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26 posts in this topic

yes I know this is probably on here ten thousand times over but im lazy and dont feel like searching for it. so my question is I have a 1998 yamaha yz400f i curently run the highest i can get at the pump (91 octane no ethenol) and my bike always starts first kick no matter what and runs great so my question is could I run 87 that has up to ten percent ethenol in it, and my dad has an 83 suzuki pe175, could he also run  87 with no problems if not what would be the possible problems for both bikes.  and he started running synthetic snow mobile 2 cycle oil but is it worth it for 35$ per gallon vs 8$ a gallon for regular marine oil thanks btw he ran marine oil for 3 months but he did foul 2 plugs with marine oil and so far none with synthetic sled oil.

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I would definitely stick with at least 91 in the 400f. compression ratio is the biggest factor when choosing an octane rating. I think the yz400f has somewhere around 12.5:1 compression so you would probably notice a lot of spark knock on 87 or at the very least it will run hotter and have less power. My big bore 300ex has 11.5:1 and will spark knock on 91 but runs great on 93. I know comparing the 300ex to a 400f is like apples to oranges but that gives you an idea how much just 2 octane less can make. Im not sure about the compression ratio of the 175 but I would stick with 91 in it also. with the oil its the lubrication that matters. as long as your running the correct mix you should be fine using the marine oil. The synthetic typically does lubricate a little better and will burn cleaner but it is very expensive so if you've ran the marine oil and had good luck with it I don't see any problems with it.

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100 from the airport, probably 98 or so, by the time I burn it. I'm ported and polished so I gotta run high grade.

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Higher octane cools the combustion chamber more efficiently which translates into a little more power and better running. Nothing really noticeable though. Or so Mxa told its readers a while back, of course its main objective is fuels resistance to higher detonation, the higher the octane the higher the resistance to detonation. Yes I edited this post......

Edited by cr-dude3

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Would you guys choose 91 w/ethenol or 87 without?  Those are really my only two options around here.  Could go to the airport but thought 100LL was bad for your engine (lead).

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90 octane as labeled on gas pumps in the US and Canada meets the minimum requirement for all YZF models.  It equates to roughly 86-87 Motor Octane, or to about 95 Research Octane, as required by the manual.  91 is enough.  More than that, you're wasting money.

 

Higher octane cools the combustion chamber more efficiently which translates into a little more power and better running.

 

 

No, it does not.  Octane number is ONLY a measure of how well the fuel can resist being ignited by heat and pressure, rather than by a spark or flame.  In other words, detonation resistance. 

 

Octane number has nothing whatever to do with the vaporization rate (which does cool the cylinder), the burn temperature, burn rate, ignitability on exposure to flame, or the amount of energy the fuel releases when burned.  In fact it has nothing to do with any other aspect or attribute of the fuel, only the resistance to detonation. 

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90 octane as labeled on gas pumps in the US and Canada meets the minimum requirement for all YZF models.  It equates to roughly 86-87 Motor Octane, or to about 95 Research Octane, as required by the manual.  91 is enough.  More than that, you're wasting money.

 

 

No, it does not.  Octane number is ONLY a measure of how well the fuel can resist being ignited by heat and pressure, rather than by a spark or flame.  In other words, detonation resistance. 

 

Octane number has nothing whatever to do with the vaporization rate (which does cool the cylinder), the burn temperature, burn rate, ignitability on exposure to flame, or the amount of energy the fuel releases when burned.  In fact it has nothing to do with any other aspect or attribute of the fuel, only the resistance to detonation. 

 

Well ok.... I guess I'm dumb, ill go git some c-tane and run it in my scoot!

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C-tane is for Diesels.

 

Yeup, My brother runs it in his cummings engines at his truck driving school. It would burn a hole in a normal recip. engine.

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It would burn a hole in a normal recip. engine.

 

Not necessarily.  It's the wrong chemistry for gasoline fuels, but whether it would do any damage depends on the percentage added.  "C-tane" additive and others like it are the diesel engine parallel to octane boosters.  They are supposed to raise the Cetane number of the Diesel fuels, which is somewhat the reverse of octane number,  But, like gasoline octane boosters, none of them do very much, and the whole Cetane thing is off topic in this discussion and has no applicability one way or other.

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Not necessarily.  It's the wrong chemistry for gasoline fuels, but whether it would do any damage depends on the percentage added.  "C-tane" additive and others like it are the diesel engine parallel to octane boosters.  They are supposed to raise the Cetane number of the Diesel fuels, which is somewhat the reverse of octane number,  But, like gasoline octane boosters, none of them do very much, and the whole Cetane thing is off topic in this discussion and has no applicability one way or other.

You know your stuff, I am now learnid! I thank you.....

Edited by cr-dude3

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I run 91 octane pump gas in my bikes running 13:5:1 and 14:1+ plus compression.. bikes all run great and strong. 

 

I run 100LL (avgas) in my 450R that I race, which requires a remap on FI bikes, and re-jetting on carb bikes.

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90 octane as labeled on gas pumps in the US and Canada meets the minimum requirement for all YZF models.  It equates to roughly 86-87 Motor Octane, or to about 95 Research Octane, as required by the manual.  91 is enough.  More than that, you're wasting money.

 

 

No, it does not.  Octane number is ONLY a measure of how well the fuel can resist being ignited by heat and pressure, rather than by a spark or flame.  In other words, detonation resistance. 

 

Octane number has nothing whatever to do with the vaporization rate (which does cool the cylinder), the burn temperature, burn rate, ignitability on exposure to flame, or the amount of energy the fuel releases when burned.  In fact it has nothing to do with any other aspect or attribute of the fuel, only the resistance to detonation. 

This. Given the same content of oxygenate, a low to moderate compression engine that runs well on 87 won't run any better on 91. There are cars that advance timing as far as they can without knock (automatically), but minus fancy electronics like that, the higher octane doesn't matter. 

 

In some areas, higher octane fuel has less ethanol and that's a good reason to buy it. 

 

I run 91 octane pump gas in my bikes running 13:5:1 and 14:1+ plus compression.. bikes all run great and strong. 

 

I run 100LL (avgas) in my 450R that I race, which requires a remap on FI bikes, and re-jetting on carb bikes.

I wouldn't have expected 100LL to require different jetting but it may have to do with ethanol (you need more ethanol than gasoline, so running E10 in a bike set up for straight gas will be a little lean, and straight gas in a bike set up for E10 will be a little rich). 

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Do not run 87 octane in your YZ400F if you want it to last.  Your dad's old Suzuki might run OK on 87 depending on the compression ratio and overall condition, but if it's an air-cooled engine I would not risk it.  

Not sure why you are asking... if it's a money issue, just spend a few extra bucks and get the premium.  If it's an availability issue, sounds like you should stock up whenever you can, and use a stabilizer so the fuel stays fresh.

To answer your question on possible problems running 87 octane -- assuming you are riding the bike and occasionally going wide open with it:

Best case scenario could be a hot running engine, reduced power (with spark knock), hard starting when hot, maybe some funny smells.  

Worst case scenario could be damaged piston and piston rings, burned valves, motor oil thermal breakdown (maybe increased engine wear), broken spark plug (electrodes or porcelain), who knows what else.  

 

My 1999 YZ400F has the same engine as your 1998.  The sticker on the front fender says "premium unleaded gasoline only" or something like that (part of it is scraped off).  Around here premium is 91 octane -- the bike runs awesome every time and I often ride it hard.  I do run 87 octane through the YZF in the off season when the tank is dry -- just a few ounces funneled into the fuel line to fire it up and keep everything flowing instead of just letting it sit for months at a time.  There is no load on the engine and it is OK to run it for a few minutes on 87 octane this way.  

 

My XR400R will run on regular all day long, no problems.  It is a low-compression engine and I don't wring it out all the time, and of course it will run fine on premium too.  I think of the XR as a tractor and the YZF is a Formula race car.

 

Hope this helps you.

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Thanks @DGXR i think your post was the clearest out of all of them that's what I needed to know and again thanks

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Speaking of stabilizer. .. any suggestions on what kind to run? I'll probably be riding my trackbike infrequently enough that I should use some.

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