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Thread: Stainless 3 blade Impeller

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    Member Crumm's Avatar
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    Default Stainless 3 blade Impeller

    I have read that upgrading from Aluminum to Stainless impeller on a outboard is not good on motors smaller than 100hp as the gain in hole shot is not worth the loss in top end. When talking about this upgrade people are normally talking about 3 blade aluminum vs 4 blade stainless. Would switching to a 3 blade stainless change the performance at all? I need the stainless for durability as the aluminum impeller in my new jet has already taken a bad beating but I don't want to lose any performance.

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    I believe you are correct. The 4 blade "D" impellers in stainless definately rob some top end RPM, but do give you some more oomph. At least it did on my 115 FICHT. Don't think you would notice any loss of performance with a SS 3 blade.

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    I've never seen a 3-blade SS impeller. I've had a few. Loved them in 200hp. Not good in my 50hp. All 4-blade.

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    Quote Originally Posted by Mr. Pid View Post
    I've never seen a 3-blade SS impeller.
    Well then here you go.


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    Cool. If your were in Anchorage I'd let you borrow my 6 1/8" 4-blade to compare them.

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    I have not picked up a 3 blade yet. Wanted to make sure it wouldn't kill my performance first but I guess no one has tried one.

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    In all seriousness, I don't know whether the 4-blade impellers use a milder pitch or not. In my 200hp motor I had plenty of power to cavitate the impeller at initial throttle-up. The 4-blade helped that considerably. I never noticed any decrease in speed at the top. With my 50hp? I never had enough power to cavitate the impeller and never noticed any out-of-the-hole improvements at all. I did notice a decrease in top end speed, obviously from the motor's inability to spin up to full RPMs. It would be interesting to find out what the pitches are of the 3 and 4 blade impellers. If the SS 3-blade is identical to the aluminum 3-blade the only difference would be total weight, and I doubt that would make a performance impact. But I may be wrong. Please pass on what you learn!

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    I put a 3 blade stainless in a 50hp Yam 2-stroke on a 16' Lund. Saw better hole shot and better performance with a load. Didn't check top speed.
    "The older I get, the better I was."

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    Travelers do you think you have better hole shot with the SS because it is new as where your Aluminum one was probably wore out or do you think it does have a different pitch than the Aluminum?

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    I think it being new has something to do with it. The old one was pretty beat, I did smooth it as much as I could. The extra blade might help the hole shot. Both were shimmed up as close as possible.
    I also have a stainless on a wooly w/90hp Honda, it'll take more of a beating than the aluminum blade.
    Where did you get the 3 blade stainless???
    "The older I get, the better I was."

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    Quote Originally Posted by travelers View Post
    I put a 3 blade stainless in a 50hp Yam 2-stroke on a 16' Lund. Saw better hole shot and better performance with a load. Didn't check top speed.
    Quote Originally Posted by travelers View Post
    The extra blade might help the hole shot. Both were shimmed up as close as possible.
    So you have a 4 blade or a 3 blade? Your first post say's 3 blade SS but then you say extra blade so I am now confused. The stock Aluminum is 3 blade. The aftermarket 4 blade SS will add hole shot but it takes some top end away. I am wondering if there is any performance changes with a 3 blade stainless as I like my performance the way it is I just want more durability as after just two hours of use my aluminum impeller looks a little rough.

    Part number for the 3 blade stainless in a 6-1/8" is 1737 and you can order them anywhere you normally get your impeller.

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    Quote Originally Posted by Crumm View Post
    So you have a 4 blade or a 3 blade? Your first post say's 3 blade SS but then you say extra blade so I am now confused. The stock Aluminum is 3 blade. The aftermarket 4 blade SS will add hole shot but it takes some top end away. I am wondering if there is any performance changes with a 3 blade stainless as I like my performance the way it is I just want more durability as after just two hours of use my aluminum impeller looks a little rough.

    Part number for the 3 blade stainless in a 6-1/8" is 1737 and you can order them anywhere you normally get your impeller.
    Sorry, it's a 4 blade stainless. I don't use my brain as much as I should.

    I think a 3 blade stainless would give you better performance over a 3 blade aluminum because of the thinner blades on the stainless impeller.
    "The older I get, the better I was."

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    This weekend I had a little parking issue on a gravel bar. Sadly I parked it at full throttle! After floating the boat and clearing the rocks from the grate I found my engine apparently has a rev limiter. Maybe my old 2-stoke had one but its really apparent with the 4 stroke. Obviously I had done some damage to the impeller and sleeve, so I dropped the foot to fix it. The sleeve was fine. barely scored. The impeller clearance appeared fine as well, but the leading edges were a mess. I guess the blunt leading edges were causing impeller cavitation and allowing the engine to over-rev. Rather than filing the edges I installed my 4-blade stainless impeller. The over-revving was gone for sure. Other than that, I can't tell any difference in out-of-the-hole performance and it revved from idle to full throttle fine, but I believe the top speed is slightly reduced so it must not be spinning to max allowable RPM. This on a brand new Yamaha 60/40 4-stroke. I'll be putting the 3-blade aluminum impeller back on.

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    Quote Originally Posted by Mr. Pid View Post
    This weekend I had a little parking issue on a gravel bar.
    I find myself with the same parking issues from time to time which is why I want to upgrade to the 3 blade stainless. I am thinking some slick-em on the bottom might help too

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