1995 Firebird Formula, stock except K/N filter and cat back exhaust. Daily driver, never raced or really driven hard anymore, 113000 miles.
There is a gas station here in Gainesville that now sells ethanol free 90 octane. I usually run 93 with the up to 10% ethanol and was wondering is it better to run pure gas and can an LT1 run 90 octane, I think the manual says it has to be 91 octane. Anyone have any thoughts?

 

The manual says to run 91 octane for maximum performance. It also indicates that you can run as low as 87 without engine damage, but you will lose performance. The knock sensor will cause the PCM to pull timing.

The octane rating determines if you will encounter spark knock. Doesn't matter if it's pure gasoline or an ethanol blend. 91 is 91. You may get better mileage without the alcohol.

 

Thanks for the answer. I dont really mind my mileage, at 70-ish in 6th gear I still get 25 or mpg. I just am afraid the ethanol is doing bad things to the rubber fuel lines and other parts. Maybe I worry too much.

 

I just recently read the manual and it states that I should run 91 or higher. The car has 48,000 miles and the guy who owned it for about 14 years before me said he ran 87 in it, so that's what I've been doing. Will I notice a difference with 93 like we have here? I didn't know if the car was maybe used to running 87 now or something...

 

Read the manual again. It says for the V8 engine:

If you switch from 87 to 91, you should notice improved power. Depends where you live. The higher the altitude where you live, the lower octane your engine needs. But you didn't show your location in your profile, so I can't tell. And you provide no info about your vehicle - year, engine, etc., but I assumed you have a V8 engine.

You need to add a "signature" with basic info about your car - year, model, engine, trans and any major mods. The more info you provide, the more accurate help we can give you.

 

Sounds good to me! I'll add a sig, but it's a bone stock 1995 Z28. I live in Pennsylvania and we have 93 octane as our premium here. I just wondered if the car could've gotten used to the lower octane gas somehow, but I guess not. I'll find out on the next fill up! I never noticed any knock or pinging so I guess the pcm does it's job well, and it never seems to hesitate. Sometimes a bit sluggish on the highway, but that's all!

 

There is a flag in the PCM for extended use of low octane fuel. But once you start using the correct fuel, it will clear.

 

Cool! I don't mind spending an extra $3 for better performance. Thanks!