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Thread: Proper impeller for 21' Ultra

  1. #1
    Hey guys, I'm new to owning a Jet boat and really enjoying everything. I have a question about the impeller I should run. Right now I have a 21' Ultra with a marine power 454 that puts out about 330hp. I'm not looking to drag but right now the boat runs 50mph at 4900rpm. I'm looking to get a few MPH more out of the thing without killing the possibility of pulling skiers, and hopefully not making it drink too much more fuel ! I'm not too sure what impeller it's running now, I'd guess a B or C from the chart that the pump came with when I compare the hp/rpm I'm running. Thanks for any help!!!

  2. #2
    Before you do anything, check the tach! If you can't find a good checker, then borrow a MSD 6AL box and a 5000 chip, see if the cutoff rpm agrees with the tach(the MSDs are quite accurate in the limit function). It is more likely that the tach is off or the pump is worn out than a B or C impeller was installed, but anything is possible. TIMINATOR

  3. #3
    I'll do that next weekend when I'm back out there. I doubt the pump is bad, the boat only had 18 hours on it when I bought it - and the paperwork from Ultra for his test drive states a 50mph hull speed.

  4. #4
    How hard is it to pull the pump apart to see what impeller I'm currently running? It looks pretty simple, but I don't want to pull it apart and end up with a puzzle.
    Thanks again

  5. #5
    How hard is it to pull the pump apart to see what impeller I'm currently running? It looks pretty simple, but I don't want to pull it apart and end up with a puzzle.
    Thanks again
    You haven't lived until you've pulled something apart and had to sit there with a six pack and a retarded look on your face for 3 hours trying to figure out how it goes back together!
    It is as easy as it looks. Pull that sumbitch apart!
    Or you could just look at the tag on the top/front of the jet pump and it will tell you what impeller was originally installed in least my pump has that punched metal tag on it.

  6. #6
    Great, thanks for the tip - I'll check for the tag first and if it's not there I'll be sure I've got at least a 6 pack in the cooler!

  7. #7
    330HP and 4900 RPM, sounds like the "A" I'm running. My 454 used to be 330 HP and turned 4850 to 4900 solidly. Your speed trouble is that 21 feet of 'glass. I am running mid 60's with an 18'er, 70+ on 150 more N20-HP. If you want to reach 6o's, I'm suspecting you will need arround 450 HP, less perhaps if you have a place-diverter/jetovator to trim the nozzle up to help carry the bow off the water. Maybe then only arround 400HP (assuming your 50 is without a diverter now).

  8. #8
    That's my other thought, it's not exactly light... I do have a diverter and also a drop nozzle on it. If 50's all I should be running with the 330hp I can deal with that, that's actually a little quicker than I normally run up and down the strip, I know there's no way I'm gonna compeat with the 18' boats out there - I just want to be sure some dude in a bayliner wont be able to keep up

  9. #9
    Better find some more HP then .......... I have a friend whose Cobalt 502 runs 64 flat out.

  10. #10
    More seriously, it's my understanding that the droop nozzles actually add weight to the nose (they are supposed to lift the stern). BAD effect for speed. Maybe a straight nozzle would help as well. Save the trim fighting the droop's effects.

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