SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Mar 2002
    From
    Geelong, Australia, Near
    Posts
    272

    Post

    G'day From Downunder Again

    Was just wondering whats the difference between reed valves and the rotary valve. I understand that reeds open from crankcase suction and suck thru fuel and air, and the rotary valve works just like a gate, as it spins around. Is one system better than the other? I thought rotary (800cc) must of been better, but then seadoo went back to reeds for the 951cc. I was told some motor bikes also use a rotary valve. Whats the theory of the difference's between both systems? And which is the better system?

    If reeds are better would it be possible to remove the rotary valve and adapt reeds over the ports? Would it run better, the same or worse? You could always remove the rotary valve shaft.

    I wouldnt do this, but am just curious to understand why they changed, and which is better.

    Thanks Guys
    - From DownUnder

  2. #2
    Joined
    Feb 2001
    From
    Clearwater, FL
    Posts
    7,358

    Post

    No, it's not possible to convert.

    A rotary system is more efficient and can control the intake charge better than reeds.

    Sea-Doo had to go to reeds on the 951 simply because the rotary valve and surface would have needed to be too large to fit on the case for the size of the engine. The 800 is about the physical limit of it's use.

    That being said, I'll take reeds over a rotary and it's associated extra moving parts, extra seals and extra problems - ANYDAY...like Delta 2's or M-16's [img]smile.gif[/img]

  3. #3
    Joined
    Feb 2001
    From
    Glendora, Ca.
    Posts
    5,204

    Post

    BUZZZT ! Wrong answer.

    I have a reed adapter for a rotary valve motor. Tried in back in 1994 on a 657X race boat. Didn't make any improvements, so I ditched it. R&D actually had them in their catalog at one time.
    Bill O'Neal WCM
    <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

  4. #4
    Joined
    Feb 2001
    From
    Clearwater, FL
    Posts
    7,358

    Post

    LOL! [img]graemlins/spit.gif[/img]

    You get some weird stuff Bill [img]smile.gif[/img]

  5. #5
    Joined
    Oct 2001
    From
    Georgian Bay, Ontario, Canada
    Posts
    75

    Post

    Michael, Rotax rotary valve engines were designed for SKI-DOO, not Sea-Doo. In the old days reeds were steel and they were completely sh*t in sub-zero temperatures so companies were stuck with piston port induction on snowmobiles.

    Rotax comes along with the rotary valve for their sleds and it was brilliant. Worked great in sub-zero temps. It was great for the time. All the high output ROTAX sled engines use reeds now.

    In the 90's, if you watched what Rotax put into their sled engines, then you could pretty well guess what might come into their ski lineup a year or so later. Rotax sled engines rev about 1000 rpm faster than their ski engines but are generally much smaller in displacement. Ski-doo produced a 800cc reed induction twin lately, but it blows up more than their other twins.

    I like reeds over the rotary valve in skis for the reasons Bryan has already stated.
    97 GP1200/99 XPL<br />Head, intake and handling mods on both

  6. #6
    Joined
    Jul 2001
    From
    tejas
    Posts
    534

    Post

    the better the performance, the more maintnance. my sea doo racing manual says/show several different ways in which the rotary valve outperforms reeds. but like brian said, it's nice but has more moving parts/things to wear out. in other words, future problems. :(
    cameron "da river rat"<br />3x pro runabout 720 engine blower!<br />(jetskianist~adictionist~modificationist)

  7. #7
    Joined
    Feb 2001
    From
    Tx
    Posts
    38

    Post

    Hey Bill, does that reed adapter fit all the upright motors? If you still have it around, I might be interested. Maybe I could get George to help me redesign the intake tract so it might perform beter....ROTFLMAO [img]/graemlins/cwm27.gif[/img] What type of reed assemblies does it use?

  8. #8
    Joined
    Feb 2001
    From
    Glendora, Ca.
    Posts
    5,204

    Post

    Yes I have it. It uses 650 Kawasaki type reeds and cages. The one I have has aftermarket Boyseens Rad valve reeds in it. It fits 580-720 engines. It even has an R&D intake manifold on it. It may even have a st of blue 42mm taper bored Racing Kehins on it, all set up and ready to go. I'll have to look. I haven't seen it in awhile, but I know where it is.

    How does $200 complete sound ?
    Bill O'Neal WCM
    <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

  9. #9
    Joined
    May 2005
    From
    Detroit City
    Posts
    1

    Default Re: Rotary Valve Vs. Reeds

    Bill if you still have this set up I will take it off of your hands.

    Thanks
    Ben

  10. #10
    Joined
    Nov 2003
    From
    Glendora, CA
    Posts
    6,846

    Default Re: Rotary Valve Vs. Reeds

    Call me at 626 914 9509.
    Bill O'Neal <br>
    WCM
    <a href="http://www.watercraftmagic.com"

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