I've decided to create this thread due to an overwhelming amount of "what octane" threads and misinformation.

For those who insist on using premium, if it makes you feel better or if its a sense of assurance go for it.

First of all Honda would not risk a potential hundreds of thousands of dollars if not more in waranty work and publish 86 octane for no reason. They are the largest engine manufacturer in the world and the largest motorcycle manufacturer in the world. Honda has been known for extensive R&D before releasing something into the market. This is the exact reason i trust Honda automobiles and motorcycles.

Second. For those who use the compression ratio arguement, this is only a fraction of the story. Its kinda like saying a 8 ounce salmon filet has just as much fat as a 8 ounch steak. One is an abundant source of omega 3 fatty acids which is good, the other is full of saturated fats. Sure the compression ratio is 12.0:1 but thats a very very generic figure. How is this generic you may ask. 12.0:1 is a static figure and only factors the volume with the piston at bottom dead center divided by the piston at full compression aka top dead center. A very simple explaination to this would be this. Say we have a 4 cylinder engine with a total displacement of 2000cc's, each cylinder displaces 500cc's. the combustion chamber in the cylinder head displaces 50cc's. 500 divided by 50 equals 10, in other words a 10.0:1 compression ratio. so just like my analogy to fat content in salmon and steak, static compression ratio is insignificant.

In the bigger picture we would see the pistons moving up and down, rod ratios, intake and exhaust valves opening and closing, valve overlap, and of course the static compression ratio. Dynamic compression ratio factors in all of the above, a much more complex calculation. a typical dynamic compression ratio for a pump gas motor would most likely be in the range of 7.5 to 8.5:1. with stock or street cams this would typically translate to a 10.0 to 12.0:1 static compression ratio. Of course more info would be needed for an exact figure.

Even more complex is detonation (aka pre-ignition,ping, or knock). Detonation is the burning of the air fuel mixture in a volitle and uncontrollable manner creating a violent spike in cylinder pressure. In ideal conditions the air fuel mixture will burn in an even and controlled fashion. The higher the octane the lower the energy content (british thermal units) which results in a better the resistance to detonation. The higher the compression ratio the less resistant the engine will be towards detonation. Again this is only half the story. Detonation is also determined by the temperature of the ambient air entering the engine, temperature of the engine components, air density, engine load, combustion chamber design, engine speed as well as gasoline octane and compression ratio.

Yes i am a noob... to the forum. However i have much experience in the motorsports field. This thread was not meant to offend anybody.

Sticky material?

I've been argueing that side till I was blue in the face... it's a good post.

The thing that most people don't get is the relationship between preasure and tempature... you didn't explicitly state it, however, I knew from your post you understood it.

Amonton's law.
Preasure (low compression)/ Temp (low compression = Preasure (high compression) / Temp (high compression)

You quirt in cold gas, into a low preasure system (old carb bikes really were a mini-vacuum, that's how they worked) - and then you preasurize it incredibly. In so preasurizing it the tempature goes up proportionally. In english - if it was cold and low preasure, it's now hot and high preasure.

Gas has a flash point. If you reach that tempature it goes boom. Well that's a bit too much of a simplification but it'll do. So in old cars, carboned cylanders would have little embers that stayed alight - causing pre-ignition... fuel addtives were to wash those away and get fix the pre-ignition problem.

In a high compression engine you can heat the gas so much as you preasurize it - as the original poster stated - it reaches the flash point too early. Pre-ignition.

-

Lets pause for a moment and thing about how a 4-stroke works. As simply worded as possible.

1- Intake
The piston is travelling down, the intake valve opens and fuel/air enter the chamber. The exhaust valve is closed, so as the piston travels down the preasure drops. It is also being cooled by the cooler air coming in. Low peasure and low tempature. (See why an cold air intake matters? The lower the temp the lower the preasure at this stage... more fuel/air mix put in. Also note that it will raise the temp of the compressed gas later so might require higher octanes)

2- Compression
The intake valve has now closed. The piston travels up compressing the fuel/air mixture. Preasure goes up, so tempature has to.

3- Power stroke.
Some point before the piston reached the top of the compression stroke the spark plug fired. It takes a split second for that flame reaction to really kick in, but on the other hand, a high revving engine would also take a split second to start the downward stroke... timing is where we set the time the spark occures. We want it to spark just in time to get a full power stroke, but not too early as to fight against the piston travelling up in the compression stroke.

4- The piston reaches the bottom of the power stroke filled with waste gas and some unburned fuel. Can't be helped. The exhaust valve opens and the piston travels up pushing the waste out the exhaust.

--

Why all that ramble - as the previous poster pointed out - it's all about the timing between compression and power stroke - the instant where the piston stops travelling up (creating preasure) and starts travelling down (creating power). If it ignites too soon some of the power is wasted fighting against the compression upstroke. Using too low an octane, carbon build-up, the wrong timing etc can lead to pre-ignition. Pre-ignition is the engine fighting with itself and not working efficiently.

However, the counter balance as the original poster pointed out is that - high octane fuel has less energy. Using too high an octane fuel won't hurt the bike, like preignition would, but it will rob you of money, power, and fuel milage. Not much, but it does.

The trick is to use lowest fuel octane you can use in the vehicle and NOT have preignition. Honda as stated, knows what they are talking about so use what ever it says in the manual.

added background, but the O.P. had it down.
woot.

Will this topic ever die? Nope... even if stickied people won't find it :(

So what are you guys trying to say....lol....j/k

OW MY BRAIN HURTS NOW LOL

Short answer?

It's cheapest to run the lowest octane that doesn't pre-ignite.

Honda knew what they were doing, just do what they said.

If you need higher octane than specified by Honda, due to preignition, then you should find out why. Maybe it is simply the modifications to the bike that affect the tempature of the cylanders, and/or carb deposists.

IF that doesn't work for you then use higher octane - but please don't tell me anymore that I need to run higher octane. :p

Im pretty surprised, no one here wants to object or put up an educated arguement?

There is no logical argument -- peeps have been trained by the oil companies for years that higher octane = better performance. And if super costs about 5 cents a gallon more to make and they charge 20 cents at the pump you can see why.

Generally the super contains extra detergents -- so if you get carbon buildup on your piston crown from incomplete burn then hopefully the detergents will clean it up:)

just a quick question regarding octane for 06' 1krr.

Here in Australia it is stated in the honda manual and on the sticker on the tank to run a minimuim of 95 octane!
I think in the US it is 91 octane?

My question is,

IF the only reason for higher octane is, so you can run more advanced timing without detination(thus making more power)? Then would this mean that the Australian Model is running more advanced comparied to US? If this is true? Would this mean that the Australian model is actually more powerful? If it is not? than why would Australians have to run 95 as to 91 in US?

I dont fully understand thats why I am hoping others could explain... Thanks

Sorry dude but I don't think that's the case. There are at least three major ways to measure octane for the pump and depending on where you live in the world determines what formula they post on the pumps. In the U.S. we use the R+M/2. You guys may use the RON only -- you'd have to check the sticker on the pump to see. There is no way I know of to compare them unless they are using the same formula for the rating.

Here's an article that I've posted here before that explains it in non-engineering terms. I thinks it's an excellent read if you like that sort of stuff. Of course my 14 year old man-child tells me I'm a geek:eek:

[quote]The octane number assigned to a motor fuel has very little to do with the actual chemical "octanes" in the fuel and everything to do with how well the fuel resists detonation (which is directly related to the amount of energy (heat) required to get the fuel burning in the first place).

Therefore, it is possible to assign octane VALUES to fuel which contain no octanes whatsoever.


WHY DO WE CARE ABOUT OCTANE? WHAT IS PREIGNITION? WHAT IS DETONATION?
The octane value of a fuel is an empirical measure of its ability to resist detonation and, to a limited extent, preignition. Technically, octane ratings measure a fuel's ability to resist the spontaneous ignition of unburnt end-gases under controlled test conditions.

What is preignition?

Preignition occurs when the fuel/air mixture in a cylinder ignites before the spark plug fires.
It can be caused by burning contaminates (such as carbon, or a spark plug of the wrong heat range) in the cylinder or by extreme overheating.

What is detonation?

Detonation occurs when the flame-front in a cylinder does not proceed smoothly from the point of ignition (the spark plug) to the opposite side of the cylinder.
It refers to the spontaneous ignition of the entire charge in the cylinder. This ignition is often caused by the extreme pressure rise in the cylinder that occurs when the charge is first ignited (by the spark plug).



WHAT ABOUT FUELS?
There are six things to consider when comparing hydrocarbon fuels:

1. Volatility. In short, what's the fuel's propensity to vaporize. This effects the ability to easily mix the fuel with air and the fuel's tendency to vapor-lock. It also determines the pollution characteristics of the fuel where evaporative pollution is a concern.
2. Pre-ignition & knock resistance. Referred to as "Octane value." How much energy does it take to get the fuel burning - how much does it resist auto-ignition from compressive heat? Also, what is the rate of burn of the fuel (which affects the rate of pressure rise)?
3. Energy content. How much energy can be extracted from the fuel as a percentage of its volume or mass.
4. Heat of evaporation.
5. Chemical stability, neutrality, and cleanliness. What additives does the fuel contain to retard gum formation? Prevent icing? Prevent corrosion? Reduce deposits?
6. Safety
The first three factors are often confused and interrelated when, in fact, they measure three completely separate things. There is no natural collelation between them.

General rules:

Heavy fuels (diesel, jet): Low volatility, low knock resistance, high energy per volume
Light fuels (gasoline): High volatility, high knock resistance, low energy per volume

Note that gasoline, partially, makes up for its (relatively) low energy-per gallon by the fact that a gallon of gasoline weighs less (by about 15%) than a gallon of jet fuel.

Octane rating is in no way correlated with engine power or efficiency. There is more potential energy in a gallon of diesel fuel than a gallon of gasoline, yet the diesel fuel has a much lower octane value (more on that below).


HOW DO YOU DETERMINE OCTANE?
Ok, then, how is octane rating determined? First, you go out and get a suitable supply of the fuel which you wish to test. Then,

damn stretch, i got to "The octane number..." then i scrolled down, picking up my jaw off the floor, i am trying to type this post. but thanks for the post slipper...undoubtably, you will get someone who thinks you are wrong, and thinks we all NEED to run atleast 91. my bike actually runs better on 87 than higher octanes. so no argument here.

There will be someone in here that wants to argue. i have argued in 2 different threads about how you should run what they recomend. Everyone else seems to think its a matter of being cheap or something. I think its funny really. There are alot of people on this forum that "think they know, but they have no idea."

HAHA;)

ORIGINAL: DThompson

There will be someone in here that wants to argue. i have argued in 2 different threads about how you should run what they recomend. Everyone else seems to think its a matter of being cheap or something. I think its funny really. There are alot of people on this forum that "think they know, but they have no idea."

HAHA;)


come on dthompson, you know everyone here is an expert, and there isnt possibly anything you could tell them that isnt either wrong or they already know. sometimes i wonder why people even ask questions if they wont accept an answer. like the n00bs who want to get a 1000rr as a first bike.

ORIGINAL: DrDRFT

just a quick question regarding octane for 06' 1krr.

Here in Australia it is stated in the honda manual and on the sticker on the tank to run a minimuim of 95 octane!
I think in the US it is 91 octane?

My question is,

IF the only reason for higher octane is, so you can run more advanced timing without detination(thus making more power)? Then would this mean that the Australian Model is running more advanced comparied to US? If this is true? Would this mean that the Australian model is actually more powerful? If it is not? than why would Australians have to run 95 as to 91 in US?

I dont fully understand thats why I am hoping others could explain... Thanks




Your bike is more powerful. U.S. spec bikes are retarded (timing)

x

Where did you get the info that the US bikes are Retarded in timing as compared to the Australian version? I really want to find out bout this as I have done a few dyno runs and people are all saying that it is not possible for me to get those numbers??? But they are comparing to US model bikes. This is why I think that the two versions are running different maps and are producing different horsepower???

Ya, you better have reputable sources for that bombshell. I've found absolutely zero evidence that U.S. 1kRRs are tuned differently from other countries.

I've been running 87 octane in my '06 1KRR for about two tanks with absolutely no new noises or decreases in performance. I, like many others in this forum, have been trying to spread education to folks who believe that super is better including a link to a website that explains it and includes a dyno sheet showing that lower octane made better, more even power on their particular bike, but no one listens and instead decides to argue because surely they must know better. I'm thinking about doing a couple of dyno runs when I get up some money and compare 87 octane, 93 octane, and race gas (maybe 98 octane?) To get a difinitive answer for all the neysayers out there. I hate it when they ney-say...they're always ney-saying ;)

I don't have any evidence that bikes are tuned differently in different countries. But I just came back from the UK where their minimum octane is 95, and goes up to 103 I believe? Now it may be just a different method of calculation. But there are variations of different motors, at least as far as Honda K-series are concerned that require the higher octane that I am under the impression, US soil does not permit. i.e. K20a2 versus K20a which is only a ~20bhp difference, which can be attributed to .5 more compression and advanced timing in the ECU. If someone knows differently, please speak up, but the circumstantial evidence suggests that there are different honda motors for different lands...

I am under the impression/belief at this point that US fuel is lower octane, hence they can not handle some of the higher andvanced timings that some motors are tuned for. I could very well be wrong, but haven't heard definitive proof either way at this point.

sorry to double post but I forgot my original question...

Say you put a power commander in tuned the maps for advanced timings to take advantage of a higher octane.

Is this something you could get power out of? Is it not true that you can tune for a higher octane without any major hardware changes?

We have a ECU flash for the 02-05 Civic Si which changes the requirements for 86 to 91 octane... Is this not an instance where higher octane should be used? So what everyone is saying is "There is no benefit to using higher octane when your hardware says otherwise"

Just advancing the timing with no engine modifications won't really net you anything except marginal power gains and a lot of extra heat and wear on the engine. I don't know what a K20a2 or K20a is exactly -- is it a bike engine? Bumping the compression .5 doesn't seem like 20hp but I guess it could be done.

the K-series motors, k20a2 k20a3 k20a etc... are the newest honda 4 cylinder auto motor series... the JDM motor is the K20a with slightly higher compression (not sure exactly off the top of my head the exact #s), cam profiles etc... some other things... they're ~20bhp more powerful, but also I assume advanced for higher octane gas.

that answers my question, advancing the timing for higher octane won't do much.

ORIGINAL: Ocelaris

the K-series motors, k20a2 k20a3 k20a etc... are the newest Honda 4 cylinder auto motor series... the JDM motor is the K20a with slightly higher compression (not sure exactly off the top of my head the exact #s), cam profiles etc... some other things... they're ~20bhp more powerful, but also I assume advanced for higher octane gas.

that answers my question, advancing the timing for higher octane won't do much.

But if that was the case then why do people run advance timing and run race fuel? if it didn't make more power they are better of running cheaper fuel?I too thought that maybe in Australia we are running a different map(more advanced) due to our lowest fuel being 92octane. And our highest octane fuel from the pump is 100octane... in our Honda manual it states that we should use a minimum octane rating of 95! Now if the US and Australian bike are exactly the same why do we have to run different octane??? I don't know this is why I am asking on this site as it seems there are alot of people in the know here! Only way to learn is to speculate then ask peps in the know!!! my $0.02.....

Generally when you raise compression significantly you tend to take out timing -- not add it in. Otherwise you get detonation. As for race cars ... NASCAR runs 12:1 in a 358 ci V8 -- adding in timing would grenade that bad boy.

I don't know for a fact that Honda isn't running different maps for different countries. The extra compression in a car motor would account for the 20hp -- timing may or may not be another factor.

In the states we use the R+M/2 formula for calculating octane at the pump. How about some of you guys across the pond find out and post how it's measured in your yard. Different formulas for calculating the octane would be a simple enough explanation on why they require higher octane in Oz.

Some of these posts when over my head but from Slipper's original, I learned I have to increase my Omega 3 fatty acids. Kidding aside, I went to "regular" (washington state gas) from my 3rd tank on and havnt found a reason to go back, not even to the "mid" grade. ps Im a street rider only.

Good thread guys. Just a heads up though. I have a 2004 CBR 600RR and in the manual it states 86 octane or higher is the recommended for this bike. With that said if you look in the owner's manual, we should be changing gears every 7miles our so until we get into 6th gear, so basically about 30miles an hour or so in 6th gear is recommended. With that kind of riding, yeah I guess 86 or higher octane is perfect for that application. But who the hell rides like that? If your riding hard like the average joe, than a higher octane gas is recommended in my opinion. Another heads up for you guys and gals. The other day I looked under my back seat, and noticed a sticker with info for my bike. You know info like spark gap size, tire info, and oh yeah octane recommendation. CHECK THIS OUT.... Honda recommends 91 octane for my bike afterall. No sh*t. Check your sticker and let me know if yours has the same thing. I bought my bike in Canada, but that shouldn't make a difference. Ever since I noticed the sticker, I've switched to 91 octane. Bike runs the same as it was with 87 octane to tell you the truth. But I just wanted to go with what the sticker seat said. I just picked the higher number, to make sure because in 2nd gear I'm doing over a hundred, so I just don't feel right using 87. Why would there be a discreptancy from what is stated in the manual and what is stated under the back seat on a sticker? Okay guys you know the drill, go to your back seat and read the sticker, do you see 91 on there? Let me know, and let the forum know this as well. I'd hate to see someone screw up there bike, because they were running 87 when really we should be riding 91 minimum. Just my 2 canadian cents. And no I'm not trying to argue or go against other opinions on here, just reading you the facts, thats all.

ORIGINAL: HondaCBR600RRhunk

Good thread guys. Just a heads up though. I have a 2004 CBR 600RR and in the manual it states 86 octane or higher is the recommended for this bike. With that said if you look in the owner's manual, we should be changing gears every 7miles our so until we get into 6th gear, so basically about 30miles an hour or so in 6th gear is recommended. With that kind of riding, yeah I guess 86 or higher octane is perfect for that application. But who the hell rides like that? If your riding hard like the average joe, than a higher octane gas is recommended in my opinion. Another heads up for you guys and gals. The other day I looked under my back seat, and noticed a sticker with info for my bike. You know info like spark gap size, tire info, and oh yeah octane recommendation. CHECK THIS OUT.... Honda recommends 91 octane for my bike afterall. No sh*t. Check your sticker and let me know if yours has the same thing. I bought my bike in Canada, but that shouldn't make a difference. Ever since I noticed the sticker, I've switched to 91 octane. Bike runs the same as it was with 87 octane to tell you the truth. But I just wanted to go with what the sticker seat said. I just picked the higher number, to make sure because in 2nd gear I'm doing over a hundred, so I just don't feel right using 87. Why would there be a discreptancy from what is stated in the manual and what is stated under the back seat on a sticker? Okay guys you know the drill, go to your back seat and read the sticker, do you see 91 on there? Let me know, and let the forum know this as well. I'd hate to see someone screw up there bike, because they were running 87 when really we should be riding 91 minimum. Just my 2 canadian cents. And no I'm not trying to argue or go against other opinions on here, just reading you the facts, thats all.
Your "facts" are wrong. You are misinterpreting the sticker on your bike. The sticker and the manual are actually saying the same thing. Read this (http://cbrworld.net/forums/thread/50053.aspx) (I just don't feel like re-typing it)

I read it again and the numbers don't change by starring at it, believe me. The manual says 86 or higher octane and the sticker under the seat says 91. Anybody else read the same thing, post on here.

well...if you take what abad's thread says and apply it to the numbers...makes perfect sense...but alas, use what you want to make your heart feel good and your head good!

i now only use super duper thug gansta mawfaki octane gasoline that can only be found in the hoods of LA...it's rated like 1000 octane or something...and it really does make my bike go faster!!! why? cause everytime i gas up with this stuff, i get mugged, so in addition to the price of gansta octane gas...which is bling...and the amount of money they take from me...my wallet is so light that just the weight savings alone made my bike go faster! i have tried the same thing at other places, but the thugs there don't take just the right amount of money so power suffers.

Yeah yeah boyeeeeeeeeeeeee!!!! Thats what I'm talkin about. My homey your the only one that makes sense around here.:D

[quote]ORIGINAL: abadfish


Maybe if you retype what it is you meant to say, than people would actually be able to understand you.

This post has been moved to : Octane discreptance, a must read. Do a search, everyone has bailed ship to that post which I started. Maybe then you will understand what I meant. see you there.

The dealer I bought my bike from recommended 91 (are they in bed with the oil companies?). I am considering going down a grade, but I read somewhere about unplugging your battery when you change octane to "re-set" the bike. Any validity to this?

Sounds like hog wash to me, about resetting with the battery and sh*t. Go to the other post I mentioned above, its causing a lot of controversy, what fun!!!

Dthomspon:
There will be someone in here that wants to argue. i have argued in 2 different threads about how you should run what they recomend. Everyone else seems to think its a matter of being cheap or something. I think its funny really. There are alot of people on this forum that "think they know, but they have no idea."

HAHA

I always run 93 octane in my bike no matter what anyone on here says. Always worked for me.


Seems like you should be arguing this one DThompson, wait, are you for or against it??

bushmaster -- what you trying to do ... stir the pot?

Eventually I'll change my tune and go along with the '93 is best no matter what anybody says' mentality. I figure with all the peeps buying the 93 then my 87 will be much cheaper:D

No, just thought his posts were funny,

ok i am stll a little confused should i run 91-or 87 on my 061krr?i have only ran 91 or better beacuse that is what the dealer told me. i had a turbo car a while back that need 91 but it was turboed. i read this post and still very confused [sm=smiley29.gif]

Read the manual. Your dealer may not be as informed as he purports to be. But then again, he may know something about the gas in your local area.....

check with your manual...it'll tell you exactly what you need to run, but make sure you are not confusing RON for PON, etc.

mkhaynesaz, im not sure about a 1000RR. If im not mistaken they actually do require 91 octane. Check your owners manual.

Woohoo, good post. Should be required reading for every shade tree mechanic. Explains everything about normal fuels. BTW Race fuels have the higher octane of gas, but lower volatility of jet fuel and diesel. SO they burn faster and with more ummph, but are still safe to use without fear of detonation(knock).

I understand the argument...or a better word...reason...to use low octane fuel.

I also understand how an engine works...haven't repaired or rebuilt every single one made...but have some and understand...

Intake..the piston in a given cylinder is traveling down...creating a vaccum...thus INTAKING...the fuel...

Compression...piston is beginning to travel up...making the cylinder area smaller and smaller as the piston rises...and gets closer to both
the intake valves and the spark plug, which ignites the gas molecules, tiny droplets of both fuel and air, aka atomized mixture.
This gets all that wonderful gasoline and air mixture, which is what explodes/burns and forces the piston to turn the crankshaft,
into the most compact and efficient gaseous form possible.

Ignition...this starts just about when the piston is at it's highest point...just before top...dead...center...or TDC.
When the piston is at full TDC...ideally this is when the fuel and air mixture should be at it's most dense, causing the cleanest burn
(controlled explosion) possible.

(Before TDC is how you set the timing for a particular engine...but that's another topic.)

Exhaust...any unspent energy not efficient enough to turn the crank, which turns the sprockets, which drive the chain,
which turns the rear wheel, which propels you forward....wheeeeeeeee....

the waste products from the unburned fuel, fuel is not absolutely pristine and sterile stuff afterall...

...and to dis-allow a build up of so much pressure that the enitre engine would eventually explode...

The Exhaust valve opens...the gases run out the valves...into the headers...down the pipe(s)...and out the exhaust canister.

That is what is known in laymen's terms as Suck...Squeeze...Bang...Blow.

Having said all that....?

My 94 F2 run better on 93 octane fuel...whether it's supposed to or not.

The engine has more power...has less naturally occuring stumble...and makes a lovelier hum on 93.

On 86...it runs like ass.

Go figure.

this topic needs some science...not just blather. I wrote most of this some time ago on another forum...for sleds in particular.

Tahoe mentioned the RON and (R+M)/2 versions of octane number..he's right on. The octane requirement of a straight RON number would be a higher number than an (R+M)/2....so check what the mfr calls for.

Octane is a measure of the energy it takes to ignite a fuel (resistance to detonation is a different perspective, but gets the same point across). It is NOT a measure of the energy in the fuel. Power improvements from utilizing higher octane are a result of improved effeciency in the combustion process. Energy in the cylinder has various forms and comes from the compression of the air/fuel, from the heat in the piston/head/cylinder walls/spark plug and the last energy to throw gas over the hump is from the spark itself. This energy input is necessary to create the downhill chemical process....fuel+O2+energy = water, CO2, and LOTS of energy. When you don't have enough energy to get it over the hump the combustion process is not completed in the intial event.

Ideally the fuel/air mix is ignited by the spark before TDC and the flame front travels out radially from that point....and by the time the process createspressure, the piston is on the way down (we are talking a couple degrees after TDC). This event is obviously VERY fast...but so is the piston speed at 7000rpm.

In lean mixture, the flame front has trouble propagating. In a rich mixture, the extra fuel robs heat from the reaction, or prevents the spark from jumping the gap in the plug.

If you use a higher octane than called for, not all the fuel ignites from the initial energy put into the chamber by the spark (remember the lower octane RON number portion of the fuel)...for the rest ofthe fuelto ignite, it takes the added energy of heat and pressure caused by theflame front to ignite it. This can create other smaller flame fronts in remote area's that impeed progress of the initial front in the worst cases. Regardless, by the time full combustion has happened its too late for it to contribute to the power making process....well, not very efficiently anyway....you are building pressure, but the piston is already moving away.

Higher octane is not running your engine lean in the sense of mixture, but a similar effect on power....a more comparable description would be retarding your timing. You wouldn't change jetting to make the best use of higher octane, you would change your ignition timing or compression. Newer cars with knock sensors do the prior. You bike doesn't have a knock sensor, and the ecu has no data logging or avergaing capbilities...there'sno reseting or whatever.

Ethanol (alcohols) actually has a higher octane rating than gasoline. Many gas station sell 87 octane with 10% ethanol added to sell you89 octane. However, ethanolhas a lower energy content and is hydrophillic (absorbs water). Yeah, thats bad. It creates a lot of difficulties for the gas companies in terms of mixing and transporting. Ethanol mixtures will run lean in carbureted engines...bikes, sleds, weed eaters...you name it. It can be compensated for in jetting.

Compression ratio alone doesn't dictate octane...though they go hand in hand. 2 strokes will always be lower compression than a 4 stroke on the same octane because the cylinder is warmer....it doesn't get a whole pumping cycle to cool off.

Static compression is the number everyone throws around, and is a ratioof the swept cylinder volume to compressed volume. And truely, running compression ratio's are mostly anything but that number....cylinder filling efficiecies are 75-80% at low rpms (and WOT)but theyexceed 100% at high rpms (and Wide Open Throttle)...how is by acc

First of all...excellent post...though some may find it a bit...wordy...

I liked it...

Ethanol (alcohols) actually has a higher octane rating than gasoline. Many gas station sell 87 octane with 10% ethanol added to sell you89 octane. However, ethanolhas a lower energy content and is hydrophillic (absorbs water). Yeah, thats bad. It creates a lot of difficulties for the gas companies in terms of mixing and transporting. Ethanol mixtures will run lean in carbureted engines...

Ethanol ruined the fuel system in my old...220k+ Mits Eclipse.

Also, it costs more to make a gallon of ethanol gas than it is sold for...so yes...politics.

Where do you get this U4 race gas...and what jetting kit are we talking?

ORIGINAL: chainstretcher


Generally the super contains extra detergents -- so if you get carbon buildup on your piston crown from incomplete burn then hopefully the detergents will clean it up:)




If you're worried about getting carbon deposits, keep with the lower octane fuels and by a 4 stroke fuel system cleaner. I do this monthly and keeps the engine running nicely. Fill up the tank half way and put it into the tank, then fill the rest of the tank up. Simple.

Can get it from Hein Gericke and probably other places too.

now why would a car designed to run on 87 require higher octane?

it's possible that due to age, there is enough build up of carbon deposits, etc. within the cylinders to increase operating temps dramatically, pressure, etc. lower octane fuels in this environment would combust even before TDC due to the high operating temps...so you stick in higher octane and it makes the engine run much better.

i'm not saying this is what is up with BMG's bike, but just some possible answers.

anyone remember dad's old a$$ olds or buick that always pinged and ran like crap...and if you turned off the engine, crazy car would still sit there idling for a bit?

put high octane in there and it ran great...and we stood around and said...WTF? hahahahahhah

ORIGINAL: Tahoe SC

now why would a car designed to run on 87 require higher octane?

it's possible that due to age, there is enough build up of carbon deposits, etc. within the cylinders to increase operating temps dramatically, pressure, etc. lower octane fuels in this environment would combust even before TDC due to the high operating temps...so you stick in higher octane and it makes the engine run much better.

i'm not saying this is what is up with BMG's bike, but just some possible answers.

anyone remember dad's old a$$ olds or buick that always pinged and ran like crap...and if you turned off the engine, crazy car would still sit there idling for a bit?

put high octane in there and it ran great...and we stood around and said...WTF? hahahahahhah


Naaa...I've given my bike a compression test...ridden it hard by opening up the throttle...high rpm's
and then letting off and blipping the throttle, or downshifting...and it's smooth as silk.

Just runs better on 93 octane.

Also runs best on Chevron gas as opposed to say Shell or a local Mobile station.

Part of it may be my imagination...part of it may be the gas...and part of it may be the never ending debate over this topic.

I've read it both ways...

A low octane fuel may burn all at once (detonate) or even be
ignited by hot spots or carbon chunks in the cylender and ignite too early.
Preignition and detonation cause severe wear and damage to the lower end of
the engine such as pistons, con rods and bearings. The high octane fuel
burns slowly and evenly and should be finished by the time the valve opens.
The higher octane also has a higher combustion temp. than the low octane and
will not preignite.
On the other hand, using too high of an octane can burn valves. Because
of the slower burning properties of high octane fuels, the low octane
engines will open the exhaust valve before the fuel/air mixture has finished
burning and will elevate the valve and exhaust manifold temps causing
premature valve wear or failiure and may burn holes in the exhaust.
So, the best thing to do is use the octane rating in the owner's manual

That guy says the exact opposite seems like...

Then this guy...


There have been a lot of ideas thrown out there about this, so here's
another one.
Think of higher octane gasoline as a slower burning fuel. All things
being equal, it takes longer to ignite and longer to burn. Thus, high
octane fuel is desireable in situations where the tendency to knock
is high, such as high compression ratios and forced induction. In
essence (no pun intended), higher octane fuel needs more ambient heat
in order to start the reaction.
In order to make use of the higher octane fuel in an engine which is
designed for low octane fuel (while keeping the same spark plugs),
one must advance the timing--so that the spark plug fires a little
prematurely. In this configuration, higher octane fuel will generally
make a low octane engine feel smoother.
However with everything setup stock, you will gain nothing from
higher octane fuel. If you hear pinging and you cannot eliminate it,
then you should try a slightly higher octane--but only enough to
eliminate it.

Then this from wikipedia
[quote]
Effects of octane rating Higher octane ratings correlate to higher activation energies (http://en.wikipedia.org/wiki/Activation_energy). Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression rati

It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

I say...run whatever works best for your bike...in your particular climate...etc.

I'm in agreement with the Wikipedia definition. Activation energy is perfect wording.

If your bike runs better on higher octane than called forit could be either the carbon build up issues, or your jetting.....remember, a high octane has an effect of leaning out the mixture....those fuel molecules with high "activation energy" don't combust in the initial event and hence use none of the oxygen.