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AV fuel for XR400 100 low lead.

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Hello gents,

I was wondering if anyone out there would be willing to comment with regard to the use of Aviation fuel i.e. low lead 100 octane gas. I have heard a few things about the use but was wondering if anyone out there has or does currently use this sort of fuel with/in their XR400 (primarily). I am also interrested in any pro's or cons of use of said fuel. Thanks in advance for anyone who responds with first hand experience or input in general.

-Slider69 :)

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I may be wrong, but I think the difference is race fuel has lead in it which is needed for high compression engines.

correct me if I'm wrong :)

John

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The higher the cotane the sooner you will have to replace your top end. You may get some addition power but not alot. 93 octane pump gas soots me just fine. The only reason pors run higher octane is because they dont need to pay for it and their top ends are free. If i was you i would stay with 93. Good Luck!

-----------

1987 Xr250r- 909 Team talls, Millville tires, maier

plastics, ufo universal mx fender, cycra bark busters, k&n airfilter,white brothers e-series, snorkel removed 280cc big- bore kit, and many more experiments.

1961 Honda 90- Totally stock and she still rips!

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In cars, the lead is needed in older engines to prevent valve seat errosion because the seats were not hardened. Newer engines already have the hardened seats, so unleaded is is fine. Excess octain is really wasted and can actually overheat the exhaust system.

PD

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I always love it when this thread comes up because the posts always contain some outlandish claims. They usually read like " burning up your top end"....... to "....... 10 horsepower gains","wheelies forever" but thats what makes the forums so fun!

Avgas is misunderstood because it isn't car gas and most people have no experience with it so they just fill in the blanks. 100 low-lead is formulated to run in aircraft specifically and it is much more refined ( cleaner ) and regulated than autogas. Contrary to popular belief, most aircraft engines are not high compression, high power machines. They (most) are simple, air-cooled four strokes!

Avgas burns hotter wich helps the motors run cooler. Remember, low octane raises cylinder temps. up to the point of detonation/failure. As for a stock XR400, nothing/very little is gained with 100LL.......its just expensive gas going out the tailpipe. My 440 has an 11:1 piston an runs quite happy on Avgas vs. pump gas. I work on airplanes for a living and often I get my hands on sumped gas and throw it in the bike. Ive used Avgas in my XR650R since day one even though it doesn't need it, I just like the fact that it is soooo clean. It (the 650) was designed to run on 91/92 and Team Honda runs thiers on 92 octane even though they could afford any gas on the planet. They don't need it.

This same subject came up on the Yahoo 650R page and a fellow from Europe posted a service bulletin from the Austrian engine builder Rotax that said 100LL should not be used in thier four-stroke motors because of possible deposits building up on the valves, so I guess the jury is still out on Avgas.

I just did a top-end on my 650R more for boredom than anything and I can tell you the valves were almost spotless! Long live the blue juice.

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This Guy Doesn't Sound Like Hes Knows What Hes Talking About. Yeah Right! Thanks For The Info. This Same Conversation Comes Up When I'm With My Fellow Riders All The Time And Now I Can Tell Them They're All Full Of Bs! Thanks A Lot

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There's a guy here in geralton who has a 440 big bore kit with the 12.5:1 compression ration piston, and he found that he had to use the Aviation fuel so it would not ping.

He got it from the airport. I dont think you can get it anymore here though.

I havnt heard anymore from him than that.

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i have used a 50/50 mix, av gas and premium pump gas and it worked fine for me. it burns cleaner and doesn't put out the black spooge on two strokes and you don't get the black soot in the tail pipe of the four strokes. the bike will run smoother for you when you are lugging it. i don't run it now just because i am too lazy to walk out to the pump with a five gallon can to get it.

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Thanks to all that replied. I will probably try it out and get some first hand info. If I like what it does I will probably use at least a mix. If not back to the 92 octane premium pump grade.

Thanks again.

-Slider69 :)

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AV fuel is formulated differnt then pump gas.....1. To run at steady engine speeds. 2. High altitude. 3. Cold temps. If you want to run higher octane buy a booster or race gas. Higher octane wont make your motor make more power then it can...this can only be done with mods. 93 pump gas will run a well tuned high compression motor fine....the key is "well tuned". I guess AV fuel would be fine if you plan on riding fireroads.....in the mountains.....in Antarctica.

Steve :)

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The only reason to run a higher octane fuel is to prevent detonation! If you dont understand detonation then you need to go here and read all about it.

http://www.motorcycle.com/mo/mcrob/rt-fuel2.html

This article will educate you more than you may want, but at least the ones claiming that AVgas will give you more HP will figure out that they don't know what in the world they are talking about!

my 2 cents!

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Actually, the higher the octane, the cooler the engine runs. On long races this is important where the temperatures run high, i.e. long sandwashes, long sustained high rpm running on straightaways and so forth. XRs all run good on 91 octane (or for that matter any octane lower too). The need for higher octane comes from running engines that are ported, built (12:1 or higher) and need a cooler fuel to keep from overheating. The < lower the octane, the hotter it will run, not the other way around. Same as plugs, lower plug reading, hotter plug. Higher plug, cooler heat range. Keep AV gas to airplane engines.

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ok so tell me why the engine runs cooler due to the octane rating? you missed the point here. I guess you're too smart to read the article that was posted. The higher octane rating actually reduces the tendancy of fuel to combust before it is supposed to. In short the higher the octane rating of a gas means more energy is required to make it burn. In a stock low compression engine this is not even a problem, so the octane rating of avgas will not affect the engine temps the way you suggest. But if you start boosting the compression ratio's then you will need the higher octane rated gasolines to prevent detonation. Go read the article, there is nothing to be learned but knowledge. Octane rating does not need to be a mystery, but you need to be educated to know when a higher octane fuel is necessary and when it isn't.

http://12.215.122.222/gas.htm

http://12.215.122.222/Racefuel.htm

http://12.215.122.222/Detonation2.htm

http://www.aircooled-rd.com/default.asp?txtPage=squish1.htm

A lot of this stuff is written with 2-strokes in mind, but the physics behind the articles is sound. There is a lot to be learned here if you want to take the time to do it, or you can keep spending unnecessary money on gas you don't need.

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Hey PilotHawk, I think HuskyForever is agreeing with you.....By the way higher octane doesnt "take more energy to burn", it just releases its energy slower...ie. burns slower. Detonation is the result of fuel burning to fast or even at the wrong time in the cylinder. You are right about octane not making more power .....it wont make any more then the motor can make. Go do a shot of octane and cool off.

Steve :)

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More energy is required to make it burn.

The higher octane makes the fuel harder to ignite at cylinder pressures than it would be to ignite a lower octane fuel.

I am not lashing out. I just want to help you guys understand the physics behind what makes these things go.

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OK.....Think I kinda understand the physics of how things burn....Its kinda what I do everyday. Firefighter/Hazmat Tech.....Thanks for the info.

Steve :)

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OK.....Think I kinda understand the physics of how things burn....Its kinda what I do everyday. Firefighter/Hazmat Tech.....Thanks for the info.

Steve :)

lol :)

i always phrase it as, "octane is a measurement of a fuel's resistance to burn." octane is the name a molecule with 8 carbon atoms. the benefit of higher ocatnce is only necessary on high compression engines as already mentioned. it resists pre-detonation (pinging or knocking) and can provide better performance because it burns slower...a slow, steady, controlled burn for hopefully the entire piston travel of the power stroke.

as far as octane's effects on engine temperature, that is a totally new one on me. i will examine some of the links provided...hehehe probably at work!

good info in this thread...but i dont think Avgas is going to give you any noticeable advantage over pump gas, unless you have a REALLY modified engine or REALLY want to split hairs on a some dyno chart.

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This sort of ties in with the issues Subaru Impreza turbo drivers have in the UK,if 95ron pump fuel is used (the most common available) the cars' ecu will detect this and retard the ignition to prevent det. and the car produces less power,if 97ron is used the ecu recognises this and will over a few tank fulls adjust the ignition forward ,hence providing more power :):p .[i'm not saying higher ron =more power :):D ]

This obviously is not transferable to an xr400 but the xr does seem to idle better run smoother and seem, well , just sweeter on 97 ron ,even if not any quicker, although this may be my imagination but i think not :D

Has anyone else found there bike runs 'sweeter' (ignoring power) on higher ron ,avgas or not...

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I disagree with some of this info.

The octane number does not describe how quickly the fuel will burn or how much potential energy it contains, etc. There are higher octane fuels available that actually burn faster than lower octane fuels and visa versa, but the flame speed itself is a function of chemistry and not octane.

The term octane describes the grade of gasoline and its resistance to engine knock (automatically ignite) and the only time your engine is aware of octane is when it doesn't have enough. The total energy in BTU's for a given fuel can also be a misleading. A fuel rated with more BTU's may have more energy potential, but that doesn't mean it's all usable or usable within a certain range. The distillation curve defines the temperature at which various amounts of gas is vaporized. Generally, the race fuels for our motorcycles that offer more power with improved throttle response vaporize at lower temperatures and the distillation curve of a fuel can help clue you into good fuel choices for specific applications.

Here's yet another excellent technical resource for fuels.

http://www.rockettbrand.com/technicals/bulletins.htm

Here's two excellent articles concerning fuel.

http://www.ericgorr.com/techarticles/Fuel_Basics.htm

http://www.ericgorr.com/techarticles/fuel_terminology.htm

There's also a great deal of excellent tech info about fuels here on TT. If you do a search for "Rich_Rohrich" here on TT and read some of his older posts about fuel, you'll find a wealth of info on this topic.

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Pilothawk, he asked for the pros and the cons in regards to everything, which octane levels apply too. Someone else mistakenly thought the higher octane, the higher tempeture. You want to run AV fuel, go for it. I was just pointing out something else from a class given by Union 76 wizards to us mortals a year ago on fuels and octanes. :)

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