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  1. #1
    somefun's Avatar
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    Can't finger it? 500HP Impeller test

    Guy's I have been going crazy with this. Let me know what you think. Installed RR 4501 ECU, custom full 3" intake with 9"x6" K&N filters, XS Power Intercoolers, SS wear rings, filled ride plate holes and cleaned up the intake grate and rear jet nose cone . The boat ran stock 58.5 at 7100 RPMs. Then it went to 7700 to 7800 and ran 66.8 and both runs were with stock 10/21's. Then I went to Skat 3 blades that were 13/17 and it ran 8300 to 8400 and went 67.0. But it slipped a lot on acceleration. So I sent Glen my stockers and had him clean them up and make them 10/19's. He balanced them and slight polish job. I took them out tonight and the boat ran 66.0 at 8400 RPMs. Hitting the limeter so it may have been 8500 rpms. The acceleration was nuts! But why is it turning so many RPMs? The only thing I can think was maybe the impeller was not the 10/21 I thought it was or Glen balanced it better or thinned it by polishing it. So now I have to figure out how much to re pitch it. I want to turn it to 8000 or 8100. So I was thinking of going to 10/22. Does this make sense????


  2. #2

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    Somefun man I am telling ya...go to 4" intakes and you will get anoutehr 100-150 rpms out fo thsoe engines!

  3. #3
    Yuji's Avatar
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    Did Glen verify the stock pitch before he did the re-pitch?


    You're seeing almost the same mph and much better acceleration with a 10/19 repitch (6-700 more rpms) vs stock with intake mods correct? I think the re-pitch helped and is loading the pump all the way thru but then yer bangin' the rev limiter which is hindering mph. This would require an increase in pitch, say 10/21 wait...thats what the stock impellers are !

    Geeze somefun I wish I could help Until I get out and try mine I'm at a loss as to what to do next. Maybe the stock pitch was something like 13/23? Thats what comes on the naturally aspirated sportster
    I changed mine from a supposed 10/21 to 12/19. 12 should load the pump more and improve accelleration and 19 to bring my revs up from a best of 7750 to hopefully 8100.

    Don't forget air temp, lake temp, boost leaks, rev limiter etc. can skew yer results. You sound like you are fairly mechanically inclined...why don't you try bending the trailing edge yourself, 1mm at a time. As long as you are still makin the revs you should be able to ad pitch.

  4. #4
    somefun's Avatar
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    I was going to bend it myself but Glen did something because all my test results have been under the same conditions as far as tide, wind, fuel and so on. The stock pitch was 10/21 or so the boat dealer told me. I'm thinking that it wasn't or if it was they were all off a bit. Also I'm wondering maybe Glen straightened it out and then the polish and balance had to have something to do with it. I think I'm going to send them back and have him make them 10/22's. I want Glen to do it because I want everything to remain a constant in the way I'm doing the tests. The way this thing ripped it has to have 2 more MPH left in it for sure. I think it's going to be right at 68. The only problem is if it goes to 69 mph then I have to get the RR impellers to get the magic number.....

  5. #5
    somefun's Avatar
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    TB what kind of piping should I get to make 4". I used PVC for the 3". It's actually 3.5" oust side diameter. I think it wouldn't do that much because you have to neck it down at the supercharger?

  6. #6
    Yuji's Avatar
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    Yeah...knowing they are balanced and pitched to your specs properly is worth something. If you put the RR impeller and injectors on there...that things going to be a monster!

  7. #7
    somefun's Avatar
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    yeah. I'm trying to hold off till winter. That way it will give me something to look forward to. I pissed though because I can't get the 4 blades back in time for the weekend. So I guess I'll take them off Sunday night and ship them to Glen for Tuesday.

  8. #8
    Yuji's Avatar
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    I just recieved my 3 blade 13/17 and SS ring 10 mins ago...would you suggest I just send both back? Not sure now if that 3 blade impeller will be what I want now...Also, hows the SS ring been working for you?

  9. #9
    Yuji's Avatar
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    Okay...so I threw the Watcon pitch gauge on my new 3 blade 13/17...guess what it comes out as

    10/15 !

    Now...that doesn't mean it's wrong but it just goes to show you that everyone measures their impellers differently. It would sure be nice to see if Glen checked the pitch of your stock ones before bending...I'm sure he did. Wish I could check your stock impellers with my pitch gauge, then I could compare apples to apples...sure liking this impeller pitching stuff

  10. #10
    Top banana's Avatar
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    somefun remove the props and get the part no then look the pitch up and go from there

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