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Thread: 4-TEC props

  1. #1
    Phil's Avatar
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    4-TEC props

    Hey guys,

    I trust that this forum includes 4-TECS as well as RXPs. Well, here goes.

    Please post your results with trying different props. It seems that nobody yet has dialed in the right prop combination for 250+HP (on the dyno, not the B.S. meter) 4-TECS. My current prop is a Mark Underwood modified OEM prop that turns 8,400RPMs and gets me great acceleration (although it cavitates like crazy out of the hole), ballistic mid-range but hits the rev limiter on the top end - resulting in a top end of between 69-72MPH (GPS) depending on the fuel load, temp and barometer.

    I am working with Dave (Impros) on a Solas 15/22 4-blade. The first run; it dropped my RPMS from 8,400 down to 7,700 and my speed went down to 67MPH (GPS). He is now cutting it down to a 15/20+. I will try it again this weekend and post my results.

    I am trying to avoid installing the split drive shat and the full blown Magnum pump and 3-blade prop until someone has tested the combination and found the right combination. It is comon knowledge that the Skat Magnun Pump is the best pump around, but I don't think anybody has found the right prop combo yet.

    This could be a great thread for a combined effort of 4-TEC enthusiasts if we help each other.


  2. #2
    Site Admin Green Hulk's Avatar
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    Great thread Phil!

    I think you will find great results with that Solas 20 pitch. Maybe even a 20.5 would be better?

    Let us know how it turns out.

  3. #3
    mgo7483's Avatar
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    Re: 4-TEC props

    Quote Originally Posted by Phil
    I trust that this forum includes 4-TECS as well as RXPs. Well, here goes.
    Seeing that the RXP has 4-Tec, I would guess your right...

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    Phil's Avatar
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    Today's results on my Race Tech 4-TEC SC

    Date: May 14, 2005
    Time: 3:00 PM
    RAD = 97%
    Hygrometer = 68
    Elevation - 800 ft.

    Test were done using 2 GPSs. There were 2 riders of different weights testing the Mark Underwood repitched OEM prop.

    First Brent (150 lb.) made a run in the slop (1 to 1.5 foot) of 68.9 using a full to the brim tank of fuel. Acceleration was terrific. Mid-range punch was incredible. Brent made another few runs in a back cove in very smooth water and go a best of 71.6MPH on the GPS at 5 bars of fuel. All runs buried the tach at 8,400RPMS.

    Next Eric (220 lb.) did the same test starting with 5 bars of fuel. Eric got a best of 68.4 in the slop and 70.6 with 4 bars of fuel. Eric was very impressed with the punch. All runs buried the tach at 8,400RPMS.

    At about 5:30 PM we finally switched props to an Impros 13/12 X 21. This prop was originally a 15 X 22 which Dave repitched for the second time.

    Brent's best run was 68.7 (7,720 RPMS) on Radar (68.6 GPS). The hole shot was better than before, but the mid-range sucked. We lost 3MPH on the top end. What a disappointment!

  5. #5
    Site Admin Green Hulk's Avatar
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    Phil, thanks for the report! Sounds like that 21 pitch is still too much as it's killing your RPM's.

    I just ordered a new Solas repitched by Dave to a 15/20. I will be running the Rotax Racing full blown Stage 3 on this impeller. As soon as i get it all back together i'll be sure and share my results.

  6. #6
    Phil's Avatar
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    Quote Originally Posted by Green Hulk
    Phil, thanks .... I just ordered a new Solas repitched by Dave to a 15/20.
    Who told you to try a 15/20? Dave told me he was going to repitch my 15X22 to a 15X20, but then sent me a 13.5X21 instead. Why? This was a waist of time and money.

    I look forward to hearing your results. Good luck!

  7. #7
    Site Admin Green Hulk's Avatar
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    I told him i wanted it to be a 15/20 as that is what Riva is going to be using on their new Stage 2 kit. I really think i will need more pitch that that though. Maybe a 20.5 or 21. Hell, i may even wanna try yours. We will see!

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    Phil's Avatar
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    I wish 11, Dave Stewart, Mark U., Glenn Perry, Bill O'neal etc. would jump in on this thread. This is the thread that all that horsepower will eventually lead to. For example, if I bought the EMS right now, I may gain 30HP and still have no place to go with props. I am hitting 8,400RPMS now. It is not written that a bigger pitched prop will give you more speed. It just doesn't work that way. It requires tuning and tuning and tuning.

    We need the brain trust of everybody that can contribute to this thread with factual data in order for all RXP, RXT and 4-TECS to benefit. If any BS's this thread they will hurt everybody. Please encourage riders, tuners and mechanics to contribute useful data and knowledge to this thread.

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    Moderator two2curupt's Avatar
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    Hey Phil...I have no clue what we can do with props on our GTX...I think we might be in custom prop land here..I know with the stage 2 kit I am more than fine running the race tech re-pitched stock impeller..I also know that there is a substantial difference between your boat and my boat when it comes to top speed...I too will be getting into the stage 3 rotax kit..(soon) and I know that alot of other ppl will be soon as well so you are kind of the pioneer as far as finding a good (Recreation) prop for us...The race guys don't seem to have the same needs as us so they are more than happy I think with crazy mid range..And sick acceleration..As opposed to you and me and most rec riders that want the top speed instead...Have you asked Mark what they run over in Europe for impellers on thier endurance machines???..I think they run the magnum pumps out there...Unfortunatly I think that will be our route as well... But as I have said as far as trying to run a certain pitch prop on the stock pump...I think you are the pioneer on this.. So what ever your findings are in the coming weeks, will set the guidelines for those of us that don't want to step into the Magnum pumps just yet...

  10. #10
    Vern's Avatar
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    What impeller cones are all of you using? I know in the past there has been some trouble keeping the cones on once impellers are switched ...

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