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  1. #1

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    Considering a 15/22 Dynafly. Will it work?

    I recently finished my 2000 GP1200R conversion to a 1300. I'm still fine tuning the carbs, but for now I'm fairly close. I can run 67mph (GPS) at 7150rpm for extended periods (15+ minutes) with brisk acceleration from idle. I'm turning a 14/20 Dynafly impeller and I think I am firmly up against the rev limiter with this combo. I'm wondering if I can pull a 15/22 Dynafly without losing too much acceleration. Does anyone have any experience with a similar combo running a similar impeller?

    The engine has stock: porting, single pipe exhaust, power valves and CDI. The hull is stock and has a stock ride plate and trim tabs.

    List of Modifications
    Rejetted carbs, drilled return restrictors and removed accelerator pump - Fuel pressure is 2psi at idle and 7psi at 7000rpm
    Filled intake manifold channels for better carb signal
    V-Force 3 reeds
    Removed stock airbox and added Pro K flame arrestors
    Millenium overbore, replate and finish hone
    Head machined for larger bore (cold compression 127-129 with 3-Layer gasket)
    Several cooling mods to improve cooling for #3 cylinder and decrease exhaust water flow
    D-Plate and resistor
    Riva Free Flow exhaust
    HO pump blueprinted with stock cone
    Rooster tail port plugged and suction pipe trimmed shorter
    Worx 1200 intake grate, PPK and pump sealed with 4200
    Increased side cover airflow
    4 Degree advance key
    14/20 Dynafly impeller

    Thanks in advance for your input,
    Mike



  2. #2
    Adam's Avatar
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    You could use the 85mm exit nozzle instead of the 87mm for more speed before changing the impeller.

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  4. #3

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    Thanks, Adam. I bought one off eBay tonight and should have it on the ski by next week. We'll see what she will do!

    Mike

  5. #4
    jgustman's Avatar
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    You’re not up against the rev limiter at 7150 rpms. It’s rev limiter is around 7400-7450 rpms. You will not be able to pull a taller impeller without lugging the motor. Most made the best speed and power at 7250 or so, but that was with higher compression and v-force reed package back in the day.

  6. #5

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    Thanks J, for some reason I thought I read that max RPM was 7200. Oh well, good to know that I have some room before I reach the RPM limit.

    I installed the 85mm exit nozzle today and was able to reach 68mph (GPS) and noticed my RPM was down 10-20rpm for a peak around 7130-7140 (water temp 88, air temp 98 ).

    I have the larger exhaust ring joint pipe ('05-'08 ) that I will install next and see if I get any more rpm out of this engine.

    Thanks again,
    Mike

  7. #6
    jgustman's Avatar
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    That’s pretty good speed for a stock setup. They don’t recommend running much less than 7100 before detonation can become an issue, plus you lose acceleration. Your rpms would come back up some and speed a bunch with an angled R@D ride plate. Have you read this. http://greenhulk.net/forums/showthread.php?t=8691

  8. #7

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    Thanks J. 90% of my riding is in rough water with 1-2ft chop and some days 3ft. I'm leery of giving up rough water hookup for a few mph on the top end. Also I'm not interested in spending too much more money on this ski. I read through that topic last week and concluded I didn't want to spend the money on a ride plate that primarily boosted top end speed.

    Yesterday I got the new ring joint exhaust pipe installed, but I couldn't find any water smooth enough to get a steady rpm reading. Maybe early tomorrow before the wind picks up and all the boaters start tearing up the lake I can get a few speed runs in.

    Mike

  9. #8
    jgustman's Avatar
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    Yep, you’re going to be slower in that kind of water bouncing all over with an angled ride plate. I believe shredmaster plates were popular for that type of riding you’re describing. You may also be losing some rpm’s with the free flow exhaust... stock sound suppression made more hp supposedly. Getting the head cut for around 150 compression to safely run premium pump gas will wake it up for not much money. Lowell Horning was the guy back in the day to do all the motors. I think he referred me to this guy, https://www.wcporting.com/testimonials.html

  10. #9
    Adam's Avatar
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    I see you still have a stock rideplate , an R&D plate is way faster .

  11. #10

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    Originally Posted by jgustman
    Yep, you’re going to be slower in that kind of water bouncing all over with an angled ride plate. I believe shredmaster plates were popular for that type of riding you’re describing. You may also be losing some rpm’s with the free flow exhaust... stock sound suppression made more hp supposedly. Getting the head cut for around 150 compression to safely run premium pump gas will wake it up for not much money. Lowell Horning was the guy back in the day to do all the motors. I think he referred me to this guy, https://www.wcporting.com/testimonials.html
    I buy marina gas almost exclusively, so this ski rarely ever sees anything above 87 octane. My compression yesterday was 129-133, and I'm happy with that. I don't want to compromise long term reliability for a few mph and I hate hauling 5-gallon gas cans to the gas station and down to the dock just so I can put in 93 octane. As to the free flow exhaust, I think I recall reading it may hurt speed a small amount but that the engine ran cooler. If that's true, that's a good trade for me.

    Originally Posted by aDAM
    I see you still have a stock rideplate , an R&D plate is way faster .



    Adam and J you guys convinced me to upgrade the ride plate. I found an R&D Speedplate for <$200 locally and ordered it. The claim is improved handling and less porpoising over the stock plate. These are both qualities I would like to see.

    Regardless, I guess I'll stick with the 14/20 DF. I had some decent water for 1 run today and saw 7200 RPM again. That ring joint exhaust was good for 60-70rpm. Maybe with a ride plate upgrade I can hit 70. This will likely be the last mod for this ski. I'm pretty happy with the performance now and whatever speed I hit with the ride plate will have to be enough...until I buy an 1800.

    Thanks, guys,
    Mike

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