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Thread: 2 strokes and race gas

  1. #1
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    Default 2 strokes and race gas

    So I have done some research and it seems to me that using race gas in a 2 stroke might be overkill (maybe even detrimental to performances).
    Of what I understand, race gas is good for high compression engines, which 2 strokes do not have.
    So maybe I should even run the lowest octane gas I can find...

    Did I get things right?
    Lewis a.k.a. Frenchie a.k.a. Hey You!
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  2. #2
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    IIRC my YZ250 manual calls for at least 95 octane. It runs alright on 93, but when I cut Sunoco super 112 octane 50/50 with 93 it runs ten times better. Not much more power, but the motor is definitely happier.
    06 DRZ400S
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  3. #3
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    Do you think it would be the same for a smaller engine (85cc)?
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
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    Nobody else?
    Lewis a.k.a. Frenchie a.k.a. Hey You!
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  5. #5
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    run the highest octane you can find in your two stroke. make sure the engine is jetted appropriately for race gas though. DO NOT run low octane
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  6. #6
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    Well, I guess I will get 93 from now on. I can't fit a $10 gallon of gas in my budget...
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
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    Neither could I, that's why I usually got it from the local circle track for way less that VP usually ran and cut it half and half with 93.
    06 DRZ400S
    08 Yamaha YZ250 two stroke that I need to sell...

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    Quote Originally Posted by Rob.hall View Post
    Neither could I, that's why I usually got it from the local circle track for way less that VP usually ran and cut it half and half with 93.
    Good thinking. I will try.
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
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  9. #9
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    The benefits of race fuel are consistency and the lead content of leaded fuels is a excellent lubricant. The problem with a 2-stroke is it's sometimes hard to hear if it's pinging or detonating.

    I run a 50/50 mix of C12 and pump 93.

    A less expensive option would be to pick up some 100LL from a local airport. I think it's about $5-6 gallon right now.
    Last edited by Toadmeister00; 04-18-2011 at 05:11 PM.
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  10. #10
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    That might be the national average, but I seem to remember taxiing by the pumps recently and it was under 4 bucks... Depends on the airport though.
    06 DRZ400S
    08 Yamaha YZ250 two stroke that I need to sell...

  11. #11
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    i have 111 octane out of the pump avaliable here so im lucky but in all my bikes 2 or 4 stroke i run about a 50/50 mix of 111 and 93 octane...

    if u do som elooking around you can fine around 110 octane from the pump way cheaper than VP... theres alot more around than you think...
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    Quote Originally Posted by Rob.hall View Post
    That might be the national average, but I seem to remember taxiing by the pumps recently and it was under 4 bucks... Depends on the airport though.
    I was just going by this: http://www.100ll.com/

    I know it was $4ish last year in VA. Not sure now with the hike in fuel prices again.
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  13. #13
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    To get the best out of race gas on your yz85 (assuming your talking about the bike in your sig) get the head re-profiled for higher compression, or buy a high compression head (vhm, bud etc..) and then it will only run well on race gas, but it will go faster, not sure how much extra power but the will be an improvemnt (wether noticeable or not I dont know)
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    Default

    4-stroke or 2, doesn't octane-suitability depend on compression-ratio? And in a 2-stroke is it not the port-heights, head volume (lower the volume = higher the CR), and squish that determine what the compression ratio is? And since using a chamber bumps up the dynamic compression ratio big-time, I don't think 95 octane will be overkill for most of the modern 2-strokes... no idea about race-gas though... we don't get that here very easily :-(

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    Quote Originally Posted by george8 View Post
    To get the best out of race gas on your yz85 (assuming your talking about the bike in your sig) get the head re-profiled for higher compression, or buy a high compression head (vhm, bud etc..) and then it will only run well on race gas, but it will go faster, not sure how much extra power but the will be an improvemnt (wether noticeable or not I dont know)
    Thanks for the tips. I won't touch the engine before a looooooong time. I have more to gain by changing my suspensions and riding for now. However, I will try to mix some higher octane gas, just to try...
    I will keep that in mind though
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
    SMUSA #666

  16. #16
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    Wise words about suspension, you can have all the power in the world, but without a decent suspension set up you aint going to win any races
    KTM Duke 640
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  17. #17
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    I would HIGHLY recommend getting the head machined. It will just make the bike more efficient.

    Tell the tuner what you are doing with the bike. For these things we want tight squish but LOW compression. High compression on a 2-stroke helps bottom end torque but hurts the over-rev on top. The good tuners will machine the face and the squish band to get the squish right, then machine the bowl to change the shape and volume. You can get it done for about $75 or less.
    2004 KTM 65 Endurance Racer "Project 65/85"
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  18. #18
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    Quote Originally Posted by Toadmeister00 View Post
    I would HIGHLY recommend getting the head machined. It will just make the bike more efficient.

    Tell the tuner what you are doing with the bike. For these things we want tight squish but LOW compression. High compression on a 2-stroke helps bottom end torque but hurts the over-rev on top. The good tuners will machine the face and the squish band to get the squish right, then machine the bowl to change the shape and volume. You can get it done for about $75 or less.
    I have no clue what you are talking about (squish and face, and all... ) but I will sicky that thread for future use.
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
    SMUSA #666

  19. #19
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    Quote Originally Posted by Judaslefourbe View Post
    I have no clue what you are talking about (squish and face, and all... ) but I will sicky that thread for future use.
    "Squish" is the distance from the piston to the head at the very outside of the piston edge. Getting the squish set properly is "2-stroke Tuning 101" and the first step to a strong-running, efficient machine. You can have the head set up for either pump or race fuel.

    Either one of these two guys will get you set up.

    http://www.rb-designs.com/

    http://www.cycleplayground.com/index...id=14&Itemid=7
    2004 KTM 65 Endurance Racer "Project 65/85"
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  20. #20
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    Quote Originally Posted by Toadmeister00 View Post
    Awesome! Thanks for the links!
    It is way cheaper than I expected. Hopefully next season....
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
    SMUSA #666

  21. #21
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    One of the things I love about two strokes, everything is MUCH cheaper than their 4t counterparts.
    06 DRZ400S
    08 Yamaha YZ250 two stroke that I need to sell...

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    Quote Originally Posted by Rob.hall View Post
    One of the things I love about two strokes, everything is MUCH cheaper than their 4t counterparts.
    Sort of...the smokers get you a little more at a time. Mine are THIRSTY! Fuel and oil costs add up when using race fuel and high dollar premix.

    Hard parts (cylinder, head, piston, etc.) are still expensive if you have catastrophic failures.

    That's why I run good gas, good premix and a lot of it, way rich on the jetting and hope for the best.
    2004 KTM 65 Endurance Racer "Project 65/85"
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  23. #23
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    Default 100LL avgas

    run it in 50, 65, 125 KTM two-strokes. They LOVE it. 40-1 motul.
    Tried it in XR650R and 525SX, not so much.

    Didn't have to rejet the little KTM's - they are race mod motors. The 125 needs to be rejetted to really get the most out of the fuel.

  24. #24
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    Two strokes use a different formula to determine compression ratio, so the numbers are misleading when compared to four strokes. The compression is every bit what the four strokes run if not more.

  25. #25
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    Quote Originally Posted by Rob.hall View Post
    One of the things I love about two strokes, everything is MUCH cheaper than their 4t counterparts.
    Amen: I am redoing the top end: $85 with shipping
    Lewis a.k.a. Frenchie a.k.a. Hey You!
    YZ85 '05 - Why do I ride minis? Because I don't need to compensate for anything!
    RMZ250 '07 - Engine exploded (twice!)
    450SMR '06 - OMAGAD! OMAGAD! OMAGAD!
    SMUSA #666

  26. #26
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    Quote Originally Posted by Judaslefourbe View Post
    Amen: I am redoing the top end: $85 with shipping
    If you've got it apart its crazy not do a solder test and get the head done.
    See the RB site for the solder test specifics.
    2004 KTM 65 Endurance Racer "Project 65/85"
    2004 KTM 105 Supermoto

    www.tdc2strokeperformance.com
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