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  1. #1

    13/18 Solas/SS Wear Ring = 700 rpm drop from stock 10/21 :(

    Stock Challenger 180 215hp. Now 2 hours on boat.

    Chewed Stock impeller and wear ring being stupid. Lesson learned.

    I did the swap earlier this week to 13/18 from Solas and SS wear ring.

    I do feel hole shot is better, but I can't really say how much.

    However, with stock 10/21 impeller, I was hitting 8250 rpms. I was not even giving it full throttle. Now I am getting 7550 at full throttle.

    Top speed today was 44 mph on pretty calm water at full throttle ( I believe in full throttle once in a while during break in period. I am not hitting it for more than maybe 10 seconds at a time...and only two or three times each time out.) I think the top speed with the 10/21 stock impeller was 47 or 48. I have no GPS yet, so this is strickly from the dream-o-meter.

    QUESTION: Did I screw something up during the install? I don't believe I am cavatating at all. Is it possible that I am getting a 700 rpm loss just from the new impeller and SS wear ring?

    Please help.

    Jim


  2. #2

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    When I went from stock to the 13/18 (& SS wear ring), my RPMs went up +100 to 8150, holeshot and accel went up dramatically, and top speed either stayed the same or went down not more than a half of a mile an hour. A couple of engine-hours later, when I added +1 to the trailing edge of the fins, I remember one was off by -2 from the others. Maybe you have a fin or two on the new prop that are way off. I can't imagine how you could mess up the pump re-installation enough to account for that RPM loss.

    To me, you turning 7550 now isn't nearly as strange as you turning 8250 with the stock prop during the first two hours of break-in. A more normal RPM to be turning at WOT, in the first hour of a stock boat, in the middle of the summer, would have been more like 7700-7800.

    You've got to take that new prop out and check it; if I were you, I'd throw the stocker back on there in the meantime and see how it behaves. You've got to make sure that SC (washers) isn't starting to act up on you. Soon you'll be able to take that pump on and off like a NASCAR pit crew.

    If you're going to mod, you can't really be sure of the benefits until you at least get a cheap GPS, though.

  3. #3
    Quote Originally Posted by VX1 View Post
    When I went from stock to the 13/18 (& SS wear ring), my RPMs went up +100 to 8150, holeshot and accel went up dramatically, and top speed either stayed the same or went down not more than a half of a mile an hour. A couple of engine-hours later, when I added +1 to the trailing edge of the fins, I remember one was off by -2 from the others. Maybe you have a fin or two on the new prop that are way off. I can't imagine how you could mess up the pump re-installation enough to account for that RPM loss.

    To me, you turning 7550 now isn't nearly as strange as you turning 8250 with the stock prop during the first two hours of break-in. A more normal RPM to be turning at WOT, in the first hour of a stock boat, in the middle of the summer, would have been more like 7700-7800.

    You've got to take that new prop out and check it; if I were you, I'd throw the stocker back on there in the meantime and see how it behaves. You've got to make sure that SC (washers) isn't starting to act up on you. Soon you'll be able to take that pump on and off like a NASCAR pit crew.

    If you're going to mod, you can't really be sure of the benefits until you at least get a cheap GPS, though.
    Thanks for the reply. I appreciate your insight.

    The stock prop is chewed on the leading edge or I would definately throw it back in right away to see if that makes a difference. I was definately surprised by the stock RPMs as well. Again, I am not staring at the gauges all the time, but the highest I saw was 8250.

    GPS is my next purchase.

    Two questions.

    Would the supercharger washers slipping account for RPM loss?

    and...

    Where is a good place to send a stock or aftermarket prop to be pitch blocked and have leading edge nicks worked out?

  4. #4
    Fast & Loud meeper's Avatar
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    when going with a larger prop you need to put on some power adders to get your rpms back up, i would do intake and see what happens

  5. #5
    Quote Originally Posted by meeper View Post
    when going with a larger prop you need to put on some power adders to get your rpms back up, i would do intake and see what happens
    So 500-700 rpms is likely lost just from the impeller swap? Interesting. I wouldn't have thought that. Live and Learn. Won't an intake void my warranty?

  6. #6
    GTI06's Avatar
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    I put on a solas 11/19 which is steeper than the stock and I went from 7300 rpm to 6500. It takes more power to push a steeper prop.

    also when you saw the 8200 were you airborne for a second? If prop is out of the water it can spin up briefly.

  7. #7
    Quote Originally Posted by GTI06 View Post
    I put on a solas 11/19 which is steeper than the stock and I went from 7300 rpm to 6500. It takes more power to push a steeper prop.

    also when you saw the 8200 were you airborne for a second? If prop is out of the water it can spin up briefly.
    Could be that the 8200 was while sliding and spinning...love these boats. I do know that I am not full of crap and that I saw 8250. Unfortunately, I was only an hour into the break in before I chewed the stock wear ring and impeller and I didn't make much note of wide open throttle passes regarding RPMs. I know that I hit 47/48 mph though.

    I guess I am not really concerned about the loss of RPM considering that I don't plan on modding too much. The holeshot is definately better with the new prop over stock. Top end seemed to drop by 3-4 mph. Not a huge deal for me, since where I boat I am not able to hit top speed for that long anyway.

    I like the idea of an intake to raise the rpms back up a little, but I am not sure how to set it up. Don't seem to be a lot of C180 folks on this forum.

  8. #8

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    when going with a larger prop you need to put on some power adders to get your rpms back up
    Is a 13/18 really considered larger than the stock 10/21? I'm a frickin' engineer, so quite frustrated that I still don't feel I have a complete grasp of prop pitch. Acceleration is better than stock and topend is not as good with the 13/18, so it would seem to me that it would be analogist to a smaller gear, a smaller prop? I've got the concept of the final number, but as far as the first, which is taking a larger bite out of the water with each revolution, the 10 or the 13?

    Won't an intake void my warranty?
    Legally no, but they can TRY to do whatever they feel like. Nevertheless, it's usually a quick process put the stock intake back in place. With that said, if someone customized their intake in a bad way that caused a failure (water ingestion), then they have every right to void the warranty.

    I am not staring at the gauges all the time, but the highest I saw was 8250.
    You would really have needed to know your AVERAGE RPMs at full throttle heading in a straight line to be able to do any reliable comparison.

    Would the supercharger washers slipping account for RPM loss?
    Most definitely, but on a SC with such low hours, I would think unlikely. There have been so many low-mileage '07 superchargers blow their washers, but at 7550rpms, that of course is not the case for you. So the factory could have somehow not made the slip moment tight enough, but since this just started when you took off the pump, having the SC slipping now would be coincidental. "Might" be time to get the steel washers; at least when you get it back, you'll know the SC will be tight.

  9. #9
    Website may not be suitable for small children WOT's Avatar
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    Maybe you could check to see if your intercooler is clogged. That could account for a loss in rpm. Depending on what you hit to damage your prop, maybe a bunch of crap got packed up into the intercooler -- just a guess...

  10. #10

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    Send your damaged impeller to impros for repairs should be between 50-75 dollars. Then reinstall the stocker and start from there. BTW if you still have your stock ceramic SC washers in there your about to learn hard lesson #2 when you blow the SC clutch. Get the metal washers!!!!
    www.impros.com
    TCR

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