggestion on the allen bolts. They worked perfectly as did the throttle bracket.

    I took the boat out this weekend and finally got rid of the dead spot at 3200 RPM. It was all a timing issue. Now I seem to have hit a brick wall at 4200 RPM and 51 MPH. I know there is more left in there. I'm just not sure where to look.

    Some questions:
    1) What MPH should I expect out of a Jacuzzi YJ pump at 4200 RPM?
    2) How much HP does it take to turn a YJ 4200 RPM?

    I am not looking to go super fast with this boat. I would like to see 60 - 65 MPH with the Pontiac motor.

    This is a very low budget project. Thanks to help from a lot of friends old and new, I am total out of pocket on this project ~$1000. I'm guessing that makes my $$$ per MPH ratio a hell of a lot better than most.


    TIA,
    Matt
    Last edited by Last Mohican; 04-27-2010 at 12:37 PM.

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  3. #2
    Boat Nut sleekcrafter's Avatar
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    verify the tach is correct, speeds in the ball park for 4200 small boat. Jacuuzzi pumps generally are easy to overpower in stock form. How about a little engine info for starters, c/r, carb size, intake manifold, exhaust type.
    Upper Midwest Power Boat Association
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  4. #3
    AKA OhOneWS6 Last Mohican's Avatar
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    18' SleekCraft Rebel. Speculation from KRE (Pontiac specialist) was ~425 HP. Holly 800 DP, Edelbrock Performer RPM, Hardin log exhaust with snails. Someone else started this build and the motor was already done so I have no idea on the CR. Engine specs below.

    Engine specs.
    -Pontiac 400 .030 over, Stock steel crank, Pontiac Super Duty Forged Rods, JE NHRA Forged Pistons
    -6X Heads
    -800cfm Holly double pumper w/1"spacer
    -Crower Cam-297HDP
    240/242 @ .050
    297/308 advertised
    .500/.500 lift
    112 l/s
    -Comp Roller Rockers
    -Comp chromoly pushrods
    -Comp lifters
    -Comp Double Roller Timing Set
    -ARP main studs
    -ARP rocker studs
    -SFI 12,000 rpm chrome balancer
    -Edelbrock Performer RPM intake
    -Glyptal paint lifter valley
    -High Torque Mini Starter

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  6. #4
    AKA OhOneWS6 Last Mohican's Avatar
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    :crickets:

    I'm kinda stunned. Not even the typical "ditch the and Pontiac" and "get the energizer kit" comments. I thought someone would at least know how much HP to spin that pump those RPM. If it takes 425 HP to spin that pump 4200 then I would know I have to look somewhere else.

    Anyone... Tom...

  7. #5
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    I think just looking at your parts and pieces that you're going to need 100-150 more HP to go 60-65 mph with your combination.

    I don't want to be the bearer of bad tidings, but I think your engine might be doing the best it can in it's present form.

    I think your at 350-400 real HP with your current deal. Just not enough in my opinion.

    RR

  8. #6
    Boat Nut sleekcrafter's Avatar
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    Don't know didley about Ponchos, so here goes.... I'd guess you have 1) a little too much duration in tha cam, some thing around 280 or so would suit you better. 2) and open plentum intake would suit the jet application better, dual plane imo serves no purpose, since there is no need for low end torque, below 3000 rpm, this may be a different case with the YJ Jacuzzi. 3) The 800 carb would be IMO to be a little too small, as well. A good 850 is hard to beat in the jet boat application. This is assuming the tune is good on the motor; timing, ignition system, and fuel system.
    Upper Midwest Power Boat Association
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  9. #7
    AKA OhOneWS6 Last Mohican's Avatar
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    Quote Originally Posted by RiverRacer View Post
    I think just looking at your parts and pieces that you're going to need 100-150 more HP to go 60-65 mph with your combination.

    I don't want to be the bearer of bad tidings, but I think your engine might be doing the best it can in it's present form.

    I think your at 350-400 real HP with your current deal. Just not enough in my opinion.

    RR
    First I want to say thanks for the input. Your not going to hurt my feelings on this deal at all. Like I said in my first post, $1000 for 51 MPH, my $$$ per MPH is better than most here. I'm am curious why you think 350 to 400 HP. Kaufman has been building Pontiacs for a long time. Most of the parts came from there on their recommendation. I would think their estimate would be close. Not disputing you at all. You may very well be right. Just wondering why you think the HP would be that low.

  10. #8
    AKA OhOneWS6 Last Mohican's Avatar
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    Quote Originally Posted by sleekcrafter View Post
    Don't know didley about Ponchos, so here goes.... I'd guess you have 1) a little too much duration in tha cam, some thing around 280 or so would suit you better. 2) and open plentum intake would suit the jet application better, dual plane imo serves no purpose, since there is no need for low end torque, below 3000 rpm, this may be a different case with the YJ Jacuzzi. 3) The 800 carb would be IMO to be a little too small, as well. A good 850 is hard to beat in the jet boat application. This is assuming the tune is good on the motor; timing, ignition system, and fuel system.
    Thanks Sleek. The one thing I noticed when I pulled the plugs was that 1,2,7,8 looked good. 3,4,5,6 looked lean. I was thinking the dual plain or the 1" spacer might have something to do with that. I may have another carb I can test with. A friend has a freshly rebuilt 850 with a new throttle plate just sitting on a shelf.

    The carb I have has had some work done at some point. I don't know the history but the choke horn has been shaved and the power valves removed. It looks to have been done professionally. It has a nice smooth finish on the surface where the horn was removed. That could mean jack chit though.

    Since it won't cost anything, I will borrow that 850 this weekend and see what happens.

    Any other suggestions?

  11. #9
    AKA OhOneWS6 Last Mohican's Avatar
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    Here is a little more info. Ignition is an HEI. Not sure where it came from but it is new. I put a new MSD cap and rotor (brass contacts). The wires are new 8mm spiral core. New plugs as well. I had a really bad flat spot ~3200 It would stumble so bad I really had to feather it to get past 3200. This was fixed completely with a curve kit and the lightest springs. Now when I floor it there is no hesitation and it spins up to 4200 almost instantly.

    Fuel pump is a new Holly blue. Holds ~6 PSI steady at WOT.

  12. #10
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    You say a spring kit helped the ignition problem at 3200, did you check the timing at high rpm (full advance), or only at idle (initial advance)?

    How does it act when you hit the wall at 4200? Additional throttle makes it bog down, or you have it wide open at that point?

  13. #11
    Seriously off center slowride's Avatar
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    I don't speak Pontiac, but here's a couple thoughts.
    I have a feeling you need a bit more initial advance. 4200 is real weak and barring something major (cam timing off, low compression, no secondaries) I would think you'd have more rpm especially with a YJ.
    By 460 standards, that cam has too much duration for as little lift as it has. The carb is ok if it's in good shape. I run 830 cfm at 5100 with a Stealth dual plane. Edelbrock says that manifold is good from 1500 to 6500 so I doubt that's the hold back.
    Check your timing, give it a couple degrees more and test it.

  14. #12
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    What is the secondary stamping on your heads (on the acc mount below the valve cover rail) normally -4 or -6 or -8)

    Some 6X's have huge chambers (near 100cc) and would result in pretty weak compression, even the smaller chambered ones are pretty "soft" for a 400

    For comparision my +040 400 in my sprint boat has a chamber volume around 50cc (smallest chamber head milled 080 !!!)

    See "in boat vid" post for my iron headed (class restriction) 400 Ponty

  15. #13
    Senior Member EVILFORCE's Avatar
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    I would not be surprised if you were not making 400 hp at that rpm. Loosen up your pump and get a few more rpm's and maybe get a little more hp.
    No Fool Like A Old Fool is there?

  16. #14
    Senior Member IRRebel's Avatar
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    I'm kinda with slowride on this. BUT, built many a hot rod Pontiac back in the day, and every one I ever put together liked single planes. Dunno why, or care, but they worked. Given your plug readings, you're seeing what I used to see regularly 15-20 years ago. Might well have sumpin to do with head design and why the REAL hot rod Ponchos (421-428 SD) had low rise single plane dual quads on them. (Pontiacs like high duratrion, smaller lift BTW. Built into their ports to increase atomization and velocity!)

    You're engine will be fine in a boat! Not gonna tell you to change it, lord knows we need more Pontiacs around. Slowride pointed you in the right direction with the timing. That is CRITICAL in a Pontiac. Not 1 or 2 degress off, has to be perfect! The HEI is NOT hurting you, it's fine.

    I would throw a couple degrees more intital advance on it, provided it doesn't exhibit starting, detonation, or idling issues. I'd also look seriously at your carb. You didn't specify what you had, but 850 is what I would recommend.

    Lastly, if none of these fix the RPM problem (I beleive you have enough HP to drive that pump with a pretty aggressive impeller), then it lies in the valve train. Springs mainly, but then you are experiencing valve float.

    Ray

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