When to run race fuel?
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  1. #1
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    When to run race fuel?

    I have been given, what I consider, some pretty solid advice from some folks stating that using the screw on compression testers is not the best way for figuring out if you need to run race fuel. It sounds as if figuring out exactly what your compression ratio is, is the best way to go. I have found a number of good videos that will help me determine this, but my question is what compression ratio then determines the step up from say 92 octane to 100? If this is all wrong, please state why and thanks!

  2. #2
    Attention ***** PWCToday.com Is My Home Away From Home JonnyX2's Avatar
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    Re: When to run race fuel?

    Even if you had marginal compression and ran a crazy advanced timing curve you may need race fuel. There is more to the equation than just compression. You may not get a straight answer because of so many variables in watercraft. Compression, squish clearance, timing, impeller pitch (engine load) all play a part in fuel octane requirements.

    That being said I will let the experts give their advice!
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  3. #3
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: When to run race fuel?

    They just did.

  4. #4
    Top Dog jobrown's Avatar
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    Re: When to run race fuel?

    Subscribed! I just tell Chris at Newmiller what gas I want to run and send my head to him and let’s him do it... that being said he always talks timing and what it should be set at.




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    Re: When to run race fuel?

    Subbed as well.

    I asked similar questions about calculating compression ratios such as 12 to 1 and compared to compression psi ratings, and fuel type not too long ago.

    I would think most of us rec riders, are not changing timing much, but mainly just changing to aftermarket heads. When were talking the affects of timing, were talking about port/exhaust gas/scavenging timing or spark timing? Both?


    Sent from my iPhone using Tapatalk

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    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: When to run race fuel?

    You should have determined the compression ratio while building the
    engine.


    So, why are considering race gas now? Did the engine stop, and restart
    after a wot run?

    Quote Originally Posted by JonnyX2 View Post
    There is more to the equation than just compression. You may not get a straight answer because of so many variables in watercraft.

    Compression, squish clearance, timing, impeller pitch (engine load) all play a part in fuel octane requirements.
    ++1

    We need more details, set-up, and background on why you are interested
    in race gas?


    Bill M.

    Quote Originally Posted by Couchrider View Post
    but mainly just changing to aftermarket heads.
    There are a few bad heads and head gaskets for the Kawasaki 650.

    Unfortunately a lot of used performance products are parts what I
    call "shelf parts." Often parts that worked poorly, were put on a shelf,
    until someone who doesn't know why it was put on the shelf sells
    the parts.
    Last edited by wmazz; 08-31-2018 at 12:41 AM.
    Horsepower == Speed, RPM != Speed



  7. #7
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    Re: When to run race fuel?

    Quote Originally Posted by wmazz View Post
    You should have determined the compression ratio while building the
    engine.


    So, why are considering race gas now? Did the engine stop, and restart
    after a wot run?



    ++1

    We need more details, set-up, and background on why you are interested
    in race gas?


    Bill M.



    There are a few bad heads and head gaskets for the Kawasaki 650.

    Unfortunately a lot of used performance products are parts what I
    call "shelf parts." Often parts that worked poorly, were put on a shelf,
    until someone who doesn't know why it was put on the shelf sells
    the parts.
    Well was trying to keep this simple but... I am not considering race gas, I am trying to get out of using it. I have been using it for quite some time as I used to race (over 20 years ago) and had both my Kawasaki 750SX's modded up quite a bit. I believe Chris Newmiller is the one that was explaining he does not trust compression testers and that you need to measure the motor precisely as you mention, preferably while building the motor. But... There is a way to measure after that fact. Here is how. https://www.youtube.com/watch?v=PZPp...3sZLdYeg&t=25s

    I was thinking about sending to Chris and had a discussion with him on the phone about it, but I believe he is up in Oregon and I am in California and taking everything completely apart and sending it up that way was not a great option, as I have two skiis and they are both in working order.


    I have since done a few changes to my skiis in an effort to make them easier and more manageable to Rec ride.

    Mod ski -

    Removed MRD fuel injection, Total loss ignition and lightened (non-charging) flywheel). Moving my Super Stock Mikuni46 Racing Green Specialty carb over to this ski.

    Existing things about this ski. Group K Hammer kit on the engine. Jet Pro pipe. Ocean Pro Swirl head (which unfortunately cannot be altered), other usual goodies


    Super Stock Ski -

    Removing 46 carb and installing just rebuilt dual 44 Mikuni's. Factory Pipe and other normal goodies.

    Thanks for any feedback guys! I am rusty at best on jetski work and did not do the best job of documenting all details to my skiis back in the day.

  8. #8
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    Re: When to run race fuel?

    @couchrider did you get any answer regarding fuel type to compression ratio? I don't want to use race fuel anymore, but obviously need to make sure I can before doing so, as I don't want to ruin my motors.

  9. #9
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    When to run race fuel?

    I kinda got the same answers here, mostly what I took away from it was its better to build an engine with a target in mind rather then try to work it out after you put parts together. But basically from what I gathered around the net 12:1 was good for premium. Now that doesnt take into account the timing and pipe. If you bored over and changed head compression and running a stock timing ignition and stock exhaust Id say 12:1 on premium. Bored, head, performance exhaust? Consult an experienced builder. Although Id try to find something to buy from the builders company, I dont like to ask them for their hard earned knowledge while they are trying to feed their families off of a business that is a niche market, their not getting rich off us lol.


    Also Id like to add I am no way shape or form an experienced builder. Just passing along info I gathered, before taking my advice please check with a pro.

    Sent from my iPhone using Tapatalk
    Last edited by Couchrider; 08-31-2018 at 02:11 PM.

  10. #10
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    Re: When to run race fuel?

    Quote Originally Posted by Couchrider View Post
    I kinda got the same answers here, mostly what I took away from it was it’s better to build an engine with a target in mind rather then try to work it out after you put parts together. But basically from what I gathered around the net 12:1 was good for premium. Now that doesn’t take into account the timing and pipe. If you bored over and changed head compression and running a stock timing ignition and stock exhaust I’d say 12:1 on premium. Bored, head, performance exhaust? Consult an experienced builder. Although I’d try to find something to buy from the builders company, I don’t like to ask them for their hard earned knowledge while they are trying to feed their families off of a business that is a niche market, their not getting rich off us lol.


    Also I’d like to add I am no way shape or form an experienced builder. Just passing along info I gathered, before taking my advice please check with a pro.

    Sent from my iPhone using Tapatalk
    The mod ski was bored, yes with a Group K Hammer kit. I made the major mistake though of removing the stock head that they modified with this Ocean Pro head just to bump compression. I know super bad idea, I was young and dumb and someone traded me, so I no longer have that stock head! This ski runs an after market pipe from the now defunct JetPro. I love this pipe though and it sounds so good!

    I think both skiis were bored just out of necessity from wear and tear.

    I agree with you on purchasing from these builders. Does anyone know anyone in Northern California? I think there is one over in Antioch maybe?

    My goal is to get these skiis running well just to go have some fun and then hopefully sell them, so I can buy myself a new ski!

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