Recently bought an 03 KDX220R. The guy I bought it from said he gets the best results with 87 octane.......I was like "what the hell???". Is there any resaon for this to be true ??? I've always used 93 in my YZ's. Just talk among yourselves and I'll sit back and soak up all the knowledge....thanks guys .........and gals !!!
93 octane.....pros vs cons?
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OLHILLBILLY
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- Jun 29, 2006
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I run 91 pump in my '04 200 and it works great. Used to use 93 in my YZ too, though I did run 91 in it a few times and couldn't tell any difference between it and the 93. All I did was ride in the woods though, MX might be a different story.
One other side note. If your getting your gas out of the station pump, run a couple of gallons into your car/truck first. Otherwise at least a gallon of what your putting into your pre-mix can will be 87 out of the hoses and internals of the pump before it gets the higher octane to the nozzle.
One other side note. If your getting your gas out of the station pump, run a couple of gallons into your car/truck first. Otherwise at least a gallon of what your putting into your pre-mix can will be 87 out of the hoses and internals of the pump before it gets the higher octane to the nozzle.
Octane is simply the ability to resist detonation. Like Julien said, if it's not pinging it should be fine. I've always run premium in all my bikes because it only costs an extra dollar to fill the can and it's cheap insurance. Detonation can be really hard on the engine.
gwcrim said:
No you don't. :rotfl:
I defy you or anyone else that feels compelled to preach this nonsense to show the slightest real proof that this would be the case. Even the most casual review of basic combustion chemistry would show the flaws in this thinking.
I'm always up for being better educated, so .... educate me. ;)
gwcrim
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OK.... many years ago there was a series of articles in Super Stock and Drag Illustrated penned by Bret Kepner under the ghost name of 'Dr. Dirt' if I recall correctly. Bret is a very talented drag racer. He documented how he could use a rent a car in a bracket race and win over a full out drag car. I mean, he had it down to knowing the amount of time he could scrub off by drifting the car from the middle of his lane to the outside.
One of his tricks was this: If he needed to slow a few hundredths in a race, he would take a bottle of octane boost and add it to bone stock street car. His assertion was that the fuel, now being a little less volatile, would ignite a little later and throw off the timing just enough to slow him down by a few hundredths.
This is a guy who had made thousands of passes down a drag strip and documented nearly every one. I'm sure you know how much meticulous record keeping is to a bracket racer. I think he was onto something.
Another racer that I know, Aaron Wilson of Team Elves land speed racing fame, builds his engines around the fuel he will be using. We have had several conversations regarding fuel and he agrees. This is a guy who got a Sportster powered Buell to nearly 220 MPH. He's experienced with nitromethane and nitrous as well.
I'm not saying that using more octane hurts anything. But if the engine compression and timing is optimized to run 82 octane pump swill, don't you think that using a less volatile fuel would change it's power output some?
One of his tricks was this: If he needed to slow a few hundredths in a race, he would take a bottle of octane boost and add it to bone stock street car. His assertion was that the fuel, now being a little less volatile, would ignite a little later and throw off the timing just enough to slow him down by a few hundredths.
This is a guy who had made thousands of passes down a drag strip and documented nearly every one. I'm sure you know how much meticulous record keeping is to a bracket racer. I think he was onto something.
Another racer that I know, Aaron Wilson of Team Elves land speed racing fame, builds his engines around the fuel he will be using. We have had several conversations regarding fuel and he agrees. This is a guy who got a Sportster powered Buell to nearly 220 MPH. He's experienced with nitromethane and nitrous as well.
I'm not saying that using more octane hurts anything. But if the engine compression and timing is optimized to run 82 octane pump swill, don't you think that using a less volatile fuel would change it's power output some?
gwcrim said:
You are working under a fundamental misconception here. The volatility of a fuel is determined by it's distillation curve and the Reid Vapor Pressure. You can have two fuels with the same distillation curve (volatility) yet wildly different octane ratings, and they will make the same power.
On the flip side, you can have two fuels with the exact same octane spec yet very different distillation curves and volatility characteristics, and they can potentially make different power and have much different throttle response.
The distillation curve of a fuel is critical to performance and good tuners match the fuel's curve to the engine spec and more importantly the engine application.
Two fuels with the exact same pump octane number can have very different knock characteristics in a running engine if the distillation curve is modified certain ways. This is especially true in two-strokes where a change in the tail end of the distillation curve can be used to provide piston crown cooling and help control some of the precursors of detonation.
Octane rating is just a very small and mostly over-rated part of a the fuel picture. A fuel's 10-50% temps on the distillation curve and the shape of the curve will have a huge influence on throttle response, and the 90% to end point temps will have an influence on piston cooling in two-strokes and high rpm (over 6000 rpm) power in all engines.
In the case of the original poster's question.
The only consistent advantage of running 87 octane is cost. The obvious downside being an engine that works well on 87 octane today may see a variance in fuel week to week, or a change in operating conditions that makes 87 octane inadequate. Once that happens two-strokes get destroyed pretty quickly. Seems to me like a foolish way to save money.
The only downside I can see to running premium (93/91) other than cost is the chance that in you area premium will have a higher percentage of Ethanol. This poses a problem for a couple of reasons. Ethanol has a fixed boiling point, so large quantities have a major influence on the fuel's distillation curve, and the blenders have to account for this in other ways. For high speed engines (like motorcycles) that see major swings in rpm and throttle openings, this is a bad thing. Closed loop EFI cars (the intended market for pump fuel), have long very hot intake tracts and run much lower rpm, with much smaller, less frequent throttle transitions, so it's not a problem.
Ethanol also has an impact on the octane distribution within the fuel's distillation curve. This can cause knock issues in some cases.
The moral of the story? If you have any sense you'll run something other than that swill they pump at the local gas station. :) Seriously, if you are running pump fuel run the highest octane you can get and give yourself the safety margin it provides. It's cheap insurance.
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OLHILLBILLY
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- Jun 29, 2006
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Totally different deal I know but.. It's a well documented fact that using pump 91-93 octane in a stock compression Hayabusa motor will carbon up the exhaust valves almost like running 40:1 pre-mix in them would. 87 octane will yield a clean motor that doesn't ping and will run 80,000 miles with no issues. I've always understood that higher octane gasoline just burned a little slower than lower octane fuels making pre-ignition (ping) harder to happen. Thus the dirty combustion on the Busa motors using higher than required octane fuel.
I dunno, but I go along with the theory of higher octane fuel (in a motor that doesn't require it) will make slightly (probably very slightly) less power than the correct octane, simply due to the slower burn rate.
Back to the KDX. In the woods, on a HOT summer day, in the wrong gear, motor lugging, me struggling (as I so often do ;) ) I prefere the higher octane safety margin the 91 provides. 1/2 HP be damned, I want to make it back to the truck. :cool:
I dunno, but I go along with the theory of higher octane fuel (in a motor that doesn't require it) will make slightly (probably very slightly) less power than the correct octane, simply due to the slower burn rate.
Back to the KDX. In the woods, on a HOT summer day, in the wrong gear, motor lugging, me struggling (as I so often do ;) ) I prefere the higher octane safety margin the 91 provides. 1/2 HP be damned, I want to make it back to the truck. :cool:
OLHILLBILLY said:
With all due respect, the octane rating of a fuel will give you no indication of the combustion speed .
It’s common practice for writers in popular press to summon the gods of combustion speed to try and explain the magic powers of octane rating. They prattle on about race gas, toluene, acetone, any number of octane boosters and Home Depot speed secrets and the "burn speed" on a receptive but otherwise unknowing audience. They’ll tell you that these compounds raise the octane of the fuel and as a result slow down combustion and fend off detonation as a result. It’s just more pseudo-science BS from people who would have done well to pay more attention in Chemistry 101 in high school.
Real combustion events follow the real laws of chemistry, and while it’s a pretty complex set of interactions there are a few things that are easy to explain and understand.
Due to lots of magazine guys spreading incorrect info over the years it's a commonly held misconception that higher Octane fuel slows down the flame speed, which keeps the engine from knocking. Sorry, but that's a load of crap.
A fuel's laminar Flame speed (basically fuel burning without the influence of combustion swirl or tumble) is a function of fuel chemistry (specifically Hydrogen/Carbon ratio), not the Octane rating.
The Hydrogen/Carbon make up of the fuel will determine it’s flame speed and the energy release whether it's a high-octane fuel or not. You can have fast and slow burning high octane fuels, but in most cases the differences are so slight as to not be an issue.
The heat of combustion at a simple level is basically a function of combustion efficiency and the calorific (energy) value of a fuel. There isn't a lot of energy difference between most conventional fuels, but combustion efficiency can sometimes be improved with race fuels so a bit more heat release is possible. Overall it's pretty much a wash in most cases though.
In other words, you aren't going to change the energy release or the speed of combustion in any significant way by switching from 87 to 110 octane gasoline, or anything in between . If you lose or gain power by switching fuels there are other things at work. The influence of the distillation curve we discussed earlier being a major influence.
The way octane influences knock has to do with the way fuel is burned (well it’s really chemically REACTED) in the combustion chamber. The components in higher-octane fuels are less likely to have weak molecular bonds that can break easily and form active radicals. Higher-octane fuel is just made up of components that are (for lack of a better term) stouter under high temperatures and high cylinder pressures. Things like our long lost friend lead and metallic additives like MMT (common in octane boosters) tend to work as an anti-catalyst and block the formation of the active radicals that lead to auto-ignition of the fuel and ultimately detonation. The longer it takes to react all the fuel the greater the chances are that heat will accelerate the reactions beyond what the fuel components can bear. The idea that purposely SLOWING things down in the chamber is somehow beneficial in light of the reactions taking place is pretty funny really
Heat , pressure, and time tend to be the driving force in all of this. The more heat and pressure you subject the fuel to and the longer you keep the temps elevated the better and more stable the fuel you need . That's part of the reason why engines that run at high rpm and have small bores can run very low octane fuels even with high compression ratios and not suffer knock while lower rpm engines with bigger bores need comparatively higher octane ratings for the same compression ratio.
It's just simple chemistry really. If you look at the chemistry of explosives you can see a lot of similar reactions taking place, and it can give you some real insights into what's happening inside the combustion chamber when things go wrong. It's a fine line between engine tuner and explosives engineer.
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OLHILLBILLY
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So I guess the question now would be, "do we know any more than we did before?"
In my case at least, the answer would be, "no".
Wanders off, totally confused and mumbling to self.
In my case at least, the answer would be, "no".
Wanders off, totally confused and mumbling to self.
nsxxtreme said:
I was sitting on a conference call I didn't need to be on and I was bored to death. This seemed like a reasonable diversion. ;)
OLHILLBILLY
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Patman said:
So now I'm worthless.
I'll not offend everyone else and get into trouble on the board describing what I think of you.
- Dec 26, 1999
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Did I say YOU were worthless? No I believe I said that a closed mind is worthless which it is, much like the value of a book is only there when it has been opened. The original form is a Chinese proverb "A closed mind is like a closed book just a block of wood." so I guess if you feel better being a block of wood then feel free to superimpose that on to yourself. I realize it's always much easier being a martyr but if you decide to offend everyone else and try to make me weep in the corner feel free to do so, I'll be napping on the couch try to make up for all the sleep I'm sure I'll lose over your comments. :laugh:OLHILLBILLY said:
OLHILLBILLY
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Patman said:
Yes, with the wording of the reply I'd say you did.
But in the end superdude, I'll give you the win, your Holier than I. Let me be the first to congratulate you on your self imposed superiority. (naughty word / personal attack).
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dansavage said:
Thanks Dan. :cool: I didn't recognize 2,5-dimethylpentane.
2,3-dimethylpentane & 2,4-dimethylpentane were the only ones that weren't covered with rust and clicked in my head. :whoa:
So I just spent the last hour or so grinding through books scattered across my living room floor, reacquainting myself with the nuts and bolts of alkylation, and general refinery processes. I'll be the life of the party this weekend. :whoa: :rotfl:
2strokesrock
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- Oct 7, 2008
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This has been a REALLY interesting thread :) but I want to make sure I understand it.
Octane: Is basically the fuels ability to resist heat (I know there is more to it than that but...nvm)
So high octane is needed in high compression engines to prevent premature combuston do to the excess heat of rapidly compressed fuel..right?
so...what about diesel? does that mean that diesel has even greater heat resistance?
Octane: Is basically the fuels ability to resist heat (I know there is more to it than that but...nvm)
So high octane is needed in high compression engines to prevent premature combuston do to the excess heat of rapidly compressed fuel..right?
so...what about diesel? does that mean that diesel has even greater heat resistance?
