Have a 95 z28. I used to run 93 for a while, but then switched to 89 just recently. It "seems"run better as far as comfort and driveability. Dont know why though, if anything I would think it would always run better on higher octane, but Ive filled up with 89 twice now and I think its doing better...strange? Its only got a K&N cold air intake, other than that its pretty much stock as far as I can tell (previous owner). I even run it aggressively and it runs better? I think I have my answer but I would like to get someone elses opinion on it. Thanks

 

You need to monitor the knock retard while driving.

 

Changed the spark plugs and wires...A world of difference!

 

This is a tough topic to explain but you will make more power on the higher octane fuel. It doesn't have anything to do with energy content, it has to do with volatility. In the combustion chamber, higher ocane fuel allows more timing with less chance of knock. This timing equates to more power. The whole purpose behind aluminum heads, reverse cooling and high octane fuel is to allow more advanced ignition timing and get rid of the extra heat generated by it.

The effect of lower octane rated fuel is knock. When the knock sensors pick up the unexpected vibration that ends up being interpreted as knock, the PCM pulls a lot of timing (retards the timing) and then adds it back slowly. This is clearly bad for performance.....

 

What is the elevation where you live? Higher altitudes do not require as high an octane fuel. Since they sell 93, it would appear you are near sea level, but it would help to know the elevation.

Just out of curiosity, what do you mean by "better as far as comfort"?

 

I had a sp wire that was shot and the plugs werent gapped properly, so it would drive very roughly. You could feel it from the engine to the exhasut, very rough idle. But replaced all of it and now runs like a champ except for a few other problems I have discussed in another thread. Thanks for all the insight and help everyone. I live in florida near the gulf so yes I live at sea level pretty much.

 

So you feel the better "comfort" was due to the lower octane, and not due to replacing bad wires and plugs? I don't understand.

 

No everything was fine once I changed the wires and plugs. The octane was never effecting it. I was grasping for straws because I didnt know what was going on until I contacted a master mechanic about it, who told me right away. But also was way too overpriced, so I did it with a friend instead. Sorry for the confusion