Quote:
Originally Posted by ninjaguy500
OK, been reading all of this, and was told by the service tec at my local Honda dealer that I needed to run 93 if I was not able to get anything but methanol, and have been running nothing but 93 since I got my Yamaha since we converted our station from conventional gas. I was also told to only run 93 in my mower, weedeater, blower and chain saw instead of 87 methanol. Any feelings on this. I also have started running plus in my Toyota, because the engine would knock with the methanol, and I have noticed a 5-7 mpg loss.
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As was discussed earlier in the thread, what your manufacture suggests is probably the best thing to use in a stock bike. If you've made engine changes, such as higher compression pistons, shaving the heads, using thinner head gaskets, etc. then the higher octane is probably called for.
Higher octane ratings correlate to higher activation energies. 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 autoignition.
It might seem odd that fuels with higher octane ratings are used in more powerful engines, since such fuels ignite less easily. However, an uncontrolled ignition is not desired in a spark ignition engine.
A fuel with a higher octane rating can be run at a higher compression ratio without causing detonation. Compression is directly related to power and to thermodynamic efficiency (see engine tuning), so engines that require higher octane usually deliver more motive power and do more work for a given BTU or calorie of fuel. Engine power is a function of the fuel, as well as the engine design, and is related to octane rating of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure, or higher in the case of supercharged or turbocharged engines.
Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.
However, burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate (blow up), that reduces power and efficiency for the reasons stated above. Many modern car engines feature a knock sensor – a small piezoelectric microphone which detects knock, and then sends a signal to the engine control unit to retard the ignition timing. Retarding the ignition timing reduces the tendency to detonate, but also reduces power output and fuel efficiency.
Most fuel stations have two storage tanks (even those offering 3 or 4 octane levels), and you are given a mixture of the higher and lower octane fuel. Purchasing premium simply means more fuel from the higher octane tank; the detergents in the fuel are often the same.
The octane rating was developed by chemist Russell Marker at the Ethyl Corporation c1926. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.
..its important to note, that the engine designers, in most manuals, give a suggestion of which octane to burn. Its a common misconception that higher octane by itself gives more power..this is not true. Its effect is negligble when compared to a lower octane fuel in the same engine. The use of High octane fuels are as was discussed earlier..to stop pre-ignition, and "tune" the engine to get the highest compression possible without pre-ignition. Its that compression, and not the octane that creates more power. Its a reactive force, higher octane fuel allows for a higher compression motor to be more accurately tuned, allowing for a very controlled firing of the ignition system. Without the high compression, the higher octane, can of course help improve the firing reaction, but, its effects are limited.
Bottom line from my way of thinking..if you spend alot of time in the upper rpm range for your engine, then you could consider using higher octane fuel, not because it gives more horsepower (because it doesnt) but because of the more controlled aspect of the burn inside the cylinder, making the engine more controllable. But, I emphasize that the effect is negligable. If your only looking at octane to try and get a hp boost..your looking in the wrong place.
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2000 CBR929RR- Cams, Micron cf pipe and headers, Power commander 3 (custom mapped), heads, decked, ported, polished, zero gravity shield, Frame sliders, polished frame and swingarm, remote controlled red neons, Stainless Braided front and rear brake lines. RK 520 race chain and -1/0 Vortex sprockets, bitch pegs and rear seat removed, OEM rear seat cowl, Pirelli Diablo Rubber.
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