What impeller cut should I get?
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What impeller cut should I get?

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    Default What impeller cut should I get?

    So I finally got my tahiti out on the water today and she ran great! But I'm not thrilled about the impeller cut that I have. I'm not sure what it is, but I think it's a Berkeley "C" cut. I'm running a 454 BBC with a Berk. 12JC pump. I was getting 47 mph out of the boat at 5,000 RPM. However, I was only getting 26-27 mph at 3800 RPM which seemed to be about where the engine was happiest running.

    So ideally I think I'd like to be cruising around 3200-3400 RPM in the low 30mph range, with my top RPM in the mid 4000s. I also wasn't getting a very good "holeshot" and the motor seemed to be lugging quite a bit until the boat got up on plane (which took a while). So I'm thinking maybe an "A" cut impeller? Or would I be better off with an "A/B" impeller cut?

    I'm hoping everyone here with the experience can point me in the right direction. Thanks in advance.

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    Senior Member gregb's Avatar
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    Really the best thing to do is start with the A cut. Try it out. If you want more RPM then have it cut to A/B, then B, etc. You can always have it cut down, you can't go the other way. I'd also check your tune and make sure the motor/engine is running well, if you indeed have a C cut impeller it should not be lugging the engine. How old is the jet, is this a new boat for you? Any history with it? Could be the jet needs a refresh.
    Last edited by gregb; 10-01-2017 at 09:12 AM.

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    Quote Originally Posted by gregb View Post
    Really the best thing to do is start with the A cut. Try it out. If you want more RPM then have it cut to A/B, then B, etc. You can always have it cut down, you can't go the other way. I'd also check your tune and make sure the motor/engine is running well, if you indeed have a C cut impeller it should not be lugging the engine. How old is the jet, is this a new boat for you? Any history with it? Could be the jet needs a refresh.
    Starting with an A cut sounds like a good place to start. But is it pricey to recut the impeller if I decide an A/B is the way to go?

    As far as the boat and jet, itís been my parents boat from the time I was born, but it hasnít been run or in the water for 10 years. This weekend was the first time in a decade it got wet. The engine seemed to run great, and ďluggingĒ is probably the wrong description for what Iím trying to describe.

    From a stop with the boat fully settled I was spooling up the engine to around 4500 rpm to get up on plane but there wasnít much oomph behind it. It would take a good 4-5 seconds to get on plane and then it seemed like there was better acceleration. It just seemed like the boat was working awfully hard to get going against the drag of the water. I remember it getting up on plane quickly before with the stock impeller.

    Iím planning on redoing the jet next spring, but still have no clue how much or how little to replace while itís torn down. At the very least Iím going to do the impeller.


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    Senior Member gregb's Avatar
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    I don't remember it being pricey to cut one down, but it's been a while. Itvcouod just be its worn out, too much clearance, or something of that nature. Where do you live, locals to you might have a preferred shop you can take the jet to, or that does that kind of machining. They aren't difficult to rebuild, but there are a few tools that you need main one being a puller to get the old impeller off. You should disassemble the jet first before ordering an impeller, usually the cut is stamped in the rearof the impeller. That will give you some info at least.

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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by 71BeaterBoat View Post
    So I finally got my tahiti out on the water today and she ran great! But I'm not thrilled about the impeller cut that I have. I'm not sure what it is, but I think it's a Berkeley "C" cut. I'm running a 454 BBC with a Berk. 12JC pump. I was getting 47 mph out of the boat at 5,000 RPM. However, I was only getting 26-27 mph at 3800 RPM which seemed to be about where the engine was happiest running.

    So ideally I think I'd like to be cruising around 3200-3400 RPM in the low 30mph range, with my top RPM in the mid 4000s. I also wasn't getting a very good "holeshot" and the motor seemed to be lugging quite a bit until the boat got up on plane (which took a while). So I'm thinking maybe an "A" cut impeller? Or would I be better off with an "A/B" impeller cut?

    I'm hoping everyone here with the experience can point me in the right direction. Thanks in advance.

    Beater boat you didn't say how big this Tahiti was (18/19/20 etc ?) or how it was loaded , However if its an 18' SK type boat for example , assuming your tach is accurate and the jet is in good condition internally , a moderate 450 HP BBC turning an Berkeley A impeller would be at approx. 4800 to 5000 rpms WOT , a "C" cut for example would produce significantly higher RPMS (approx 5400 + or-) given the same basic conitions Generally a "C" would not be a good choice for this application, and would be a worse choice if the boat was even larger (EG 21") Additionally under the scenario above (18' Tahiti 450 HP) the boat should be around 55 to 60+ MPH in decent water, near sea level, @ WOT

    * have you ever checked below the subfloor for water intermixed with the foam

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    Default What impeller cut should I get?

    Quote Originally Posted by jetboatperformance View Post
    Beater boat you didn't say how big this Tahiti was (18/19/20 etc ?) or how it was loaded , However if its an 18' SK type boat for example , assuming your tach is accurate and the jet is in good condition internally , a moderate 450 HP BBC turning an Berkeley A impeller would be at approx. 4800 to 5000 rpms WOT , a "C" cut for example would produce significantly higher RPMS (approx 5400 + or-) given the same basic conitions Generally a "C" would not be a good choice for this application, and would be a worse choice if the boat was even larger (EG 21") Additionally under the scenario above (18' Tahiti 450 HP) the boat should be around 55 to 60+ MPH in decent water, near sea level, @ WOT

    * have you ever checked below the subfloor for water intermixed with the foam
    This is an 18í Tahiti with a stock 2-bolt 454. Itís not the high performance 454 because it has the peanut ports (?). I have no idea what kind of horsepower this motor is making. It was loaded with 4 adults at sea level (SoCal). Most of the boat is stock as it was purchased back in the late 70s by my parents.

    The story with the impeller is that my dad felt like he was getting less pull from it in the mid 2000s, pulled it, and took it to a shop to get it replaced. The story he was told at the same was that they werenít making the same cut he had, and he was sold a ďbetterĒ cut. (He canít remember what the original was or what the replacement was. He thinks the original was an A/B cut.) But after replacing the impeller he noticed that his WOT rpm increased from around 4200 to a little over 5000 and he had a lot less power pulling skiers out of the water.

    Based on what Iíve learned recently thatís what leads me to believe he went from somewhere close to an A cut to a C cut, because of the big jump in RPM.

    Now that Iíve got the boat, my main goal is efficiency and motor longevity. A little more oomph out of the hole would be nice, but my daughters are young and I wonít be pulling heavy skiers or wakeboarders. Iím not too worried about top speed. I just want to be able to cruise around and keep up with the other boats in my family (30-35mph) without winding the engine out so much.


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    Senior Member jetboatperformance's Avatar
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    a C or even a B would not be an ideal IMO choice given that particular engine and where it makes power I would likley start with a AA or maybe an A

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    Quote Originally Posted by jetboatperformance View Post
    a C or even a B would not be an ideal IMO choice given that particular engine and where it makes power I would likley start with a AA or maybe an A
    Perfect. It seems like an A cut is the way to go. Now my question is, Iíve got a JC berk. When I go to replace the impeller what else should I do to give it a refresh?

    Ive found this kit: http://www.berkeleyjet.com/p-73944-b...-ring-kit.aspx

    Do I need/want anything else to get this job done?


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    Quote Originally Posted by 71BeaterBoat View Post
    Perfect. It seems like an A cut is the way to go. Now my question is, Iíve got a JC berk. When I go to replace the impeller what else should I do to give it a refresh?

    Ive found this kit: Berkeley Jet Drive - Berkeley Impeller / Shouldered Wear Ring Kit

    Do I need/want anything else to get this job done?


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    That motor is basically a "grunt motor" and probably makes most of its power around 4200 , AA would work well with that IMO

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    Call Tom at Jet Boat Performance, 805-466-4719. He's the expert and he can save you some money. They machine their own impellers and he can tell you exactly what else you need.

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    Senior Member bp298's Avatar
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    an A or A/B will work fine in that boat, as long as the pump's tight. you deal sounds like clearances are severely worn to get that poor performance from the hit. getting the clearances right (wear ring/impeller shoulder/impeller depth) can make all the difference.
    keep in mind that starting the engine in very shallow water, like less than 4-5', can draw sand/dirt/gravel off the bottom and through your pump. that stuff affects clearances. running the engine on the trailer with the pump spinning can affect clearances. doesn't kill the boat, but affects performance in the areas your boat has lost it.
    good luck with it.

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