Holy hidden HP!

[mcshocks]

So yesterday my tank was on E, stopped at a gas station and they were out of mid grade 89, so I threw in 91 instead. Well today I get out on the highway stomp on her, holy #@it felt like I slapped on 30whp. Are these engines known to detonate on the stock tune on 89 octane? Blew my mind so I did several more wot runs and I was , needless to say I think the pcm must have been seeing KR before and now with the 91 it's not there and the car is thanking me and giving me my ignition timing. I was kinda , but out of anything I have done this is the best the car has ever felt and it's in the upper 80's outside today and pretty damn humid.

[hemiunderglass]

I'm sure that's a complete coincidence. The manual recommends 89 octane because there is no difference in power from 91. So, why pay more for no gain?

[formerice]

That's interesting, cause mine ran fine on 89 even with a 93 SC Tune, never ever pinged. I do normally run 93, gas mileage seems better.

[CoolVanilla]

Right, octane is not a rating of potential power; 87 will burn with just as much energy release as 93. Octane defines how controlled the burn will be. In very high compression engines, a higher octane fuel will help avoid detonation (preignition) and therefore ping/knock, and therefore the knock sensor wont trigger, and therefore the computer wont pull timing, and therefore rob power...

Run the lowest octane you can without knocking. You'll run more efficiently and save money without giving up any power what so ever.

[mcshocks]

Right, octane is not a rating of potential power; 87 will burn with just as much energy release as 93. Octane defines how controlled the burn will be. In very high compression engines, a higher octane fuel will help avoid detonation (preignition) and therefore ping/knock, and therefore the knock sensor wont trigger, and therefore the computer wont pull timing, and therefore rob power...

Run the lowest octane you can without knocking. You'll run more efficiently and save money without giving up any power what so ever.

Exactly Cool Vanilla, that is why I never ran the 91 octane in the car. I have never scanned the car though to see where it sits, I threw it in just because they had no more mid-grade 89 left, I figured it would hurt performance (as it's harder to burn and would probably run rich) but I guess I was wrong. Need to get a scanner but I am holding out for a tuner here (which will have the scanner), at that point then I can try and verify my theory.

[BoiseHemi]

I use 93 because the quality of that particular fuel is good around here and also higher octance drops the chance of detonation if I open up the bottle. Later

[ThreeHundredSee]

OK, forgive this question, but I am a noob. So our car requires 89 Octane? I have been putting in 87 the last few weeks...Putting 89 or higher, will that increase my MPG? Thanks.

[ceemego]

I have run 94 in my 5.7L, way more get up and go!

[Arch Stanton]

OK, forgive this question, but I am a noob. So our car requires 89 Octane? I have been putting in 87 the last few weeks...Putting 89 or higher, will that increase my MPG? Thanks.

No, it won't increase your gas mileage. Your car should run fine on 87, but the computer may retard the timing a bit to keep it from pinging (premature detonation) which will, in turn, hurt performance a bit. You're best off to stick with the recommended 89 IMO.

[Carfinish]

I am going to agree with CV and others on the octane power thing....but my car seems to love octane and when I run 91 or better....she definitely pulls harder....and when I add octane boost, she likes it even more....that's the SOP factor and my track times kind of back it up even in bad DA...go figure...I can't explain it, but I gotta get a dash hawk or something else to see where the timing is on WOT...and correct I do not see any significant diff in mileage...if only I could stay off the throttle for like a week or so to see what happens

[ThreeHundredSee]

No, it won't increase your gas mileage. Your car should run fine on 87, but the computer may retard the timing a bit to keep it from pinging (premature detonation) which will, in turn, hurt performance a bit. You're best off to stick with the recommended 89 IMO.

Thanks. Will do.

[Husker]

I have run 94 in my 5.7L, way more get up and go!

Can you help me understand what you mean? All the higher octane fuel does is control the burn better, it has zero to do with actual HP. On the 5.7, it is pretty much a waste of money and I believe it's not reccommended to run anything about 89

[Super T]

I tossed 93 in my RT a few times just for grins, made no discernable difference. 89 worked just fine.

[RTracer]

91 made my car much peppier...of course I loaded the SC tune before i upped my octane

[Intimidator]

I threw it in just because they had no more mid-grade 89 left

This didn't happen to be one of those stations where the 91 is labeled non-oxygenated is it? I could see that making a huge difference. I know for a fact that stuff is night and day in my motorcycle. Our gas here really sucks with it's 10% ethanol and oxygenation.