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  1. #1

    Join Date
    Jul 2005
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    RXT 74.2 MPH on the limiter

    Just got off the lake and very pleased. Itís going to hit 75ís soon. Iím starting to like this RXT over my RXP a lot. This big tank is starting to feel fast and amassed how it handles the chop were I would have to abort my RXP speed runs. It doesnít like the Riva Grate at all and felt like it was pulling down and trying to unhook, so I arrow dynamic shaped the stock grate runners and ported the pump housing which works really well. Left the 2 degree wedge in and adjusted the steering nozzle down .045Ē. Installed my Rotax cam in a full retard position and with no headwork is killing the limiter on a .020Ē de pitched 14/19 Solas. Tomorrow Iím going to put in a stock 14/19 Solas and made most of my runs today backing off a bit as not to float the vales on the limiter at 8500. GPS 74.2 MPH. Several times, Full tank fuel, 80 deg air temps, 9.2lbs boost, 76 deg water temps.


  2. #2
    You da man! Don't forget to update that sig.

    What is porting the pump housing ? Did you dremel it out ?
    So did you notice any differences with the nozzle down a bit ?

    Here comes a 80+ RXT....

  3. #3
    R.I.P. 11's Avatar
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    Time to change your signature...

    Impressive.

  4. #4
    Moderator two2curupt's Avatar
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    I was only able to see the 73.8 mark on mine...Turns out my sc was only pushing 4.5-5 lbs boost at that point...I was running the stock cam as well..Now my biggest enemy is my pump..I seem to be getting into a flex issue again...I think once the water temps drop up here 75mph will be a non issue...Did your boat feel like it was lurching forward at top speed...like it was stuffing air almost?

  5. #5

    Join Date
    Jul 2005
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    Yes I noticed changes in the way it felt on the water and the way it stayed hooked up. On my RXP moving the nozzle up or down seemed to do little with ride, on this boat it makes a big difference. Tried it at .120Ē and felt the nose down and bow spraying just a bit .5 MPH loss, at .045Ē it felt light but very controlled. With Riva grate and 2 degree wedge when punching it out of the hole would bow up to much and UN hooks. The Riva gate only really works when the wing is close to correct angle with the water. Up or Down from that mine felt like it was either pulling down or UN hooking was the same with my RXP (Which by the way I have both and willing to part with cheap). I think the stock gate when shaped correctly puts more water in. Porting the pump hosing removes all the casting flashes that allow more water to pass with less effort.

  6. #6
    Thanks for the info. I tried porting my pump housing but wasn't sure if I was doing it correctly. First I used a dremel and a sanding drum to get the back side. Then used 600 grit sandpaper with my hands to try to sand it. Didn't seem to effective. Their is also the bumps on the angled veins and wasn't sure if I should sand those down too.

  7. #7

    Join Date
    Jul 2005
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    Wisconsin
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    I did mine just like a set of heads. Thin out the vaines and not a bump to be found, and everything polished out like chrome

  8. #8

    Join Date
    Jul 2005
    Location
    Wisconsin
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    two2curupt: Does yours have a Riva grate? make it be gone, thats how mine felt with that and the 2 deg wedge. Mark lowered the ride plate on yours I think better deal but I'm to lazy to take it off.

  9. #9
    Is there a special tool for doing this type of work ? or does a dremel and elbow grease do the job.

  10. #10

    Join Date
    Jul 2005
    Location
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    I wouldnít get to carried away on porting the housing unless you know how to shape flow patterns, weíve been doing cylinder head development for 25 years. I even mounted a pump housing on my flow bench looking for flow and velocity patterns through the pump and nozzle. Iíll get more into the pump after I see what fixes the bearing and shaft flex and think itís a point of diminishing return until that. My SS wear ring looks like burned crap so Iím running a plastic one and changing that bitch every 4 hours. There is a lot left in this engine in the head department, valves are crude, springs are minimal, valve seats and angles are 10 year old technology. This winter Iíll get the head on a spintron and really see whatís happening in the valve train. Iím a little gun shy to get more RPM HP after dropping the valve in my RXT. However I am impressed the Rotax Racing cam got me 150 RPM with no porting.

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