Quote Originally Posted by keylay31 View Post
Can someone explain how adding or removing ethanol from gas affects a modern car engine?
Ethanol or any alcohol has a less violent ignition than gasoline. This means during the burn phase in an internal combustion engine it gives less power. Secondly, most modern fuel injected engines run in a open loop fuel stage looking at the oxygen sensor to get a clean burn. Ethanol and alcohols fool the oxygen sensor into thinking it is running lean due to the burn characteristics and run richer causing you to burn more fuel than using straight gasoline. If you are running these fuels in an older carb engines you will run lean unless you enrich the mixture to adjust for the alcohols.

Long story short you get less power and poorer fuel economy using oxygenated (alcohols) in fuel.