So I have had my 95 Z28 for about 2 months now and I love this car. The first few weeks I had it I was running 93 octane in it just because i didnt know what the previous owner had used and I wanted to run some good clean gas through it. After that and for the last say 5-6 weeks i have been running 87 just to save a few bucks. The car did not seem to have the same punch that it did when I first got it, figured I was just getting use to the car. Yesterday i was pretty low on gas and gas has come down by about .40 a gallon so I filled up with 93. After a few miles of driving the car felt awsome. It felt like it ran smoother and acellerated much quicker and smoother. I was once again blowing the tires of on the 1-2 and 2-3 shifts. needless to say im happy. After some research im reading that chevy recommends at least 91 octane. Is the 87 really that bad for the LT1 that it made my car feel noticably slower?
btw, its just a basic bolt on car with 111k miles on it if that makes a difference?

 

When you use 87 it may cause knock so your computer pulls timing which makes it lose performance.

 

The factory recommends running at least 91 octane like you discovered, so running the 87 for that length of time, considering the condition of the engine, temps, etc., it could cause some knock retard.

 

First things first, just because it's most expensive/higher octane does not mean it's cleaner or any better for your car than anything else.

The car will pull timing which may cause some loss in what you experienced. As you said, GM recommends at least 91.

Putting 93 in a chevy cavalier will not make it run any better, or any cleaner (as in clean your engine, who knows on emissions). The best gas for a car is what is recommended or what it is built for. Too much octane is not good.

 

Well, there are a few error in some of these posts.

All gas-station levels of gasoline have the same amount of energy per pound. That is not the value of premium over regular.

Octane refers only to resistance to knock. It is a test and gasoline actually has little to no octane in it. It is related to volatility of the fuel...and a bunch of other variable.

The difference in power has to be related to less timing advance allowed by the engine. One the PCM 'hears' knock through the sensor/module it pulls timing advance rapidly...to protect the engine...and adds it back slowly. Less timing advance equates to lower power.

Running gas station fuel with a higher octane than needed to minimize or eliminate timing retard will not hurt a thing. It won't add any power either.

Racing fuels are different and higher octane in those comes from different chemistry...the above doesn't fully apply to them.