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Thread: GK 1390 speed?

  1. #1
    OCFZR's Avatar
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    GK 1390 speed?

    I have a GK 91 octane BB kit with 15 hours and cannot get over 70 mph even with 1/4 of a tank. I am running 7160 hot rpm's with the Group k 14/20 concord. I'm using a R&d plate, 1200 grate, and R&D tabs. I need to get to at least 75 mph and I know I should be running at least 72 with this kit.

    Any suggestions?


  2. #2
    big83bronco's Avatar
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    this may be trivial and you may have already done this, but check your pump shoe. I was having a similiar problem with good RPM but no top speed. Mine was tearing out and dropping to low!

  3. #3
    Like a chimp with a ball-peen hammer smackwave's Avatar
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    Try swapping out the trim tabs and ride plate for the stock parts. I've gone back to the stock tabs with shims under them from the R&D flat bottom tabs and I'm quite happy. Check the impeller to liner clearance on your wear ring. What shape is your hull in, especially the keel? With the GroupK BBs going into older boats a lot of folks are being held back by hulls that have been beat to crap.

  4. #4
    OCFZR's Avatar
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    My hull is in very good condition and I have no cavitation. It's frustrating knowing that stock 05/06 are getting 70+ with just a dynafly and plate. I know I have significantly more power than them.

    Any other suggestions?

  5. #5
    GPRPITMAN's Avatar
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    Take a pic of the bottom of the boat ride plate pumpshoe area the rpm's and numbers don't jive you should be going faster

  6. #6
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    Boy I guess I should not complain. I've been working on the speed in the chops.

  7. #7
    philip_gpr's Avatar
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    some (most) of the R&D 1300 rideplates are terrible - the bottom has a huge dip

    you might check my comments on rideplate mods in this thread

    http://rivaforums.com/eve/ubb.x/a/tp...4/m/9511019071

    the rideplate properly modified gets you an extra 3 - 4 mph

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