Originally Posted by Donnie144
This came straight from Tohatsu they didnít recommend me running anything other then reg unleaded in my TLDIís because of the extra ethanol used in the supper to up the octane and decrease emissions. Their comment was that the seals in the outboard are good to about 10% ethanol anything greater will start to dry out and crack the seals in the fuel system.
There are a number of different ways to up the octane rating of gas. Ethanol is one (ignites at a higher temp than pure gas); however, it's primary purpose for being in gas in the US is as an oxygenator. Oxygenated fuels burn more completely, reducing visible pollution.
A while back, the gas companies had the US gov't require MTBE as an oxygenator, which raised gas prices by about 15 cents a gallon for the added production costs. When they were about to be sued for MTBE polluting groundwater, they agreed to change to ethanol, but it would cost about 15 cents a gallon to stop putting MTBE in, and a bit more to start blending ethanol. All the while, the big oil companies were turning record profits. Go figure.
Higher octane fuels in most engines will not release more energy than lower octane fuels. As someone said above, they are harder to ignite, so have less of a tendency to detonate (pinging, knocking, dieseling, etc.) Most high performance engines will require it due to higher compression ratios. Engines that run very lean may also, due to higher heat levels. Normal engines may see a very slight change in power output due to changes in detonation timing, but it generally will not be large enough to detect without dyno'ing the engine.
The opposite, however, is very bad. Running low octane fuel in an engine designed for high octane will cause pre-ignition, which will prematurely wear valves, pistons, rods; pretty much all moving parts in the motor.