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  1. #1

    Blow Off and Air Bleed Valves

    I think a dialog about the 2 intercooler relief valves would be helpful.

    There are 2; a "relief, air bleed" valve and a "relief, blow off" valve (see Kawi parts diagram on their site). The first is most visible on the front of the intercooler and has a small line to the intake manifold (vacuum or pressure depending on intake conditions but I think only vacuum matters for valve operation).

    The second (blow off) is on the back side of the intercooler and has no signal line - just an input from the intercooler and a low pressure ribbed outlet to the air box (the outlet is the same as that on the air bleed valve).

    From the Kawi web site:
    " To prevent over boosting at low and medium rpm, two different air bypass valves are used
    - The smaller air bypass valves releases low amounts of excess pressure build-up, for precise boost management
    - The larger air bypass valves is used when excessive boost pressure is accumulated, to maintain an even intake pressure even when giving full-throttle from idle"

    This seems like a poor explanation that I welcome clarification on.

    My take from looking at the engine is the "air bleed" is to prevent compressor surge and severe over-boost, e.g. when running at full throttle, full RPM and cutting the throttle. I think this because it appears to be a vacuum assisted (operated?) valve that would get a strong vacuum signal when the throttle is cut.

    The "blow off" valve seems to be the boost limit control (waste gate).

    Importracer seems to have the best posts on this subject so far. He has apparently blocked off the blow off valve and gotten about a 1.5 psi increase in boost pressure.

    He questions why both valves are needed. As do I. I would think either could possibly do the job. The blow off valve would seem to be the best single choice as relying on the air bleed valve requires that there are other restrictions on ultimate boost - e.g. air flow restrictions (intake, exhaust or supercharger flow limitations).

    Importracer's results imply, however, that there are such flow restrictions and that relying on the air bleed valve does control ultimate boost to a somewhat higher (but within spec) level - leaving the air bleed valve to control surge and off-throttle over presuure.

    My interpretation would agree with the Kawi site if 2 things changed first, if they referred to going from full throttle to idle at the end of the description of the larger air bypass valve rather than the opposite. And second, if they mentioned that the smaller bypass valve is apparently never needed except to cheat us out of the 11.4 psi boost they advertised and to replace it with 10 psi.

    Comments and corrections welcomed.
    Last edited by DaveF; 03-12-2007 at 10:20 PM. Reason: typo


  2. #2
    Importracer seems to have the best posts on this subject so far. He has apparently blocked off the blow off valve and gotten about a 1.5 psi increase in boost pressure.
    He's also running lean. Without the fuel programmer then the engine has more air without more fuel. PROBLEM.

    The biggest reason why no one is talking of the Valves is because we dont have the resource yet to change fuel. Why mess with it till we can get more fuel to match the extra boost.


    If ya like once my computer is installed the Ill also block the valve and give you the A/F range from doing the block off. Im working on the wiring.

  3. #3
    R rated's Avatar
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    yes you can cap off but in our testing found the EGTs to go up ! must add more fuel ! we will be doing a lot more testing on this very soon .
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  4. #4
    Importracer's Avatar
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    Quote Originally Posted by Skips313 View Post
    He's also running lean. Without the fuel programmer then the engine has more air without more fuel. PROBLEM.

    The biggest reason why no one is talking of the Valves is because we dont have the resource yet to change fuel. Why mess with it till we can get more fuel to match the extra boost.


    If ya like once my computer is installed the Ill also block the valve and give you the A/F range from doing the block off. Im working on the wiring.
    Please explain! Have you ever had a forced induction motor of any type other that this ski? If the factory boost level is 11.4 and I am only seeing 10 then either the spring is weak or their info is not correct. Since my boost level is now at the "factory" level HOW am I running lean. Have you checked the MAP sensor to determine at what boost level the sensor voltage is pegged?

  5. #5
    If your only geting 10 lbs of boost then why dont you take it back to the dealership under warrantee. Why alter it. Others have done as you have done and found that the EGT temps go up and the AF level go lean.

    Look Im just warning you. If you feel that you have extensive knowledge from other motors then by all means do as you know best. I was only trying to save you from a bad situation but its obvious you know what your doing.

    You may also think about running a A/F sensor before you go blindly moding the boost. Just my .02 cents.
    Last edited by Skips313; 03-13-2007 at 07:33 AM.

  6. #6
    Importracer's Avatar
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    Quote Originally Posted by Skips313 View Post
    If your only geting 10 lbs of boost then why dont you take it back to the dealership under warrantee. Why alter it. Others have done as you have done and found that the EGT temps go up and the AF level go lean.

    Look Im just warning you. If you feel that you have extensive knowledge from other motors then by all means do as you know best. I was only trying to save you from a bad situation but its obvious you know what your doing.

    You may also think about running a A/F sensor before you go blindly moding the boost. Just my .02 cents.
    And at what boost levels did they start seeing a rise in EGTs? I doubt it was at 11 lbs. I already have a wide band going on the ski, I am making an threaded adapter so I can plug the bung when I want to remove the sensor. Thanks

  7. #7
    R rated's Avatar
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    on our test Ultra the boost gauge (stock) said one bar over 10 psi on the system we are using to test with it showed 11.4-11.5 ,When it was colder the next morning the system showed 11.6- 11.7 .and also we do have 02 sensors Too, will be doing much more testing soon !

  8. #8
    OK sorry, just trying to help ya out.
    Im not the one to know but I am constantly talking with those that do. All have suggested not doing anything to the boost untill you can alter the fuel system.

  9. #9

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    Most would be happy if it didn't back down on top.
    While we wait on the fuel controllers that are on websites in pictures.

  10. #10
    Once again I say in friendly manner. You will most definatly want to wait for the fuel programmer to be released before adding boost to your boat.

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