Thoughts on 93 octane.

[blairwill4]

So I run 93 octane in my 96 xp. Is this a bad idea? I just always thought it was a cleaner more efficient fuel, so why not use it to help keep the carbs and other components clean? Should I only be using 89 on my ski?

My ski is pretty much stock except for a solas impellar,(couldnt tell you the pitch), and a jet dynamics intake grate.

 

[Spimothy Leary]

IMO 93 is not necessary, you'll need 93 when you put a factory pipe on.. but not yet.

 

[blairwill4]

Well thats good to know considering Ive been looking for a factory pipe. But I only paid 700$ for my ski I cant justify paying the same for an exhaust lol.

 

[SabrToothSqrl]

good price for that ski!

93 octane actually has LESS power per gallon (energy) than 87.

so unless the engine is designed to use higher octane (yours is not) you are not only wasting money, but actually reducing HP.

 

[get_real]

I'd assume that is premium high-test gas, from what I've been told here in the south most premium gas does not have ethanol. That can be a good choice when filling up off the water as marine gas is ethanol free. Less chance of moisture in the fuel system and better for the rubber componets.

I did a little more research and it sounds like the ethanol free premium is not universal. Guess you'd need to do some research in your state to validate that. Since ethanol is used to increase the octane (knock resistance) then it would seem they would use it in higner octance fuels.

 

[blairwill4]

I got a steal on my ski. Drove 3 hours into michigan to get it back in january. SBT motor thats still under warranty and supposedly had like 6 hours on it. Not it has probably close to 15. So I guess Ill run a tank of 87 and see if I like it better then hmm? It doesnt do anything for keeping the fuel system clean??



This is my ski

 

[SabrToothSqrl]

I'd assume that is premium high-test gas, from what I've been told here in the south premium gas does not have ethanol. That can be a good choice when filling up off the water as marine gas is ethanol free. Less chance of moisture in the fuel system and better for the rubber componets.

Good theory; however 'premium' is a marketing term.

Ethanol is also used to raise the octane level in fuel... so 93 may have more of a chance of having ethanol in it.

I hate ethanol as well.

have you seen www.puregas.org

these skis don't seem to mind 10% long as you've replaced the grey fuel lines.
Don't mind, but I'd prefer real gas if I could get it! More Power per gallon = more HP.

I believe you can take a sample of fuel, put it in a sealed container. Add some water. Mark the line of separation. come back in a few hours, and re-check the line. If it's moved up, the fuel contains ethanol that has now absorbed water. (hence why your marked line is now too low on the container).

of course I don't want to get on my soap box of how much I hate ethanol... but there are some great youtube vids as well:

I can't find the video but it explained just how much of a failure ethanol is...

http://www.youtube.com/watch?v=gsSQSuCiUjE

ethanol test video

You can bet all manufactures test their HP ratings on PURE gas as well.

 

[get_real]

Good theory; however 'premium' is a marketing term.

Ethanol is also used to raise the octane level in fuel... so 93 may have more of a chance of having ethanol in it.

I hate ethanol as well.

have you seen www.puregas.org

these skis don't seem to mind 10% long as you've replaced the grey fuel lines.
Don't mind, but I'd prefer real gas if I could get it! More Power per gallon = more HP.

I believe you can take a sample of fuel, put it in a sealed container. Add some water. Mark the line of separation. come back in a few hours, and re-check the line. If it's moved up, the fuel contains ethanol that has now absorbed water. (hence why your marked line is now too low on the container).

of course I don't want to get on my soap box of how much I hate ethanol... but there are some great youtube vids as well:

I can't find the video but it explained just how much of a failure ethanol is...

http://www.youtube.com/watch?v=gsSQSuCiUjE

ethanol test video

You can bet all manufactures test their HP ratings on PURE gas as well.

Agree, I was editing my post while you were typing yours. I think ethanol in theory was a good idea, but not so sure it's good in execution. Whether it's helping the planet is debatable, but the harm it does to gas operated machines is not!

 

[Spimothy Leary]

Well thats good to know considering Ive been looking for a factory pipe. But I only paid 700$ for my ski I cant justify paying the same for an exhaust lol.

lol...

it appears the others agree with me on the octane, so after 3 years of using 87, you'll have enough to afford a factory pipe.

but your quotes on the FP are a little high... I think they run about $350ish.... they don't come up all that often, but when they do, i think the going rate is in the mid 300's... and at that time i'd add prok's and rejet, (another $120) but patience... enjoy the ski for now....

 

[blairwill4]

I cant find any used ones. 700 is what I see for new. 57 will be fast enough for now lol.

 

[Spimothy Leary]

I cant find any used ones. 700 is what I see for new. 57 will be fast enough for now lol.

honestly, i think it is... i had pipe, prop, nozzles, flame arrestors, and I could only get mid 61.... but... I did get there pretty god dam fast....

 

[blairwill4]

Lol thats wear im at. On a small ski its not how fast you go its how quickly you get there. With the new wear ring ive got and the prop and intake grate Im pretty happy with what I got for what those things cost. Lined up against 2 of my buddies this weekend both with 96 xps pretty much stock and I pretty much walk them off the line. Quick is what makes it fun especiialy when jumping

 

[Strizzo]

good price for that ski!

93 octane actually has LESS power per gallon (energy) than 87.

so unless the engine is designed to use higher octane (yours is not) you are not only wasting money, but actually reducing HP.

not true, unless you're comparing 87 octane straight gas to 93 with ethanol, as ethanol has a lower power density than straight gas. I buy 91/93 because it tends to not have ethanol or at least not as much. the advnatage of higher octane is that it is more stable, and so is less prone to detonation in high temp, high compression applications. this allows a tuner to advance the spark timing more, resulting in more of the burn happening earlier in the cycle, which allows the combustion chamber to capture more of that burn before the exhaust port is uncovered in a 2-stroke application, or before the exhaust valve opens in a 4-stroke.

even if you don't have the ability to adjust timing to take advantage of the added detonation protection of 93 octane, as long as your engine is in good working order it shouldn't hurt performance to run it, and if you have a carb issue and run lean or when you're running out of gas it gives a bit of extra protection.

 

[SabrToothSqrl]

Nope. It is. 87 octane contains more energy per gallon than 93.

Your adding things to raise octane. Regardless of their chemical make up, you are displacing fuel.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand fuels of higher octane. A common misconception is that power output or fuel efficiency can be improved by burning fuel of higher octane than that specified by the engine manufacturer. The power output of an engine depends in part on the energy density of the fuel being burnt. Fuels of different octane ratings may have similar densities, but because switching to a higher octane fuel does not add more hydrocarbon content or oxygen, the engine cannot develop more power.

I'll find the exact link later, but read, read, read

http://en.wikipedia.org/wiki/Octane_rating

I am only talking about the FUEL. Not how it's used. There was a similar thread here last season too.

An engine can derive more power from a higher octane IF and only if it has been designed for it. (High compression).

https://en.wikipedia.org/wiki/Gasoline#Octane_rating


Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where octane is raised by blending in ethanol, energy content per volume is reduced.
http://www.princeton.edu/~achaney/tmve/wiki100k/docs <-- link cut off on my ipad

http://physics.info/energy-chemical/

Note that aviation fuel (higher octane) has less energy.

No worries, it's a quite specific statement. My buddy owns a 28 foot race boat with a 525. On the dyno it's almost 40 more HP on 87 than 93. It's just not a high-compression engine. If it was, it would generate more power with a higher octane. Stock class. You are not allowed to modify anything or open the block.

But yes, for tuning purposes, and tweaks, 93 will reduce knock. However a properly tuned engine, designed for 87, will run best, on 87.

Anyone have a dyno we can slap a seadoo engine on and test all this?!

 

[blairwill4]

Anyone have a dyno we can slap a seadoo engine on and test all this?!

RIGHT?! it would be interesting to see if all these 787s really put out that 110 horse.

 

[Strizzo]

Yes, you are adding things to reduce detonation potential, but those additives do not have zero energy content, and are usually petro products themselves. Your quote says "where ethanol is used to increase octane rating, energy content is reduced" which is what I said, as ethanol has a lower energy content per volume. Also, these engines are no bbc, and when the tuned pipe kicks in it is a lot like forced induction.

 

[skewba98z28]

I've ran 87 octane with fuel that may contain up to 10% ethanol according to the sticker on the pump in a 657, 717, 787, and 787 RFI with ZERO issues. I don't baby my skis either.