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  1. #1
    JFizzleJR's Avatar
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    My Test Results (need some help)

    Well, everyone seems to start a thread dedicated to describing a day of testing their ski. I decided to follow suit now that everything is finally together.

    Okay, the mods done to my ski (2005 Viper Red RXP) are as follows:
    Riva Intake Grate, Riva Thru-hull exhaust, 2° Wedge, SS Wear Ring, 15/20r w/ 2 mm added, Rotax High Boost wheel, Jerry's '06 metal washers, Pirahna Solid Front Motor Mount, Rotax 42# Injectors, XS I/C kit, Riva Rear Intake, No Flo-Rites, Dynotune Boost Gauge, Rideplate Holes Filled, Reverse Bucket Chopped..I think that's it..

    Rider Weight: 165 lbs., Gas Level: always between 3-5 bars.

    First time out with a 15/19R 3 blade I pulled off 72.9 in the chop with OPAS intact and porpoising @ 8100 RPMS and 81mm ring. 300 ft. elevation, no boost gauge. 4" front air intake.

    2 weeks ago at 1300 ft. elevation hooked up the boost gauge. RPMS went from 8100 to 7900 after increasing elevation 1000ft and boost went from 7.9 to 6.5 in 10 minutes of riding. 4" front air intake this time too. Eventually RPMs dropped to 7600 so I put in the 15/20R (too steep b/c of the 2mm added) and stayed the same RPMs but increased 3 mph. 67.8 @ 5.9 lbs of boost.

    This time, same lake as the first test, 15/20R 4 blade, RE Block-offs, 83mm ring and rear intake. 5 bars of fuel: 73.7/8/9, 74.1, 74.3 mph @ 9.1 lbs of boost @ 8100 rpms. At first I had a check engine light and 2 error codes, but I quickly remember the o2 sensor wasn't plugged in. After that everything was normal except for Idle.

    So, the temps are pretty cool here in NY (water low 70s, air upper 60s) so I was expecting 76+..72.9 w/ porpoising and 15/19R 3 blade. 74.3 without porpoising, 15/20R 4 blade and rear intake..The only thing I changed was the prop, intake, and ring size.

    My questions are:

    1) Since last time out my idle went from 1750/1850 to 2350/2450. How do I get it back down to normal and does it indicate something that is causing me to lose top speed?

    2) The prop has 2mm added to it (was spinning 8400 w/ a b-kit). Even though I got it dialed in to hit 8100 rpms, could I still be 'over-propped'??

    3) Since I had to swap the 81mm ring for 83mm to get the RPMS up should I put the 81mm back in, check RPMs, and pitch accordingly? In other words, if I change rings to 81 and it drops RPMs, then I re-pitch to get back to 8100 should I expect to increase speed from the last test with the 83mm?

    Alright, I believe I can honestly say this is my longest post ever. Thanks to whoever takes the time to read it all and trys to point me in the right direction. Like I said earlier, I've got high 73s and low 74s for speed and am expecting to run 76-77 especially after I add skegs soon. Only 2 problems are idles 600 rpms high and speed is about 2 mph low. Any help would be greatly appreciated.

    Thanks,

    James


  2. #2
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    try a different ring....

  3. #3
    JFizzleJR's Avatar
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    How much speed do you think I will gain with the 81mm ring at 8100? I'm at 74 mph @ 8100 with the 83mm ring now. Obviously I'll have to re-pitch after changing rings..Is a 2 mph gain too much to expect?

    My biggest concern is finding out why I'm idling at 2350-2450 instead of 1750-1850.

    Edit: Humidity was about 90%. About how much speed loss could that account for compared to an average day?
    Last edited by JFizzleJR; 07-04-2007 at 10:23 PM.

  4. #4
    Quote Originally Posted by JFizzleJR View Post
    2) The prop has 2mm added to it (was spinning 8400 w/ a b-kit). Even though I got it dialed in to hit 8100 rpms, could I still be 'over-propped'??
    How come did you switch from the B-kit?

  5. #5
    JFizzleJR's Avatar
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    I didn't ever have a b-kit. I purchased the prop from someone who had a b-kit then sold it to another person that had a b-kit because I purchased the 15/19R. When I found out the 3 blade wasn't the greatest for top speed (especially with 250hp at 8100 RPM), I bought the prop back from who I sold it to.

  6. #6
    Quote Originally Posted by JFizzleJR View Post
    I didn't ever have a b-kit. I purchased the prop from someone who had a b-kit then sold it to another person that had a b-kit because I purchased the 15/19R. When I found out the 3 blade wasn't the greatest for top speed (especially with 250hp at 8100 RPM), I bought the prop back from who I sold it to.
    Ok, I see!

  7. #7
    JFizzleJR's Avatar
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    Went out today and was down to 7950 RPMs, saw 8000 once. What I don't understand is my boost went from 9.1 down to 7.5 with the rotax high boost wheel. Does each 10 rpm = .1 lbs of boost or what?! Squeezed off some high 72s. Couldn't hit 73 mph. This is pathetic.

  8. #8

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    YOU'VE GOTTA spin that motor to 8100 to get 10lbs...To much prop.

  9. #9
    JFizzleJR, have you run a compression or leakdown test just to verify that the engine itself is ok?

  10. #10
    JFizzleJR's Avatar
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    Quote Originally Posted by jawz View Post
    YOU'VE GOTTA spin that motor to 8100 to get 10lbs...To much prop.
    I was turning 8100 last week to get 9.1 lbs. Same prop, same pitch, 10 degrees warmer and down 1.5 lbs of boost.

    Quote Originally Posted by RXPkid View Post
    JFizzleJR, have you run a compression or leakdown test just to verify that the engine itself is ok?
    No

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