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Thread: expansion chamber seals and tuning

  1. #11
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    Quote Originally Posted by Tim Weber View Post
    A good mod will clobber a c-stock.

    My 500MR is about 5 mph better than my c-stock and my stocker is no slouch. I'm finding about 500 more rpm with lot's of punch with the mod.

    As far as props the three will run just as fast as the four blade but what I've found is the four holds your speed better in the turns so the eta with the 4 blade for me is better.

    Tim
    Tim, I always wondered about how fast (mph) the MR boats are running around the turns. I figure that on a mile coarse, the turn radius is maybe 400 or so ft? I asked about this before, but never got any answer directly about it. I know your C-mod boats are flat turners. Im thinking of making my "B" hull as such. A four blade as you describe sounds like a positive choice as well! You got me re-thinking about it! Also, roughly what range of rpm do you run in a complete lap in Mod Runabout? Thanks.

  2. #12
    Tim Weber
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    I really don't know what the average rpm is. I don't have a Mychron unit.

    Just looking at a Tiny Tach testing I'll lose 500-800 rpm in the turn BUT that depends on the prop and how big of a turn. If I'm on a big 5-6 pin turn it's not all that much.

    Tim

  3. #13
    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by Tim Weber View Post
    A good mod will clobber a c-stock.

    My 500MR is about 5 mph better than my c-stock and my stocker is no slouch. I'm finding about 500 more rpm with lot's of punch with the mod.

    As far as props the three will run just as fast as the four blade but what I've found is the four holds your speed better in the turns so the eta with the 4 blade for me is better.

    Tim
    "A good mod will clobber a c-stock" Yup.. Racing in Berwick Pa, won CSH Sat., had the fever & was doing better than usual. Sun was combined w/ 500MH, I wanted it bad, nailed the start & gave it all there was but there just was no catching Dave's 500. You don't have to be the fastest in your class to have a good day now & again but overwhelming speed sure has its way.

  4. #14
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    There is no comparison between a stock and a tuned exhaust motor. The tuned expansion chamber gives the engine so much more from midrange and up.
    I have been running a C I built for a few years and recently built a y80 mod. I was very impressed with the power I got with the 80. I've only run it a couple times, but I am seeing speeds in the low 70s on a hydro. I'm running a two into one header and a pipe I made for my C.
    Good luck with your build. I'm curious on how your two chamber system will work. As for the pipe sealing, taper your header pipe out and it will slide well.

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