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  1. #1

    Yamaha VX fuel experiment on top speed

    Hello everyone,

    When I was a year 10 student (last year) I had to do a Science Research Project (SRP) so instead of doing something boring like how fast beans grow in different light conditions (my friend did that), I decided to see what fuel would make the Jetski go the fastest. Here is what happened:

    First I drained the tank of all fuel and then filled the tank with 5 litres of fuel. Then I did 6 full throttle runs on the same stretch of river (3 up and 3 down) and recorded the speeds with a GPS then wrote the speeds down and did again.

    On 98 RON my average speed of 6 runs was 87.3 kph
    On E10 (93-94 RON) my average speed of 6 runs was 88.2 kph
    On regular unleaded (recommended fuel) (91 RON) my average speed of 6 runs was 87.7 kph

    Fastest speed on the day was 89.1 kph on E10

    It was a fun experiment and just thought I'd like to share the results with all of you.


  2. #2
    billy's gpr's Avatar
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    totally agree ,my ski fzs is quicker on E10..

  3. #3

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    Cool assignment. what was the standard deviation?

  4. #4
    Quote Originally Posted by JordieS View Post
    Hello everyone,

    When I was a year 10 student (last year) I had to do a Science Research Project (SRP) so instead of doing something boring like how fast beans grow in different light conditions (my friend did that), I decided to see what fuel would make the Jetski go the fastest. Here is what happened:

    First I drained the tank of all fuel and then filled the tank with 5 litres of fuel. Then I did 6 full throttle runs on the same stretch of river (3 up and 3 down) and recorded the speeds with a GPS then wrote the speeds down and did again.

    On 98 RON my average speed of 6 runs was 87.3 kph
    On E10 (93-94 RON) my average speed of 6 runs was 88.2 kph
    On regular unleaded (recommended fuel) (91 RON) my average speed of 6 runs was 87.7 kph

    Fastest speed on the day was 89.1 kph on E10

    It was a fun experiment and just thought I'd like to share the results with all of you.
    Interesting. I have heard people make similar claims but have never seen it documented like you have done here. Do you, or anyone else, know why this is?

  5. #5
    hitman's Avatar
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    Quote Originally Posted by john belton View Post
    Interesting. I have heard people make similar claims but have never seen it documented like you have done here. Do you, or anyone else, know why this is?
    Because the results are going to be different for every type of ski that has a different tune in it. If you have a tune that is designed to or requires the higher octane then of course you are going to get better results by using that specific fuel.

    If my ski is tuned for regular 87 octane and I throw in 93, it's not going to make a bit of difference because I didn't add any extra timing in the tune to take advantage of the increased octane. The timing and tune is what is going to give you noticable speed and performance increases. Higher quality fuel is only necessary to get that added performance safely. It's not exactly what gives you the increase.

  6. #6
    jetpilot785's Avatar
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    Alot of it has to do with fuel burn rate as well. Higher Octane has a slower burn rate therefore you can add compression and/or boost and safely run it where as lower octane has a faster burn rate and lower compression and/or boost is required as too high of compression and/or too high of boost will cause the fuel to ignite prematurely (pre-ignition) and instead of burning at a high rate of speed, it will explode causing detonation which will cause damage over time depending on how bad the detonation is. Most engines will run their best when they are on the ragged edge of detonating but it doesn't mean it is recommended or safe for the engine to operate at those levels. I don't know how your fuels are rated over there and what they use for ingrediants but something else to keep in mind is fuel addatives. Some fuels have additives like ethanol which helps to oxygenate the fuel for a cleaner and more complete burn. I don't know much about the fuels you used for your test but the E-10 may have ethonal in it which would make sense as to why your ski picked up power and speed in your test. As far as the other fuels, the regular unleaded may not have ethanol in it but it will be a good safe fuel to run as it is the recommended fuel and the 98 RON may have too slow of a burn rate for the compression ratio and cylinder pack on your NA engine and it isn't getting as complete of a burn and you actually waste fuel when the burn cycle is not completed. If you took the experiment farther, you would probably find that the regular unleaded would get the best mileage of the 3 as it would not need additional fuel to compensate for the ethonal. The E10 would sit in the middle as the burn rate is more complete than the 98 RON but due to the added oxygen levels from the ethonal, it would have to throw more fuel at it to compensate for proper AFR's and the 98 would be the least economic fuel as it won't be able to burn as much and the unburned fuel will be expelled through the exhaust and to maintain similar performance levels, the throttle position would be in a more advanced position as the 98 would need more aggressive throttle to maintain the power level of the lower octane and ethanol blended fuel.

    There are alot of people who don't understand fuels and they think octane makes HP and it does with the right combinations but an engine set up for pump gas runs worse on race fuel so I like when people show up to race someone and they brag they put race gas in there tank on a low compression engine. The only thing it does is makes it smell nicer and most will agree race fuel smells good!

  7. #7
    Thank you everyone for your replies, I found in my research the things that jetpilot785 has said. The higher octane the fuel the less energy it has in it which is why it resists detonation and burns slower, so putting higher octane fuel in an engine not designed for it doesn't make it more powerful/faster.

    It would be interesting to see this test done on another ski with regular unleaded compared to E10, but since it is an oxygenate like jetpilot said maybe it does make a cleaner burn and more power.

    It's a shame I've haven't put E10 in the ski in a while, if I do now it might clean the sludge from the tank and block up my filters.

    Thanks for reading everyone.

  8. #8

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    Yes, jetpilot said it correctly!

    Premium gas is not going to make your engine perform better if your engine is designed for regular gas! Basically it is waste of money, no performance gain! Now you put regular gas in high performance/high compression engines, you can cause all kinds of issues including pinging as fuel ignites before TDC is reached!

    That being said, I am still amazed how Yamaha with 12.9:1 or was it 11.9:1 compression recommends only regular gas! BMW has near that compression and you will need higher octane gas!

  9. #9
    YoYamma's Avatar
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    Quote Originally Posted by CaptainReza View Post
    That being said, I am still amazed how Yamaha with 12.9:1 or was it 11.9:1 compression recommends only regular gas! BMW has near that compression and you will need higher octane gas!
    Another Yamaha benefit;
    you won't get that from Sea-Doo or the Ultra junk coming out of Kawi...

  10. #10

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    A single instance of your maximum speed from each scenario is not going to be the most accurate measurement of delta between your samples. What was your median, average, and standard deviation for all of the sample groups?

    Those measurements will give you a better grasp on what you accomplished. And of course, the larger the sample size the more accurate you will be. This is assuming other environment variables remained fairly constant ( water temp, surface condition, engine temp, wind, etc).

    If you wanted to post your sample data up, we could see how much they vary.

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