General octane question

pretty much yeah, otherwise you can always buy some octane booster.

I think 91 is the highest that most of them require. If you use lower octane, the computer will retard the spark timing to compensate, reducing performance and/or fuel economy. I don't imagine there would be any other long-term consequences..

Most domestic brands today require only 87 octane fuel. It is generally only those engine that develop their torque at higher RPM's and must be wound up over 5,000 RPM's to gain their HP, like those found in foreign cars, that NEED high octane fuel. Engines that develop their torque ar lower RPM's, like most domestic engines, use 87 octane. My 2003 260 HP Mustang GT, for instance, requires only 87 octane fuel

mike hunt

Robert Hancock wrote:

No it has to do with compression not rpms. Supercharged 3800 is a low end torque motor but it needs higher octane fuel. Older muscle cars used to use 100 octane or better and they werent high reving engines. If your compression on a naturally aspirated engine is 9.5:1 or less you should only need 87 octane. Now some cams can effect your actual compression so keep that in mind when building a motor. Also you may not have engine ping in the summer but when winter comes along with the denser air you might notice ping (on older engines). What people dont understand is they have low compression engines and they think using a higher octane gas that it is somehow cleaner which it isnt or makes more power when it does not. Those people just throw their money away.

Also in reality a higher revving motor wouldnt WANT to use higher octane gas, since its slower burning.

If you're in a state that supports corn subsidies (Ethanol in gas), beware of higher octane fuel. Our '91 Jimmy had a fuel delivery component fail every 12 months because Ethanol was damaging the part.

We were told that higher octane fuel has a higher concentration of Ethanol in it.

By Federal law any pump that dispenses gasoline with alcohol added must post that fact in plain view on the pump. You will see an easy to read sticker which clearly states: Contains 10% ethanol.

On cross country trips sometimes thats all that is available in certain areas when you need gas. Since I only use it on rare occasions I can't say I've have any mechanical problems as a result, either on carubureted engines or injected engines. What I did notice on both vehicles is the gas mileage dropped slightly when using it. I attribute this to the fact that the ideal fuel / air ratio to burn alcohol requires approximately twice as much fuel as the gasoline to air ratio.

We were told that higher octane fuel has a higher concentration of Ethanol in it.