# Thread: Yamaha VX fuel experiment on top speed

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. totally agree ,my ski fzs is quicker on E10..

3. Cool assignment. what was the standard deviation?

4. Originally Posted by JordieS
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. Originally Posted by john belton
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.

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. 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.

8. 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. Originally Posted by CaptainReza
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. 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.