Thank you, Thank You, Thank you! I've had similar discussions on three different forums (Mercedes, BMW & Acura) and nobody has yet summed this up so eloquently in such a brief period. Can I quote you outside this forum?Let me be the first to dispel some rumors on octane here.
Myth: Higher octane in a given motor will give more performance.
Truth: Engines are tuned from the factory to run a particular octane. Octane is simply (without going into the mechanics of it) the rate at which the fuel will burn and its resistance to detonation as pressure builds. An engine tuned for higher octane will have its ignition timing retarded to take advantage of the more stable fuel, and also have higher mechanical compression ratios built in. Cam timing is usually set to allow higher cylinder pressure, which in turn requires stronger rods, pistons, etc... Now, an engine tuned for 87 Octane will run worse generally with higher octane fuel. The reason is the fuel will not completely combust because of the slower burn time, and allow maximum cylinder pressure as a result, equalling less horsepower. The fuel is typically ignited BEFORE the piston reaches TDC and maximum cylinder pressure ideally reached just as the piston begins the downstroke. If you use fuel that burns slower than the engine is tuned for, maximum cylinder pressure will not happen until well after the piston is moving down the cylinder, meaning you will not get the "bang" for your buck so to speak.
Equally, by using a lower octane fuel than a motor is tuned for, the fuel could detonate or burn to quickly, causing cylinder pressure to max out before TDC, resulting in tremendous strain on the engine and possibly scattering it (this is why many people who use nitrous and dont tune for it end up with a pile of parts, but I digress...).
In short, unless you know what you are doing and retune for higher octane, use what the manufacturer recommends. Sorry for the long post.
Absolutely. I actually used to work as a Mercedes Benz technician. I have been a student of high performance since 16 years old and I still learn every day. This is one of those big misconceptions people have out there (there are many). Hope it helps some people out.Thank you, Thank You, Thank you! I've had similar discussions on three different forums (Mercedes, BMW & Acura) and nobody has yet summed this up so eloquently in such a brief period. Can I quote you outside this forum?
You won't get pre-ignition using the higher octane, you get that using lower octane. With the higher octane you get detonation from the flame coming late after the piston has started downward(like Roughneck explained) thus the flame has to 'catch' the piston which can cause nasty issues when they collide. The higher octane fuel is more stable to pre-ignition thus why it's used in higher compression engines because the air is heated by compression and low octane fuel can actually start combusting before the spark merely from the compression heat. This is the principal a diesel operates from. The higher octane fuel may not burn completely which also has it's drawbacks. Higher altitudes often don't need as much octane because the air is a lot thinner at the higher alt's which in effect lowers the compression of the engine.Due to altitude gas in utah is different, our regular is 85 and premium is 91. Since I live at 5000' and ride mostly in the mountains up to around 8000' I run 85. I experiance preignition Roughneck is talking about every time I run 91. When I get over 6000' it happens with 87 so I ignore the manufactures recommendation. The loss of power is real; I feel like the bike is bogging anytime I give it gas -- I can do ok easing on the throttle.
Octane rating method method is different in the North America as compared to most of the world.never heard of 89 in uk we have 95 or 98
Two reasons gas costs so much in Europe: extremely high taxes and they way they refine to obtain a much higher percentage of Diesel fuel from a barrel of oil than does the US.Goon,
Maybe that answers part of the question why gas in Europe costs so much more than in the U.S. There may be a few cities where you can find 98 Octane but I don't think it's standard in any state.