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Thread: Anyone wanna give it a shot?

  1. #1
    clownpuncher
    I've got a friend ....
    Lets say he's got a heavy 21 foot v-hull jet. Damn near 4,500 pounds worth of boat and "stuff"
    Pump is a Berk 12jg with a Mag Bronze Legend a/b ( I believe this is equal to a Berk A)
    Set-back, inducer, droop, yada yada yada
    The old motor dyno'd 613hp on a Super Flow and spun the pump at 6400 rpm
    The new motor makes 700 hp at 7000 rpm
    670 ft lbs at 5200
    These numbers came off of a DTS dyno at 98 degrees room temp and shitty barometrics.
    Any pump gurus wanna give an opinion on what impeller would best suit a boat like this? For my friend
    Intersted in hearing all aspects.
    Thanks in advance
    ROC

  2. #2
    ck7684
    I'm no guru by any means, but what more important, hole shot or top end? Have a graph of engine output throughout the RPM range? How was the performance with the previous engine? An "A" (berk size) sounds good to me, but like I said, I'm no guru...

  3. #3
    clownpuncher
    I do have a graph. Lemme see if I can scan it.
    Boat ran well on the old motor, till it broke after 60 hours.
    A boatload of people, gas and cooler would get me to mid 70's. Holeshot was nice, but, not a drag boat launch by any means. Great mid range punch.
    Old motor peaked on torque at 3400 rpm.
    New motor is way better, parts, build etc. Love my new builder, great guys. They actually drag race in Pro Street, build, R and D all their stuff. Very impressive shop.
    I'm gonna run the boat with the current impeller tomorrow at the river and see what she does.

  4. #4
    VAMI
    I would think a B minus. are you sure the old engine made peak tq at 3400??????? and made 617 hp.That engine would have 950 ft lbs at 3400 to make 617 ( peak tq times that rpm) divided by 5252 = hp

  5. #5
    clownpuncher
    . are you sure the old engine made peak tq at 3400??????? and made 617 hp.That engine would have 950 ft lbs at 3400 to make 617 ( peak tq times that rpm) divided by 5252 = hp
    Good catch. Make that a peak of 614 ft lbs at 3900 and supposedly 613 hp at 6400, per the dyno sheet.
    I'm not too confident in the old dyno sheet. It shows too much fluctuation at the top. Whatever, live and learn who to trust.
    Thanks for the reply.

  6. #6
    clownpuncher
    BTW, all the info I gather here is for my own info/knowledge/learning as I boat around and take mental notes of what peoples opinions were. I figure any day you learn something new, it's a good day.
    Rather than make my own changes, I'm gonna leave that to the pros in the off season, which is right around the corner

  7. #7
    Senior Member
    Join Date
    Apr 2010
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    2,920
    I figure any day you learn something new, it's a good day.
    Words to live by! I couldn't agree more.

  8. #8
    502 JET
    I'm no expert but I'll add my .02.
    The engine is built for a drag car not a jet boat. The cam is wrong. 7000 rpms is too high. That's why a B- impeller was suggested above. It may let you hit 7k rpms but it wouldn't move that big boat too efficiently.
    How many rpms could turn with the old motor?

  9. #9
    revndave
    My.02 You need a AA impeller for those big boats

  10. #10
    MikeF
    The old motor dyno'd 613hp on a Super Flow and spun the pump at 6400 rpm
    The new motor makes 700 hp at 7000 rpm
    670 ft lbs at 5200
    Should have fixed the pump.:devil:
    You'd need at least 860+ hp to turn that impeller at 6400rpm. The boat and or pump has issues.
    New motor ok w/ same impeller and a tighter pump (but no advantage over original engine.)......Doh!

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