Re: why wont it go FASTER!!!
Let's set the record straight.
Gasoline is a mixture of long and short chain hydrocarbons. These are carbon atoms linked together with hydrogen atoms attached to each carbon. When burned they produce carbon dioxide and water.
In reduced oxygen environments they produce carbon monoxide.
Years ago, the Society of Automotive Engineers set the knock resistance of N Octane (C8H18) to the arbitrary number of 100. All gasoline is measured against this standard. Various mixtures of hydrocarbons have more or less resistance to knocking (autoignition and detonation) and this is (relatively) independent of the carbon chain length. If interested, go to an organic chemistry book and read the flash points and ignition points of various hydrocarbons and alcohols.
All gasoline burns at essentially the same speed as evidenced by the fact that most engines use the same ignition timing advance. Engines with higher than about 9 to 1 compression ratio will operate at higher heat because air heats as it is compressed. The added heat (and possible glowing carbon deposits) will cause the low octane rated fuel to autoignite at a different point and time than at the sparkplug. When this happens two results occur: 1. because autoignition is earlier than at the plug, combustion pressures rise dramatically and cylinder heat is excessive. 2. When the flame fronts collide, they cause a hammering (ping or knock). The combination of knock and temperature melts the piston and blows away the melted aluminum, then shatters the rings.
The octane misconception occurs because in the 70s muscle cars used compression ratios of up to 13 to 1 and required at least 100 octane fuel. The faulty reasoning is: These engines were powerful so therefore the gas must be powerful as well. NOT TRUE!
Also, back then we used a compound called Tetra-ethyl lead to raise octane. This is a lead molecule with four ethyl chains attached. During combustion it released a lot of ethyl hydrocarbon chains which have a very high octane rating. Remind you of ethanol today? Oooh! let's not restart that argument! LOL Anyway, back in the early days (read Ford model "T" and model "A") high octane "Ethyl" gas did clean the engine a little better than regular and if there were a lot of carbon deposits in the combustion chamber, it would not autoignite as easily, so there was some slight advantage to using it. NOT so today.
If an engine has less than 9 to 1 compression ratio as most small outboards do, there is absolutely no advantage using a high octane rated fuel. In fact, all it does is to lighten your wallet. SO: Don't bother to buy 93 octane.
Now, back to timing advance. In order to extract the most power from the air/fuel mix and not harm the engine, it is necessary for it to burn approximately equal times before and after top dead center. Thus, as the engine is asked to speed up, we advance the timing of ignition until full advance is obtained near full throttle. Too much timing advance acts much like detonation so if we have low octane fuel, we retard the timing a bit to compensate. Power is reduced but the engine is not damaged.
In two cycle engines there are basically two types: Crossflow and loop charged. Because loop charged engines usually have a hemispherical combustion chamber with a "squish band" they DO increase the turbulence of the ignitied air/fuel mix and it DOES as a result burn faster. Thus: Loop charged engines usually have a timing advance of about 18 degrees versus the 30 degrees for crossflow. However, this is due to the engine design, not the gasoline. Again, even though the gas burns faster, ignition is not as advanced and these engines for the most part do not need or require higher than 87 octane rated gasoline.
