[bonzoesc]

> In some places, the high octane gasoline does not have ethanol in it but some cars do not run as well on high octane gas because the gasoline does not ignite at the most efficient time for the engine.

I don't believe this is the case. Gasoline engines with higher compression need the higher octane fuel because it won't ignite at the temperature and pressure in the cylinder prior to the spark plug firing. Once the plug fires, the temperature and pressure are right for gasoline of any octane level within reason to combust.

There's no downside to running high-octane racing gasoline through a low-compression engine like the Atkinson-cycle engine in the Prius, but no benefit either. Other engines, like the 5.0 V8 in the Mustang GT, have different performance ratings for different grades of fuel. Still other engines, like the 2.0T I4 in the Volkswagen GTI, require high octane fuels for the extra compression they run.

[dmckeon]

If the engine has adaptive ignition (retards spark in response to pinging/detonation) then using lower octane fuel in a higher-compression engine may not result in engine damage - just less power.

OTOH, using higher octane than the manual / engine specs call for is just a waste of money for no extra power - but is not damaging to the engine.

One of the less-noticed issues with ethanol as a fuel is that it contains/provides ~33% less energy than gasoline[1] - so saving n% per gallon at the pump may cost you n% in mileage down the road. [1] http://www.eia.gov/tools/faqs/faq.cfm?id=27&t=4

More stops for gas might benefit fuel vendors by providing them more opportunities to sell you higher-profit impulse or convenience purchases over the counter.

[lostlogin]

It's not as bad as damage from pinging, but fuel lines may still end up perishing - I have never seen this but have read of it