njvetteguy1

On the C6 general board, there is someone almost every day who posts an octane related question. There seem to be two camps who respond to every one. The first, and larger of the two, says "I paid $50k for this car, I'm not gonna go cheap on gas." The second group says "I don't notice any difference running 87 on the street, so why spend more?"

I'm speaking here about LS2/3 cars, not the LS7/9, which I understand take far less kindly to lower octanes. Also referring to totally factory cars with no aftermarket tune. Has anyone done a back to back dyno run with both types of gas and seen what the actual HP differences are? Is it possible to monitor the computer to see exactly how much it does when the engine is under load to combat knock. Or is running the engine up to redline while using low octane a bad idea?

I would be very interested to see just how much of a difference there is. Everyone just says the car dials back the timing for lower octane and you lose "a few" horses. Is a few 5? 25? 50?

KLLRVET

Who cares? People are silly. Over the course of 100000 miles, figuring that the car averages 16mpg(low), that Premium is 30cents/gallon higher than regular, you'd end up spending 1875.00 more. Roughly, .02 cents per mile.

0Brian@RPT

I have done something like this on my dyno. I had a customer dyno his 2010 C6 LS3 M6 and installed Kooks Headers. The initial pull was riddled with knock and up to 8 degrees of retard. This was from 2K to 6.5K rpm. Found out that it had 87 octane in the tank. You could actually hear it pinging and this was on a stock tune. So, running 87 octane in a Vette is not recommended and eventhough the knock sensors are pulling timing, damage is still being done. The Vette still gained 25 rwhp with no tune and tons of KR following the header upgrade. I am trying to get him back to dyno with 93 octane. He refilled with 93 octane and said the Vette was a lot better.

REVAK

I have reviewed my notations and those of others, on the LS engines the average is around 2 HP per degree of timing within the usable adjustment range on primarily stock engines. So , for instance if the knock sensors command a 5 degree retard, that's 10 HP.

njvetteguy1

Well you are basically taking the first argument, that you already spent $50k or more on the car, why care about 30 cents per gallon. $1875 isnt chump change though. I'm not here to make the argument either way, how people spend their money is up to them. If you were trying to spend money in the most prudent way possible, you wouldn't own a corvette to begin with!

My question is not "is it worth it" but "how much difference is there" regardless of cost.

njvetteguy1

This is the kind of info I am interested in, along with Brians info. In a totally stock car, how many degrees is the car going to retard the timing in a full throttle scenario under 87 octane? And also,under part throttle, moderate load scenarios, there will be absolutely no difference between the regular and premium, correct, because you wont be getting into the portion of the powerband where heavy timing advance is added?

REVAK

The only way to know for sure would be to data log your particular car. Things that impact how much timing you can run and how much knock retard you may get : Ambient air temp., altitude, load [uphill] , engine temp., incoming air temp., A/C on , etc. There are many variables so there isn't a set number on how much retard will occur. As far as part throttle is concerned, at 55% throttle you are into the wot timing tables. The highest timing advance does not occur at wot, it occurs during cruise and light load. Very generally speaking, in a colder climate, no ac , no steep grades, you may get away with 87 . In a hotter environment, more load, the pcm will switch to the 87 table to reduce knock, and this will reduce power. The 93 will reduce knock, allowing you to stay in the 93 table, thereby producing optimum performance.

0East Tx Muscle Cars

we have tuned many cars with 87 then changed to 93
on NA bolt on cars you will notice about 20-25 HP gain

on boosted higher hp cars we have tried 91 to 93 oct and have noticed over 20 rwhp gains on FI cars