Octane Ratings: higher = better performance, right?


grayracer513

A lot of confusion, mystery, and myth surround the simple question of what grade of fuel to use, what octane ratings mean, what detonation is, and the value of racing fuels. Part of the reason for that is the marketing that oil companies have done for over 70 years, in which they have promoted high octane fuels as an easy avenue to increase performance, when in fact, this is a very much backwards perspective on the matter. It is engines originally built for higher performance that need it.

 

Let’s see if we can clear up some of the misinformation! Click on to page two where we'll start with "Detonation: what is it?"

 

 

octane.jpg

 

 


 

Detonation: what is it?

 

Gasoline engines are designed to burn gasoline. They are not designed to “explode” or detonate it. There’s a huge difference. During normal operation, air and fuel is introduced into the combustion chamber, compressed so as to improve the force of expansion as it burns, then near top dead center, it is ignited by the ignition system. What is supposed to happen is that the fuel immediately adjacent to the spark plug is ignited, and as it burns it ignites the fuel surrounding it and so on outward from there very much like a wave of flame. It’s like making a circle of match heads on top of a table and dropping a lit match in the middle (or anywhere else in the circle). The flame will spread rapidly, but never instantly.

 

Detonation is different. Detonation is the simultaneous ignition of all of the unburned fuel in the cylinder at the time it occurs, all at once. Normal ignition is a heavy, sudden push that continues over 90 or more degrees of crank rotation; detonation is like hitting the piston with a hammer instead of pushing it, and often has the effect you would expect from doing that kind of thing.

 

Up next: Why and how does detonation happen?

 


 

Why and how does detonation happen?

 

Detonation occurs when the heat and pressure in the cylinder rise to the point where the gasoline is ignited by just that, and not by contact with a flame. Once that level of heat is reached, it affects all of the fuel that remains to be burned equally and at the same time, rather than progressively, as a flame traveling from droplet to droplet of the fuel mist, and all of it ignites in the same instant, creating insanely high spikes of pressure that can and do cause horrendous damage.

 

In practice, the causes are one or more of excessive heat in the combustion chamber that allows temperatures to rise too high during compression, timing that is too far advanced, allowing the flame to build too much pressure before it can effectively turn the crank, hot spots in carbon deposits that ignite the fuel early, or simply a fuel the does not have sufficient resistance to being ignited by heat and pressure alone. That is, a fuel with an insufficient octane number.

 

Most of the time, what happens is that ignition takes place normally, and the flame front begins to spread over the combustion chamber as intended. But, as the flame spreads, heat and pressures in the chamber rise until they reach the point where the fuel can no longer tolerate them, the remaining fuel from the previous intake cycle detonates, often resulting in an audible “ping”. It can produce a sound reminiscent of having filled the top end with marbles or something, and can be quite destructive if it happens early enough in the power stroke. The correction, assuming that the engine is timed and jetted appropriately is to increase the resistance of the gasoline to being ignited by sources other than open flame. That means, a fuel with a high enough octane number.

 

That’s the form detonation usually takes, and at that level, in which only a part of the whole fuel charge is detonated instead of burned, it isn’t nearly as harmful as it can get. In the extreme, where the gasoline is pre-ignited, that is, ignited earlier than intended by an overheated engine, glowing carbon, etc., a larger percentage, or even all of the fuel may be detonated at once, and the results can be catastrophic.

 

Up next: What are the factors that influence normal combustion?

 


 

What are the factors that influence normal combustion?

 

Compression, ignition advance, and the fuel’s tolerance of them. Compression is simple to understand. Compression creates heat, and more compression creates more heat. Possibly too much more.

 

Ignition timing is a little more complicated, but still pretty easy to understand. In a piston engine, there is a mechanical “sweet zone” in the rotation of the crankshaft that goes from just after top dead center (TDC) to around 90 degrees after top dead center (ATDC). In this zone pressure on top of the piston does the most efficient job of turning the crank. It’s also important here to note that throughout this zone of rotation, the combustion chamber volume is constantly expanding. Gasoline of any kind or blend burns at nearly the same rate under pressure regardless of the situation.

 

Now, picture the piston having just past TDC and starting down the bore. If you light the fuel now, it will take a certain amount of time for it to develop a significant amount of pressure to really do anything about pushing the piston down. While it’s trying to build pressure, the piston is moving away from it at the same time, and little is gained. So the timing is set to ignite the fuel in advance of TDC. This allows the burning fuel to build up a meaningful amount of “push” by the time the piston starts down, and ideally burning most of it within the “sweet zone”. Since the engine will speed up, but the fuel burn won’t, the faster the engine spins, the more advance it needs as it picks up speed.

 

But if the fuel is ignited too early, the pressure and heat may reach critical levels before the combustion chamber volume has begun to enlarge adequately, and the portion of the fuel that lies in front of the advancing flame may then detonate.

 

Octane is the fuel’s detonation resistance.

 

And that’s all it is. Gasoline is a blend of several hydrocarbon solvents, among them toluene, benzene, heptane, and octane, plus a number of less active ingredients designed to do things other than add to the fuel’s energy levels. The number “100 octane” is based on the detonation resistance of 100% iso-octane. When a fuel is labeled “95 octane”, it resists detonation under pressure as well as a blend of gas consisting simply of 5% n-heptane and 95% iso-octane.

 

Octane number indicates ONLY this resistance to detonation. High octane gas does not burn hotter, colder, easier, harder, cleaner, dirtier, or with any more or less power because of the octane number. Differences such as any of these other fuel characteristics that actually do occur are the result of the overall fuel blend used for that particular gasoline, and it is both possible and common to find major differences in these qualities in different gasolines that all have the same octane rating. Race gas is a perfect example of this, as we will see later.

 

Up next: Why can I use 91 octane when my manual says I need at least 95?

 


 

Why can I use 91 octane when my manual says I need at least 95?

 

There are three different rating systems used to find the octane number of a fuel. The oldest is the Research Method. This method uses a special test engine with a variable compression ratio to compare the relative detonation resistance of fuels with equivalent heptane/octane mixes.

 

A newer method called the Motor Octane method also uses a test engine, but runs at 900 RPM instead of 600 as in the Research Method, and uses higher temperatures and variable timing to compare fuels. It is considered a more accurate gauge of how gasoline will perform in modern engines than is the Research Method, but it’s rarely used in any kind of advertising because the rating numbers tend to run from about 8 to 12 points lower than the ratings arrived at with the Research engine. A fuel rated 100 Research Octane Number (RON) will only post up a best of 90-92 Motor Octane Number (MON), in spite of the fact that they have very close to the same real detonation resistance regardless of the test method. But oil companies are much more likely to promote their products by quoting RON than MON, if you let them, because it comports with all those marketing myths they’ve been selling all these years. This is where the third rating method comes in.

 

In an effort to reduce consumer confusion and promote some level of consistency, the US Government requires that the average octane number achieved by both methods be posted on gas pumps and be called the “Anti-Knock Index”. You see it as “R+M/2” on the pump. So when your manual says you need 95 octane, and your bike is from Europe or Japan, you’re being quoted Research Octane Number. The equivalent Motor Octane number would be about 86, and the average would be 90-91, so that’s what you would look for at the gas pump.

 

Up Next: So, do I need race fuel?

 


 

So, do I need race fuel?

 

If you can buy pump gasoline that meets the minimum octane requirements of your engine, you don’t need race gas or octane boosters to raise the octane number any higher. Your engine will run detonation-free on any gas that rises to that level, and paying any money out to run the octane rating up any higher than that is just a pure waste.

 

There are, or may be, several other reasons to improve on the pump gas you find in your particular area. A lot of what goes into commercial automotive pump gas is there to do things other than create power, and those ingredients may be partially or completely inert as far as their contribution to the amount of power the engine can produce from it (referred to as “energy content”). Ethanol fuels are a good example. By itself, ethanol has an RON of 108, but its MON is only 88. E85 fuel is 104 RON, and only 85 MON. Furthermore, to get the same power as non ethanol gasoline, you have to burn 15-25% more of it.

 

Oxygenating agents are added to pump fuels to aid in the more complete burning of fuel for the purpose of reducing emissions. Oxygenates are added to race fuels as accelerants, and there is often a fairly big difference in the chemicals chosen for that job. Ethanol is an oxygenate, but it produces much less energy per volume in and of itself than most gasoline components, so it reduces the energy content. MTBE (methyl tertiary butyl ether) is an oxygenate that produces more energy when burned than ethanol, and releases more oxygen in the process, so it’s more often used in race fuels.

 

You can generally gain power through using race gas, but rather than a gift that keeps on giving, it’s a modification that you have to keep on paying for for as long as you want to use it, and it often requires rejetting to make the switch, so you kind of have to stay with it. The extra power IS NOT a result of the usually higher octane number, but comes from the specific blend of hydrocarbon compounds used in the formula. A number of octane increasing components such as xylene and toluene also increase the energy content since they actively contribute to the combustion event, as opposed to tetraethyl lead, with is essentially inert as a fuel component.

 

As far as vaporization rates, burn rates, etc., etc., differently configured engines require fuels with different attributes. Factors are carbs vs. fuel injection, long vs. short intake tracts, high vs. low RPM operation, and steady state vs. non-steady state operation (like boats and airplanes vs. dirt bikes). Race fuels come in such diverse varieties for this reason.

 

Incidentally, octane boosters are mostly snake oil. There are a few good ones that are available from automotive speed shops, but most of the ones you see on the shelf at the auto parts store are useless. They say they raise octane by one or two or three points, but that’s a change of 0.1 to 0.3, not 1 to 3 octane. Injector cleaner might actually be more effective.

 

Next: So, will more octane benefit me?

 


 

So, will more octane benefit me?

 

An excess of octane number beyond what your engine needs is completely harmless and has no downside except for the damage it does to your wallet. If it’s simply a question of octane, as long as you don’t ping on ordinary pump premium, you don’t need any more octane to prevent detonation, and preventing detonation is the only thing high octane is good for.

 

Have a question or comment? Post it below! You'll be helping to expand the depth & value of this topic and at the end of the day, that's my goal! :thumbsup:

Edited by grayracer513

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Klotz octane booster is both snake oil and octane increment.

 

Klotz Octane booster smells awesome, increases octane, runs cooler, runs cleaner, promotes longer life, cures cancer, and adds super powers to my 450.

 

For $55 a gal, how can you go wrong?

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I recommend nuking the original article and replacing it with this one.

Thanks!

 

Someone mentioned that I am nitpicking about the terminology, but I am just trying to make it clearer. I have spent the last 14yrs working for NGK Spark Plugs and deal with these things everyday.  If the purpose of these articles is to educate, then we should provide correct concepts and terminology. 

 

Also, to address Slartidbartfast's comment about "pre-ignition by itself means nothing" - not exactly sure what you mean, but that doesn't sound right to me.  Knock and pre-ignition are two different phenomenon.  Severe knock can raise the cylinder temperature enough to heat up components, in turn causing pre-ignition.  But pre-ignition can also occur without knock. For example, when someone uses a spark plug with too hot of heat range. The ceramic on the firing end overheats when heat cannot dissipate to the cylinder head fast enough.  The hot ceramic will turn into the source of ignition - before the spark occurs. Furthermore, if there is no knock, you usually don't hear any noise during pre-ignition.  The cylinder pressure and temperature rise so fast that it only takes a few seconds of pre-ignition to melt a plug or piston.  On the other hand, I have heard engines run all day long, full load, max rpm, with heavy knock and they survive without failing, because pre-ignition does not occur. So - knock and pre-ignition are related, but are two distinct forms of abnormal combustion.  And they can occur independently.

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FWIW:  This was taken off the VP Fuel website.

 

The four most important properties of racing fuel

 

You can't make a racing fuel that has the best of everything, but you can produce one that will give your particular engine the most power.  This is why we produce different fuels for different applications.  The key to getting the best racing gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine.

1.        OCTANE – This is simply the rating of a fuel’s ability to resist detonation and/or preignition.  Octane is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON), and Pump Octane Numbers (R+M/2).  Pump Octane Numbers are what you see on the yellow decal at the gas stations and represents an average of RON and MON.  VP reports MON ratings because this method tests a fuel’s performance under a heavier load than the RON method, thus better simulates racing conditions. Most other companies use RON because it sounds better in marketing messages. Don't be fooled by high RON numbers or an average—MON is the most relevant for a racing application.  However, a fuel’s ability to resist preignition is more than just a function of octane.

 

2.        BURNING SPEED - The speed at which fuel releases its energy.  In a high-speed internal combustion engine, there is very little time (real time - not crank rotation) for the fuel to release its energy.  Peak cylinder pressure should occur around 20° ATDC.  If the fuel is still burning after this, it is not contributing to peak cylinder pressure, which is what the rear wheels see.

3.        ENERGY VALUE - An expression of the potential in the fuel.  The energy value is measured in BTUs per pound, not per gallon. The difference is important.  The air:fuel ratio is in weight, not volume. Remember, this is the potential energy value of the fuel.  This difference will show up at any compression ratio or engine speed.

       4. COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization.  The higher the heat of vaporization, the better its effect on cooling the intake mixture.  This is of some benefit in a four-stroke engine, but can be a big gain in two-stroke engines.

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Av Gas , due to the aromatics, iso octane and good old Pb/ organics, is what make is wonderful fuel. Planes go high, hence reduced air pressure. Garbage fuel would vapour lock!!! Yes, to make it worth while, advance ignition timing and raise static compression. Even in a 25 hp 2 stroke outboard, there was more power, with no change to tuning. Aromatics have more BTU,s than most things in Gas. 

regards 

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FWIW:  This was taken off the VP Fuel website.

 

 

OCTANE – This is simply the rating of a fuel’s ability to resist detonation and/or preignition...

 

 

...However, a fuel’s ability to resist preignition is more than just a function of octane.

Looks like even the VP guys don't fully understand the difference between knock and pre-ignition...

 

From VP website quote: "This is simply the rating of a fuel’s ability to resist detonation and/or preignition." It's not detonation or pre-ignition - it's the resistance to knock.  Pre-ignition is also known as surface ignition - where a hot spot ignites the air-fuel mixture before the spark between the spark plug gap does. When we do pre-ignition (spark plug heat range) testing, we are always limited by knock when using lower octane fuels. In other words, knock occurs first when advancing the ignition timing to find the pre-ignition threshold. If we use high octane fuel (ex. 103 RON), then we can usually avoid knock and heat the spark plug up enough to cause pre-ignition by advancing the timing.

 

Another quote from VP website: "However, a fuel’s ability to resist preignition is more than just a function of octane." It's not the ability to resist pre-ignition - it's the ability to resist knock. Low octane fuel doesn't directly cause pre-ignition. Knock occurs first if the spark plug heat range is appropriate.  Severe, high levels of knock can eventually overheat combustion chamber components enough to cause pre-ignition (surface ignition) - but the knock comes first.

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To prevent destructive knock or ping you would dither ignition timing based on load, temperature, and octane like modern automotive engines do. Automotive ECMs can also indirectly adjust the effective compression ratio by adding inert exhaust gas with external valves (EGR) or by playing with valve timing.

I don't know about modern injected bikes but dinosaurs like my XRs don't have any of that stuff so I use the highest octane fuel I can get. 

Not because of some illusion of greater power but simply because you just cannot hear spark knock or pinging on an air cooled bike with a pipe.

It's worth the 20 cents a gallon for the peace of mind that my piston will never look like some midget has been hammering on it with a welding hammer

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On 12/29/2016 at 5:11 AM, danoliveira said:

Let me point something out.

"Detonation occurs when the heat and pressure in the cylinder rise to the point where the gasoline is ignited by just that, and not by contact with a flame". - Did you mean spark?

"
as a flame traveling from molecule to molecule" - that is far from how physics works.

 

No, I meant flame.  The gasoline in the combustion chamber does not collect itself into a single contiguous blob.  The air/fuel mix is a mass of air with separate droplets of gasoline suspended in it.  The spark plug ignites only the gasoline droplet(s) that lie immediately adjacent to the plug, and from there, each burning droplet ignites its neighbor, and so on. 

Using the phrase, "molecule to molecule" may have been chemically incorrect, but if you understood from that that the flame proceeds as an expanding wave rather than a single instantaneous event, the phrase served it intended purpose correctly.

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On 1/22/2017 at 0:37 PM, v-rider said:

Looks like even the VP guys don't fully understand the difference between knock and pre-ignition...

 

From VP website quote: "This is simply the rating of a fuel’s ability to resist detonation and/or preignition." It's not detonation or pre-ignition - it's the resistance to knock.  Pre-ignition is also known as surface ignition - where a hot spot ignites the air-fuel mixture before the spark between the spark plug gap does. When we do pre-ignition (spark plug heat range) testing, we are always limited by knock when using lower octane fuels. In other words, knock occurs first when advancing the ignition timing to find the pre-ignition threshold. If we use high octane fuel (ex. 103 RON), then we can usually avoid knock and heat the spark plug up enough to cause pre-ignition by advancing the timing.

 

Another quote from VP website: "However, a fuel’s ability to resist preignition is more than just a function of octane." It's not the ability to resist pre-ignition - it's the ability to resist knock. Low octane fuel doesn't directly cause pre-ignition. Knock occurs first if the spark plug heat range is appropriate.  Severe, high levels of knock can eventually overheat combustion chamber components enough to cause pre-ignition (surface ignition) - but the knock comes first.

Pre-ignition can be caused by insufficient octane number.  It's a fairly rare occurrence because in order for this to happen, the heat generated by compression has to rise to the point of igniting the fuel before anything else does it, in the manner of a Diesel engine, and the octane number has to be very far off to accomplish that.  "Anything else" might include carbon deposits glowing from compressive heating, or another indirect source of ignition from leftover or accumulated heat that happens prior to the intended ignition point.  Pre-ignition essentially produces detonation by moving the effective ignition timing to a point that is too early.

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On 12/29/2016 at 0:14 PM, mixxer said:

To the extreme lover of self... Dan Oliveria..

(...)

Continue with your self love...

What? I have no idea what's this about self-love.
 

On 2/3/2017 at 1:43 PM, grayracer513 said:

No, I meant flame.  
(...)
Using the phrase, "molecule to molecule" may have been chemically incorrect, but if you understood from that the the flame proceeds as an expanding wave rather than a single instantaneous event, the phrase served it intended purpose correctly.

The flame is started by the spark. I understand that the combustion process can be broken up into phases, but your terminology is confusing to me.
I think that in a technical explanation, one should be expected to be clear and precise...
Maybe your article is good, but some things in it give me pause.
 

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On 12/23/2016 at 8:55 AM, Spooge said:

Great post, thank you.  

 

You did however forget to mention how good race gas exhaust smells, particularly when mixed with two-stroke oil.....  

We used to put some Castrol in a coffee can and heat it on a hot plate in the shop during the winter.   That was our air freshener.

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On 1/19/2017 at 8:08 PM, v-rider said:

Thanks!

 

Someone mentioned that I am nitpicking about the terminology, but I am just trying to make it clearer. I have spent the last 14yrs working for NGK Spark Plugs and deal with these things everyday.  If the purpose of these articles is to educate, then we should provide correct concepts and terminology. 

 

Also, to address Slartidbartfast's comment about "pre-ignition by itself means nothing" - not exactly sure what you mean, but that doesn't sound right to me.  Knock and pre-ignition are two different phenomenon.  Severe knock can raise the cylinder temperature enough to heat up components, in turn causing pre-ignition.  But pre-ignition can also occur without knock. For example, when someone uses a spark plug with too hot of heat range. The ceramic on the firing end overheats when heat cannot dissipate to the cylinder head fast enough.  The hot ceramic will turn into the source of ignition - before the spark occurs. Furthermore, if there is no knock, you usually don't hear any noise during pre-ignition.  The cylinder pressure and temperature rise so fast that it only takes a few seconds of pre-ignition to melt a plug or piston.  On the other hand, I have heard engines run all day long, full load, max rpm, with heavy knock and they survive without failing, because pre-ignition does not occur. So - knock and pre-ignition are related, but are two distinct forms of abnormal combustion.  And they can occur independently.

In other words, reading your spark plug does have some merit?

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9 minutes ago, Jimmy Pascol said:

We used to put some Castrol in a coffee can and heat it on a hot plate in the shop during the winter.   That was our air freshener.

Great idea, I'm gonna start doing that!  Hopefully it will help cover up the dog farts.  :banana:

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Here in Dallas Fort Worth we have only ethanol fuels available. There are TWO locations in outlying areas that sell 91 ethanol free.

Do you feel that one gallon of race fuel (c12) mixed with three gallons of ethanol gas is a safe and okay ratio?

Edited by Texasxcrider

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On 2/3/2017 at 1:52 PM, grayracer513 said:

Pre-ignition can be caused by insufficient octane number.  It's a fairly rare occurrence because in order for this to happen, the heat generated by compression has to rise to the point of igniting the fuel before anything else does it, in the manner of a Diesel engine, and the octane number has to be very far off to accomplish that.  "Anything else" might include carbon deposits glowing from compressive heating, or another indirect source of ignition from leftover or accumulated heat that happens prior to the intended ignition point.  Pre-ignition essentially produces detonation by moving the effective ignition timing to a point that is too early.

I think it would be clearer to put it this way: Low octane fuel can cause knock. (Knock occurs after the spark occurs.) Excessive knock can heat up the combustion chamber components so much that hot spots can eventually cause pre-ignition. (Pre-ignition means that the air-fuel mixture is ignited before the spark occurred at the spark plug gap.) That's the order of how it happens. In the automotive engineering world, we don't use the word detonation to describe anything like knock or pre-ignition. We really don't use the word detonation to describe anything...  

The line is getting blurred a little as there are recent findings that oil mist and carbon in the cylinder can also cause a phenomenon called "Megaknock". (This usually only occurs in turbocharged engines.) Megaknock is similar to pre-ignition in the fact that the cylinder pressure starts to rise quickly from combustion before the spark event. There is also another phenomenon called "crevice volume pre-ignition" that occurs when hot gases are trapped in the area between the spark plug center electrode and the plug shell. These gases can ignite the air-fuel mixture before the spark event, with a visual that looks kind of like a pre-chamber spark plug (flame blasting out of the plug firing end) when viewed with an in-cylinder camera.

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6 hours ago, v-rider said:

I think it would be clearer to put it this way: Low octane fuel can cause knock. (Knock occurs after the spark occurs.) Excessive knock can heat up the combustion chamber components so much that hot spots can eventually cause pre-ignition. (Pre-ignition means that the air-fuel mixture is ignited before the spark occurred at the spark plug gap.) That's the order of how it happens. In the automotive engineering world, we don't use the word detonation to describe anything like knock or pre-ignition. We really don't use the word detonation to describe anything...  

The line is getting blurred a little as there are recent findings that oil mist and carbon in the cylinder can also cause a phenomenon called "Megaknock". (This usually only occurs in turbocharged engines.) Megaknock is similar to pre-ignition in the fact that the cylinder pressure starts to rise quickly from combustion before the spark event. There is also another phenomenon called "crevice volume pre-ignition" that occurs when hot gases are trapped in the area between the spark plug center electrode and the plug shell. These gases can ignite the air-fuel mixture before the spark event, with a visual that looks kind of like a pre-chamber spark plug (flame blasting out of the plug firing end) when viewed with an in-cylinder camera.

The first couple of sentences basically just restate what I said.  Pre-ignition is caused by any condition that ignites the fuel prior to the intended ignition point.

However, while you may not use the word "detonation", that is precisely what "knock" is. "Knock" is the lay term for the audible sound fuel makes as it detonates, rather than burns.  Pre-ignition causes it for the same reason that too much spark advance does. 

The earlier in the burn the detonation happens, the worse it is because more fuel is involved.  Your "mega-knock" condition is simply that; detonation occurring very early on in the burn so that it involves a larger portion of the fuel charge.  Detonation events have been known to produce dramatic, even spectacular failures, bending connecting rods, breaking pistons and cranks, and blowing whole cylinders off engines.  It is often worse on supercharged engines since the whole idea of supercharging by any means is to force the engine to process a larger quantity of fuel. 

 

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      155 main jet
      200 main air jet
      EMN needle
      clip 3
      45 pilot jet
      2 turns fuel screw
      o-ring mod

      sea level,aftermarket pipe with open muffler-

      160 main jet
      200 main air jet
      EMN needle
      clip 3
      45 pilot jet
      2 turns fuel screw
      o-ring mod

      4000-600ft,stock exhaust or "quite,q,96db,corked up etc aftermarket pipe", 3x3 -

      145 main jet
      200 main air jet
      EMP needle
      clip 3
      45 pilot jet
      2 turns fuel screw
      o-ring mod

      4000-6000ft,aftermarket pipe with open muffler-

      150 main jet
      200 main air jet
      EMP needle
      clip 3
      45 pilot jet
      2 turns fuel screw
      o-ring mod

      In addition to the above or custom jetting, an extended adjustable fuel screw is highly recommended.
      Merge Racing makes a very nice one. What I like most about it is the Injection molded knob.. stays cool when the engine is hot, for easy adjustments. And because of its T shape is easier to grab with gloved hands and make adjustments.
      If not the Fuel screw from Merge, then any of the aftermarket screws not made from aluminum. Be very careful on the removal and install of the new fuel screw.. you have a small spring, washer and rubber O-ring that sits on the screw inside the body. One or more of these part sometimes remains in the body, and comes out haphazardly on the end of the old fuel screw. Very easy to lose one or more parts.

      The Fuel needle clip position is counted from the top, flat end of the needle. The needle pictured is in clip 3 position.


      Install tips

      No need to buy new throttle cables, the stock S cables work fine.
      Attach the throttle cables with the curved one on the bottom


      Hoses are routed like this



       
       
       
      It’s really not too short. People say this all the time due to the physical measurement between old carb set up and FCRMX being different, the FCR setup is slightly shorter. The air boot is plenty long enough. The preferred technique is to put the carb in the boot first. Then pull it forward to the manifold.
       
       
    • By mebgardner
      This "plug and play" kit has been developed so that the very fine Golan Mini Filter, 10 micron, can be fitted in-line to the KTM 690 Enduro & SMC motors, between the fuel tank and the injector, but can be easily accessed for cleaning and servicing without having to remove the airbox.
      It consist of a custom-built length of high-pressure OEM fuel hose, and OEM quick-release couplings and a Golan Mini Filter.This can be easily attached by disconnecting the OEM dry break and fitting our filter kit in between, and only requires the removal of the airbox once for fitting this kit.
      We have found the 10 micron Golan Mini Filter, which can be unscrewed and the filter washed, virtually removes any problem with injectors blocking, which can be a pain on long trips.
      Will work with or without our EVO1 & EVO2 tanks fitted.
      Suits all KTM 690 Enduro & SMC
    • By mebgardner
      Made in the USA !
      CJD-FFNK-690 Kit shown in all three colors =  KTM LC4 690 Enduro/SMC 08′-17′ ( Product show in picture is current ).
      The separate diamond shaped billet aluminum cover plate is now ALL ONE PIECE for aesthetics giving that OEM appearance on the 690.
      The stock KTM LC4 690/KTM 990 SMT fuel fill suffers from a few problems. The stock key lock system is susceptible to breaking keys, it also has a reputation for allowing dirt and grime in which is a huge problem on EFI systems and lastly the flip up cap can be cumbersome for filling with fuel or getting to your luggage. Our answer is a billet fuel neck that attaches directly to your gas tank, using the stock o-ring for a nice fit. Venting is done at the same 90 degree angle as OEM which eliminates having to use a breather vent cap. If you have removed the SAS system you can cap the body vent and vent from the top with a breather listed below.
      The fuel fill is CNC machined from ONE piece using aircraft aluminum, not a 2 piece welded part like others, and hard anodized. Specially crafted to replace your OEM system. No modifications to your bike or tank are necessary – simply remove the original and bolt ours into place.  Includes an Acerbis Viton sealed plastic fuel cap, which can easily replaced if need be. All hardware and mounting instructions included. Lightest kit on the market.
      Also works on your KTM 990 SMT with this style filler system.
    • By 230F
      Jetting the 230F
      By: Phil Vieira
      This project takes no less than 2 hours if you have never done jetting to a bike before. It took me 1.5 hours, to take my bike apart, take out the needle, change my pilot jet and the main, and take pictures along the way, but I have seen the inside of my carb 3 times, so I know my way around it pretty well…
      You should be jetting this bike right when you get it home. This bike comes lean from the factory. If you don’t know what that means, it means that the bike is getting too much air, in terms, a hotter engine, and your plugs will get hotter, and a decrease in HP. To make your engine last longer, do this.
      These jetting combos are for a 2000 feet and below scenario. Any altitudes higher, you should do a search on the forum. If it cannot be found, post on the forum. Please don’t post on the forum “How do I do this…” You have all the answers here.
      This project comes to a grand total of less than 30 dollars. The needle is 20, the main jet is about 3 dollars, and the pilot is 5 dollars. You may not need to do the pilot jet depending on your situation, but again, if you’re riding 2000 feet and below, it’s a good idea to get a pilot jet.
      The jets I used consist of a 132 main, 45 pilot and the power up needle with the clip on the 4th position.
      Part numbers:
      16012-KPS-921 – Needle (Includes Power up needle, Clip, and needle jet)
      99113-GHB-XXX0 – Main jet (Where XXX is the size)
      99103-MT2-0XX0 – Pilot jet (Where XX is the size)
      For the Jets, just tell them you need jets for a regular Keihn carb, (also known as a Keihn Long Hex) main jet size XXX, pilot jet size XX. They should know the part numbers. For the needle, bring the number along. If you are lazy, they should have a fiche and they can look up the numbers. Then again you can take in the old jets, and make sure they match up to the new ones.

      Now, the tools you will need are as follows:

      ~A collecting cup of some sort. I used a peanut butter jar.
      ~Ratchets for the following sizes:
      - 6mm, 8mm, 10mm, 12mm
      - Extension for the sockets needed
      ~Phillips and Flathead screwdriver (Be sure these are in perfect condition. A badly worn screwdriver will strip the screws)
      ~Needle nose pliers
      ~”Vise grips” or known as locking pliers (Two)
      ~Open end wrench 7mm and 12mm
      ~ It’s a good idea to have a extra hand around
      (Not needed, but I highly recommend tiny Phillips and flathead screwdrivers (Pictured next to the jar and the ¼” extension) I recommend these for removing a couple things since you can put pressure with your thumb on the end and unscrew it with the other hand. This insures that you will not over tighten any parts, and ensure that you will not strip the heads of the bolts.
      Ok, now that you have the tools, let’s start by putting the bike on a bike stand. I put it on the stand rather than the kickstand because it’s more stable and sits higher. I hate working on my knees. Start by taking the number plates off. Yes, both of them. The right side, you take off one bolt and the top comes off of its rubber grommets, pull the top off, and the plate comes right off. The left hand side, use the 10mm socket to take the battery bolts off, and then take the Phillips bolt near the back. Again, rubber grommets are used to hold the top in place. Take the seat off. There are two mounting bolts on the back:

      Those two bolts are both a 12mm socket. Use the open end wrench on the inside, and use the socket on the outside. You may need to use an extension if you don’t have a deep socket. Once you have the two bolts off, slide the seat back, and lift it up. This is what you have. Notice there is a hook in the middle and a knob on the tank. That is what you are sliding the seat off of.

      Now that the seat is off, you must take the gas tank off. Don’t worry, you won’t spill any gas any where, I promise. On the left hand side of the bike where the valve is, slide down the metal clip holding the tube in place. Turn off the gas supply, and slip the tube off slowly. Now take off the two bolts in the front of the take. This is on the lowest part of the gas tank in the front, behind the tank shrouds. The socket you will use is an 8mm socket. Take the bolts all the way off and set them aside. Now look back at the last picture posted. On the back of the tank, there is a rubber piece connected to the knob and the frame. Slip that rubber piece off of the frame. Pull the vent tube out of the steering stem and lift the tank up. Don’t tip it, and lay the tank aside where you won’t trip on it. This is what you’ll end up with:

      It may be a good idea to take a rag, and wipe all the dirt off the top of the bike if any. You don’t want anything dropping down into the carb. If you do, engine damage is the result. A clean bike is always a good thing! Now we must drain the gas out into that container. This is very easy. Make sure you open the garage door, windows, whatever, to let the fumes out. Breathing this crap is bad. Here is where the drain screw is:

      (Don’t worry about removing the carb, that comes later) This is on the right side of the carb, on the float bowl. The vent tube that goes down to the bottom of the bike is where the gas drains to. Put the jar under that tube and start to unscrew that screw, enough so that the gas leaks into that jar. Once the gas doesn’t drip anymore, close the screw all the way. Now on to the top of the carb. We are going to take this cover off:

      This cover comes off by removing the two screws. Once removed, the lid comes off as well as the gasket. Flip it over and set it aside. Do not set the gasket side down on the ground, as it will get contaminants! Here is what you are facing:

      The angle of the camera cannot show the two screws. But one is visible. It has a red dot, and opposite of that side is a darker red dot. I made it darker because it’s not visible, but that is where it is. This is where I use the miniature screw drivers to get the screws. I magnetize the screwdrivers, and use care to make sure I don’t strip the heads. Metal pieces in a piston are not good! Remove the two screws. Put these screws on a clean surface so they do not get contaminants. Now get your vise grips and set it so that it will lock onto the throttle, not too tight, not too loose. Set the vise grips on the seat. Start to open the throttle slowly as you guide that “plunger holder” (as I call it) up to the top. Once you have the throttle all the way open, take the vise grips, and lock it so that the throttle does not go back any more. What I do is I hold it pinned and lock it up against the brake so it doesn’t rewind on me. If you don’t have locking grips, a friend will do, just have them hold the throttle open all the way until you are finished. How fold the plunger holder to the back of the carb and pull the piece up to the top. Take care not to remove it, as it is a pain to get back together! If it came apart on you, this is what it should be assembled to:

      Once you get the holder out of the slider, set it back like this:

      As you can see, the bar is back 45 degrees, while the holder is forward 45 degrees to make a S. Here is what you are faced with when you look down on the carb:

      Where the red dot is where the needle lies. Grab needle nose pliers and carefully pull up the needle out of its slot. This is what the needle looks like once it is out.

      Now we must move the carb to take the bowl off. Untie the two straps on the front and back of the carb. Don’t take them off; just loosen them until the threads are at the end. Take the front of the carb off the boot and twist the bowl as much as you can towards you. Tie the back tie down to that it does not rewind back on you. This is what you have:

      Now we must take off the bowl. Some people take that hex nut off to change the main jet, which you can, but you cannot access the pilot jet, and you can’t take out the needle jet (a piece the needle slides into), so we need to take it off. It’s just three bolts. As we look at the underside of the carb, this is what you will see:

      The bolts with the red square dots are the bolts you will be removing. These are Phillips head bolts, and the bolt with the blue dot is your fuel screw. This is what you will adjust when the time comes, but keep in mind where that bolt is. You need a small flat blade to adjust it.
      Well, take those screws off, and you are faced with this:

      The blue dot is for cross reference, which is the fuel screw once again. The green dot is the pilot jet. You can remove this using a flat blade screwdriver. Just unscrew it and pull it out. Once you pull it out, set it aside and put in the 45 pilot jet you got. The red dot is the main. You remove this by using a 6mm socket. Just unscrew it. If the whole thing turns, not just the jet, but the 7mm sized socket under it, don’t worry, that piece has to come out as well. If it doesn’t, use a 7mm to unscrew it off. Here is what the jets look like:

      Pilot Jet

      Main jet attached to the tube. Take the main jet off by using an open end wrench and a socket on the jet. Again, it screws right off.
      Here is what you are faced with if you look form the bottom up.

      From left to right: Main jet, Pilot Jet, Fuel screw. Now in the main jet’s hole, if you look closely, you see a bronze piece in the middle of that hole. We are going to take this off. Since I did not do this part (I only changed my pilot jet when I took these pictures) there are no pictures taken for this section but this is really simple to do if you’ve been a good student and know where things go. You should know anyways, you have to put the bike back together!
      (Notice: There have been discussions about these needle jets being the same. Only change this needle jet if the one you have is worn out. If you do not have the old needle, a older drill bit bigger than 3/20ths (.150), and smaller than 11/100 (.11") Use the tapered side of the bit, set it down in the hole and tap it out carefully.)
      Now take your OLD needle, I repeat, the OLD needle because what you are going to do next will ruin it. Pull the clip off with your needle nose pliers, or a tiny screwdriver to pry it off. Then put the needle back in the hole where it goes. That’s right, just to clarify, you took off the needle, and you put the needle back in the hole with no clip. Slide the point side first, just as it would go normally. Now if you look at the bottom of the carb, the needle is protruding past the main jets hole. Grab another pair of locking pliers (vise grips as I call them) and lock it as tight as you can on the needle. Pull with all your might on the needle. Use two hands. Have a friend hold the carb so you don’t pull it off the boot. Tell them to stick their fingers in the hole that goes to the engine, and pull up. After pulling hard, the needle jet should slip right off. Then notice which side goes towards the top of the carb. There is one side that is a smaller diameter than the other. Take the new needle jet, and push it up into the hole the way the old one was set. Just get it straight. Take the tube the main jet goes into, and start threading it in. Once you can’t tie it down anymore with a ratchet, unscrew it and look at the needle jet to make sure it’s set. That’s it for the needle jet. Now let’s start putting the carb back together.
      (Notice: Many people have destroyed jets and such by overtighting them! Use the thumb on the head of the wrench and two fingers on the wrench to tighten it down.)
      Thread the main jet into the tube it goes into, and then start putting it back on the carb. Thread the pilot jet in as well if you haven’t done so already. Remember these carburetor metals are soft as cheese, so don’t over tighten the jets very much. What I do is I put my thumb on the top of my ratchet, and use two fingers closest to the head of the ratchet to tighten the jet. That’s how tight I go when I tie them back in.
      Now before we put the carb back together, let’s adjust the fuel screw. Take a small screwdriver, and start screwing in the fuel screw until it sets. Again, do not over tighten, just let it set. Then count back your turns. Count back 1.75 turns.
      Now we must put the bowl back on. The white piece that came off with the bowl goes back as followed:

      If you look directly under the carb, the round hole is aligned with the pilot jet. Take the float bowl, and put it back on.
      Untie the rear clamp and the front clamp as well. Slip the carb back the way it used to. Make sure that it is straight up and down with the rest of the bike. The notch on the front boot should be aligned with the notch on the carburetor, and the notch on the carburetor should be in that slot. Tie the clamps down securely.
      Let’s put the needle in. These are how the needle numbers go:

      The top clip position is #1, the lowest one, closest to the bottom, is #5. (The picture says six but it is five in this case) For reference #1 is the leanest position, while 5 is the richest. I put the clip in the 4th position. Read at the bottom of the page and you can know what conditions I ride in, and you can adjust them to your preference.
      Put the clip in the new needle, slip it in. Take the vise grips off your grips and start guiding the plunger holder down to the bottom. Remember not to let that assembly come apart because it is a pain in the ass to get it back together! Once you get it to the bottom, put the two screws on, and then put the cover on.
      Now that you have done the carburetor mods, there is still one thing you want to do to complete the process. Don’t worry, this takes less than a minute! On the top of the air box there is a snorkel:

      As you can see, you can slip your fingers in and pull it out. Do that. This lets more air in to the air box. Don’t worry about water getting in. There is a lip that is about 1/8” high that doesn’t let water in. When you wash, don’t spray a lot under the seat, but don’t worry about it too much.
      The next thing you must do is remove the exhaust baffle. The screw is a torx type, or you can carefully use an allen wrench and take care not to strip it:

      The screw is at the 5 o’clock position and all you do is unscrew it, reach in, and yank it out. This setup still passes the dB test. The bike runs 92 dB per AMA standards, which is acceptable. Just carry this baffle in your gear bag if the ranger is a jerk off. I’ve never had a problem, but don’t take chances.
      That’s it! Start putting your tank on, seat, and covers. After you put the seat on, pull up on the front, and the middle of the seat to make sure the hooks set in place.
      Turn on the bike, and take a can of WD-40. Spray the WD-40 around the boot where it meets the carburetor. If the RPM rises, you know you have a leak, and the leak must be stopped. You must do this to make sure there are no leaks!
      Here is my configuration:
      04’ 230F
      Uni Air filter
      132 Main Jet
      45 Pilot Jet
      Power up needle, 4th clip position
      Fuel screw 1.75 turns out
      Riding elevation: 2000ft - Sea level
      Temperature – Around 60-90 degrees
      Spark Plug Tips
      When you jet your carb, a spark plug is a best friend. Make sure your spark plug is gapped correctly, (.035) but that’s not all that matters. You want to make sure the electrode is over the center, and you want the electrode to be parallel, not like a wave of a sea. Put in the plug, and run the bike for 15 mins, ride it around too then turn it off. Then take off the spark plug after letting the bike cool. The ceramic insulator should be tan, like a paper bag. If it is black, it is running rich, if it is white, it is running lean. The fuel screw should be turned out if it is running lean, and turned in if it is running rich. Go ¼ turns at a time until your plug is a nice tan color.
      Making sure your bike is jetted correctly
      While you are running the bike for those 15 mins to check the plug color, you want to make sure it’s jetted correctly now. Here is what the jets/needle/screw control:
      0- 3/8 throttle – Pilot jet
      ¼ to ¾ throttle – Needle
      5/8 – full throttle – Main jet
      0-Full – Fuel screw
      Pin the gas, does it bog much? Just put around, is it responsive? When you’re coming down a hill, the rpm’s are high and you have no hand on the throttle, does it pop? If it pops, it is lean and the pilot jet should be bigger. If it’s responsive your needle is set perfectly. You shouldn’t have to go any leaner than the 3rd position, but I put mine in the 4th position to get the most response. Your bike shouldn’t bog much when you have it pinned. If it does it is too rich of a main jet.
      Determining the plug color, you will have to mess with the fuel screw.
      That’s it, have fun jetting, and any questions, post on the forum, but remember to do a search first.
      Also, if your bike requires different jets due to alititude, humidity, or temperature, please post the following so we can better assist you:
      Average temperature
      Altitude (If you do not know this, there is a link in the Jetting forum that you can look up your alititude)
      Average Humidity
      What jets you are currently running
      What the problem is (If there is one)
      Just do that and we'll help you out the best we can.
      EDIT: The girl using this login name is my girlfriend. You can reach me on my new login name at 250Thumpher
      Then again, you're more than welcome to say hi to her!
      -Phill Vieira
    • By Red_250X
      Just wanted to give you X fans some real world successful jetting settings. I just got back from a trip to Colorado and wanted to share these settings.
      Our camp was at 6100' and we rode up to 13,000'. Temperature was between 65 and 85 (absolutely PERFECT!).
      Modifications:
      Airbox opened about a third of CCC recommendations.
      Baffle removed, but spark arrester in place.
      Pilot jet changed from 40 to 42.
      Setup:
      -Needle in stock position
      -Main jet - 142
      -Air screw at stock position (I probably could have made some improvement, but I was having too much fun riding and I didn't experience any hesitation)
      The bike ran great and climbed some HUGE hills. Most of our riding was single track, switchbacks, very difficult and technical - a lot of 1st and 2nd gear.
      NOTE!! Apparently, the 250X is jetted lean in stock form. Opening the airbox and removing the baffle leans the carb even further. IF YOU DO THESE MODS, REJET YOUR CARB!!! Otherwise you could do serious damage to the motor. It will run significantly cooler when it is not lean. I live at about 600' and am running a 152 main jet.