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Thread: Wild Theory

  1. #1
    Moderator Franko's Avatar
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    Wild Theory

    I'm looking for some input on a theory I have come up with. Jarrett and I have now built three skis with basically the same mod platform. RR ECU, RR or Riva IC, RR SC impeller & 42 lbs injectors, 15/20 prop (out of the box or GH tweaked), 4" air intake, exhaust mods (thru hull or power pipe), all free speed mods (ride plate holes, nose cone etc), OPAS B/O, Riva grate. Most other people in other areas of the country get 76-78 mph out of this type of set up. We consistently get 74-75 and the RPM always seem to stick at 8250-8300 maximum.

    With seemingly a "cap" on our RPM, I'm thinking there is a sensor issue somewhere. But like I said, this has happened with 3 different skis now. The only common denominator is that all 3 skis ride in the same places at the same times. So I'm wondering if our water/air conditions contribute to the problem. Perhaps our conditions cause our exhaust to run hotter and the exhaust temp sensor signals the ECU to add more fuel to the mix resulting in a rich condition? I added the b kit and fuel controller to my ski, and the "capped" RPM issue went away. That makes me think it is related to the fuel flow from the ECU, because with a piggy back fuel controller, the problem stopped.

    I plan on testing my theory by securing the exhaust temp sensor to the hose off the coolant tank. Are there any other sensors that provide input to the ECU with respect to fuel flow?


  2. #2
    Jarrett's Avatar
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    I can back this up. 8250 seems to be my magic RPM cap number. Sometimes I can get beyond it, but that is the exception rather than the rule. And I've seen this in air temps from 70 to 100 degrees with no RPM change.

    Yesterday, I made one run and hit 8380 RPM in 95 degree air / 87 degree water at 530ft altitude. I turned around and hit 8240 going the other direction and continued to only hit 8240-8260 after that. Later on while goofing around with holeshots, I accidently hit the start/stop button. I restarted the ski and hit the throttle again and it immediately ran back up to 8360 RPM and stayed at that limit for the rest of the ride.

    I had this exact same thing happen at MB2 in June. When Frank did the radar run on my ski, it was only hitting 8250. Then later after stopping for gas, I could hit 8350-8400 RPM in hotter air. But then later after letting the ski sit for about 30 minutes, I could only run 8250 RPM again.

    These events lead me to believe that there is something that is slowing me down electronically. Like Frank said, I am assuming its the waterbox sensor, and I need to move it to verify. One time I ran without the waterbox sensor plugged in and all I could hit was 8250 then as well. Has anyone else had this happen or found a fix for it? Thanks.

  3. #3
    EZ Dock of Long Island Shibby1485's Avatar
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    have you guys played with the little yellow restrictor washer on the water inlet by the pump?

    i know someone that was stuck at a similar point, big boost setup so the sensor was always picking up high EGTs i guess.... they drilled out the yellow washer two sizes larger and saw a 200+ rpm increase just from that alone

    i wans't there, i never tried it, but he swears by it... might be worth a try?

  4. #4
    EZ Dock of Long Island Shibby1485's Avatar
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    this i why PRs setup is actually a great idea that was sort of blown off.. ESPECIALLY in u hot air/water climate guys.

    you increase boost, compressed air is running hotter, water passing thru intercooler is getting even hotter from the boosted air, and now your cooling down an extremely hot exhaust with hot water... and by the time it goes thru the exhaust manifold and j-pipe that water has got to be boiling in the waterbox making that exhaust sensor live on the edge..

    run separate water for the exhaust and separate water for the intercooler... fresh raw water goes to each

  5. #5
    Moderator Snoman's Avatar
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    Hey Shibby would this also work for the RXP??? What if you took that washer out all together what would that do ???or do you need some resistance going into the exhaust??

    Thanks
    Scott

  6. #6
    EZ Dock of Long Island Shibby1485's Avatar
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    u need some sort of restiction bc it maintains more constant pressure, less explosive surging to the intercooler core when the ski gets unhooked.

    removing it all together would probably reduce the velocity of the water flow?

    alot of science goes into intercooler efficiency which i'm no pro at.. there's a point where too much water flow doesn't allow good heat transfer of the compressed air. too little flow doesn't cool well either...

    it'll definitely work for an RXP... i'm in process of doing something similar on my "new to me" RXP

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    Moderator Snoman's Avatar
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    Awsume..Gonna give it a try..Thanks Shibby

    Scott

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    HOSS's Avatar
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    Thumbs up

    In regards to heat transfer on the system in questionall AUTOMOTIVE technology/experience you can literally throw out the window. The system is in constant water and constant fresh water. The heat transfer is constant. In fact the water flowing at a high rate will cool the metal.
    This system is nothing like an air system. That does need heat transfer. This is different. WAY different. Yank the themo.

  9. #9
    HOSS's Avatar
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    Quote Originally Posted by Snoman
    Awsume..Gonna give it a try..Thanks Shibby

    Scott
    I`m thinking along the same lines here.

  10. #10
    Moderator Snoman's Avatar
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    Hoss, My riding seasons almost done up here.Im gonna try to get this done asap ..If you do this anytime soon could you post results??Ill Do the same

    Scott

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