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Thread: Why isn't it faster.

  1. #1
    jkh04200
    84 Chris Craft 186 Scorpion with a 228 merc. (305 cheby). I have completely restored the boat.
    Motor upgrades.
    Valve Job, and port work, bowls and matched the gaskets
    New cam, power range from idle to 5500
    shaved heads and intake .060, should have put comp at about 9.5
    1.7 roller rockers
    T/T exhaust
    Heads and cam were done/chosen by a "performance guru" 30yrs exp.
    I should be somewhere in the 300hp range from what I was told.
    50GPS at 4700 and the boat only weighs, by the book, 1500#
    18.4" long 7' beam
    Buddies 1979 Chapparell 198 with same motor/drive, diffrent cam, but 19.6" long with an 8' beam 2700# 56GPS

  2. #2
    jkh04200
    Also I do have WOT and timing is set at 10 intitial 34 total. I know there is alot that can be done with fine tuning but it seems to me I'm way off to start with. One thing that has been in the back of my mind is. Could shaving the intake messed up the "not that great" of flow characteristics even more?

  3. #3
    Jim W
    A GPS will humble most boat owners......
    Be good, Jim

  4. #4
    cfm
    Need info on cam / intake / carb and head casting #'s.
    I would bet your boat is in mid 2000lb area. 1500 might be without engine/drive.
    Are you sure about 1.7 rockers ? Most SBC are 1.5 or 1.6
    =================
    What's your drive gear ratio ? What prop and pitch do you have ?

  5. #5
    jkh04200
    I understand bout the GPS.
    My boat is over a thousand #'s lighter and 50 plus HP more than my buddies. Thats what i don't understand.
    Both boths are the same style, runabouts with open bows. Hulls are the same basic design.

  6. #6
    DelawareDave
    Comparing your boat to your friend's boat is kind of like comparing apples to oranges. 4700 WOT sounds a little high. Not for sure exactly, but I believe max WOT for that motor is 4200. What pitch prop and what ratio drive do you have? Is the boat bottom painted?
    And to be perfectly honest with you, I don't expect you will see a lot more top speed with that boat/engine combo.

  7. #7
    jkh04200
    Comp Cam. Lift. .433I, .424E
    Dur. 206I, .212E @ 50
    Q-jet with stock intake and heads.
    I'm sorry 1.6 rockers

  8. #8
    jkh04200
    I understand about the comparison but they are the same style of boat. Its not like I'm comparing to a baja or some other style "go-fast". No the bottom is not painted. The WOT rpm is 42-46. The prop is a 17p Mirage plus. I know I need more. But, at about 500.00 a pop i don't want to buy a new prop until I'm sure what I need. Going to a 19 will pick up, what. 2 MPH. But going up in prop is also gonna reduce RPM. I would think with a 17 I'd be hitting alot more RPM. Not that I want to. Its just a solid indicator. As i said earlier, and I understand its kind hard to cmpare, my buddy has less HP and is already 6 mph faster.

  9. #9
    Infomaniac
    Give it some more timing.
    But... boat going fast is not all engine.

  10. #10
    SnoC653
    If you're hitting WOT and reaching redline it's not the engine you should be looking at. You either don't have as much prop, gears, redline rpm, or have more slip. Is he maxing at 4600 RPM also? If you go up in prop and can still max your RPM try more pitch yet. Once you hit WOT RPM drop you'll know the biggest prop you can spin. Or change the gears and spin the prop faster and you can get to the same thing. But it doesn't sound like an engine problem to me.

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