So is it possible that computer will advance timing until it senses knock on newer cars? Seems this engine has 11.8 as it's the same drivetrain from the LS series, just minus direct injection.
Not sure it was the main reason, but there was a death there, can't recall all of the details though. When we were racing 2 strokes we used to buy race fuel there.
I'm not certain it goes that way, I suspect it is more that there is a target advance, it will maintain it if it isn't knocking.
At 91 it may not be running at full potential then?
No. The ECM operates within a set parameter and only adjusts the timing when the knock sensors trigger, it doesn't add timing until they ping and then back off.
You likely just got some really good quality fuel. I have had flukes like this before, no other change besides the brand of gas and got really good mileage and then the next tank is back to what it was. Fuel quality varies wildly from station to station, and that can change between tank fills (referring to the station's tank).
How many miles are on your engine? Carbon build up and worn parts can cause a decrease in performance that higher octane (or more likely formulation additives) may remedy. If you have some carbon build up in your combustion chambers, the engine may be knocking and the ecm is pulling timing to compensate. The higher octane fuel reduced the point at which the knock occurs, allowing the ecm to run the timing where it is supposed to be. I would suggest a cleaning product, like Seafoam or CRC 1-Tank Renew. I put some CRC in my 2002 2500HD (6.0 liter LS-series) on a road trip hauling a 24-foot race trailer. The first tank was normal, the second tank I picked up 2 mpgs while towing an 8500 lbs load, went from 6 to 8.
As was pointed out already, octane is only about controlling detonation. If you prefer to hear it from the horse's mouth-
http://www.exxon.com/octane-rating
"The recommended octane level for most vehicles is usually octane 87, but be sure to check your owner’s manual. Some car models have high-compression engines, which are designed to utilize octane levels of 89, 91 or higher. Ordinarily, your vehicle won’t benefit from using an octane higher than your owner's manual recommends. But if your engine knocks or pings at the recommended octane level, you may need a higher octane gasoline to prevent knocking."
How many miles are on your engine? Carbon build up and worn parts can cause a decrease in performance that higher octane (or more likely formulation additives) may remedy. If you have some carbon build up in your combustion chambers, the engine may be knocking and the ecm is pulling timing to compensate. The higher octane fuel reduced the point at which the knock occurs, allowing the ecm to run the timing where it is supposed to be.
It was Shell gas. I use Seafoam regularly in all my vehicles and BG 44K at oil change and addition to their ethanol dryer product, whatever it's name is. This one has 70K on it.
I believe everyone and I understand what is said, but something caused it to run better and that's the only variable I see. Still wished we could get some 93 here though.
Several things have happened in that time. I know that at some point there were only a few Texas counties (Houston, Dallas, etc.) requiring ethanol or oxygenated fuels but maybe they've changed. I know that the previous poster saying you can't find non-E10 fuel is true in the panhandle, exactly where one would think that you could find real gas since there are oil wells and tank batteries everyfreakingwhere!
Also the .gov has created an environment that basically forces them to quit refining all the different octane grades. Most of them, key word being most, are only doing 84 and 91 gas. How do they get 87 and 89? They blend the appropriate amount of ethanol or mix the two together to get the grade they need in the case of pure gas.
I agree with 4play, you likely got a good batch of REAL gas that was probably from a local refinery there in Texas.
I agree, I would prefer 93 for my boosted cars.
OK, so if I can get better performance from good quality gas, then who makes the best quality gas? Anyone know?
Going to be hard to distinguish, most of the retailers are drinking from the same tap...
Your biggest improvement will be running non-ethanol, in my F150 I see a consistent 2-3 MPG difference.
