I know this has been discussed before but i need an answer. I have a 1991 Z28 and I have ran premium gas (91) in it for a while. And i was wondering if i should run 89 or 86 because i think i am wasting my money.

 

you only need to use above a 90 octane if u have a high compression engine. i know it is recommended for the LS1 but it is not for the average stock thirdgenner. i use 89 just because it makes me feel better but 91 isn't neccessary-save your money

 

i usually get 93, and i don't think i'm wasting money. in the manual (for my car at least), it said they recommend running premium, but you can run mid grade (89), but you'll accelerate slower.

i tried mid grade a few times, and i did notice my car seemed slower, so i stick with 93.

my friend's dad works for some company that makes gas (he's a chemical engineer), and he said that if the engine doesn't knock on 89, it's fine

 

If it's not pre-igniting on a lower octane, then you're wasting your money, yes.

 

i run premium fuel....

 

my tpi likes 89

 

IROCZ88x thats gotta suck leaving your car outside in the winter why don't you put that thing in the garauge

 

While you're correct, I think you're missing a huge part of the point.

True... if it doesn't cause pre-ignition, then you're wasting your money. BUT... with a TPI car, you'll never know whether it's causing pre ignition unless you hook up a scan tool. The computer well sense knock long before you hear it, and it'll pull out a bunch of timing until it's gone. If this is happening, you never hear the pinging, but you're losing power because the computer is pulling out timing. If you run 93 it won't have as much knock, so the computer won't pull out as much (if any) timing. More timing = more power.

My friend runs 87 or 89 in his 99 Super Sport camaro and no matter how much I try to explain it to him, he's convinced that because it's not pinging that he doesn't need 93.

 

I use 93 Octane

 

I believe my 87 Owners Manual recommends using Premium in the TPI cars... Considering TPI cars have a compression of 9.3:1 stock then I would say yes, use Premium... I know mine runs better with it...

John

 

Which is why I have a laptop w/ a couple logging softwares, and an AllScan1

Don't worry about me; I know what 85 octane from higher altitude areas does when I get down to 5k feet above sea level.