If I run 87 octane gas and then switch to 93 how long does it take the computer to adjust the timing for the 93 octane.

 

You would prob. notice the difference immediately but I don't know how long it would take to actually adjust. You never wanna run 87 though. I always do 93 and then 90 when I can't get 93.

 

There’s no “learning” involved. If the sensors detect knock the computer retards timing until the knock stops. Nothing more to it than that.

 

The EPA requires all cars to be capable of running 87 octane. Depending on where he lives, he may be able to run 85 octane gas with no decrease in performance/MPG due to KR. An engines' octane requirement is a moving target influenced by many factors. Altitude, barometric pressure, humidity, and ambient temperature are the atmospheric variables. 93 octane is required for worst case scenarios with a slight safety margin. Higher altitude, lower barometric pressure, higher humidity, and lower ambient temperatures allow lower octane fuel to be used and the right combination can result in lowering an engines' octane requirement below 85. In the winter in north Florida, my daughter runs 87 octane with no decrease in HP/MPG...why pay more for something you can't use??? In your location, I'd run 93 most of the year and 89 in Jan/Feb but in Denver, CO I'd already be on 87 now and looking to go to 85 as the temps drop even more.

 

Some members run only 87 and report no problems or pinging.

 

Less performance, computer will pull timing. I bought the car for performance, I run 93

 

I always use 93 with no ethonol.

 

 

Car will run on 87 even 85, but yes at a greatly reduced HP due to timing being pulled at an alarming rate.

 

87 pulls 15 degrees from the stock tune as I found while on a tuning trip to south Texas. The owner was told that it can run on 87 so he was trying to save money with the cheaper gas. I was trying to tune it and with the initial scans it showed the car had 15 degrees knock retard. When this happens the car reverts to the low octane table. Some tuners adjust the low octane table to more timing too but in some instances i have seen some lost souls actually tune a car and making the low octane table a dupe of the high octane table. Obviously this eliminates the ability to run 87 octane.

I think what you were saying was that in some plaaces like here in nose bleed land (high altitude) running 85 will not reduce performance or gas economy over 87 since the lower cylinder pressures allow the lower octane.

In case anyone read that to mean 87/85 isnt lower HP or mileage from 93, thats not true. The performance will be adversely affected by a 15 degree timing pull.

Back to Reuben's vette: There was a comical scene in Jogar80's driveway with a bunch of guys siphoning out all this 87 for 93 for me to then tune it. The car instantly ran the timing when it was filled with 93. Apparently its always checking to see if it can run the timing. It only takes a minute or two of driving to exhaust the gas in the lines going to the motor. There isnt any learning invloved.

My Hummer runs 85 with no knock retard even on 90 degree days. Its an alpha with only airflow mods done now for mileage. HPtuners tunes all GM trucks and the 5.3L runs from the factory here on 85. I think it will take a 4 degree advance and still run 85. Later when I supercharge it, it will be tuned to 91. My corvette runs 91 here with no timing pull while in NY I was at 93 octane and it wouldnt run 1 more degree anywhere in the timing table without having KR so the altitude variable is greater than most think.

 

I was thinking that but didnt want to type it. There are posers here to the Nth degree that would likely buy a vette with a 6cyl if it were available.

 

A dyno comparison with a new Z06 a few years back showed a 10-15 HP loss at peak HP comparing 89 to 93 octane. So the HP is not marked, and probably might only be detected on the race track.

 

The problem though is that the power loss is happening due to knock retard, and before knock retard can occur, there must be knock. I don't know about you, but saving a couple bucks at the pump is not worth having detonation in my hypereutectic piston engine... I really don't get some people's reasoning when it comes to buying a $50,000+ car and then trying to save pennies at the pump, but what I *really* don't get are the people who are willing to do that even if it can potentially harm their engine.

 

I run 87 all the time, I just don't get those people that swear the owners manual says premium only...It will NOT harm your engine in its stock configuration.....

As for timing, sure it goes to the low octane table, BUT only when needed to do so, it does not stay on that table if it is not needed. Heavy acceleration, loading etc will move the timing into the lower table...other than that, you will not notice the difference. If you have premium, it may go to this table at a lesser frequency. Changing from 87 to 93 will also have the same affect. There is no magic trigger to send the ECU to the lower table, just sensors reading the engine.

Enjoy all the blends of pump gas as YOU see fit...Just don't try to justify your decision with science when it comes to our stock C6's.....

 

It's not only about saving money. Higher octane gas takes more energy to produce, uses more natural resources, and has more environmental impact. There's nothing wrong with knowing what your engine needs and using no more...all part of "waste not want not". In Denver in the dead of winter, 85 octane would be all that's needed while south Texas in the summer needs every bit of 93 like Spin said above. A "smart" person may look at a person that runs 93 year round and say "I *really* don't get why people use 93 all the time when they don't need it".
It's just a matter of perspective really, run what you want but don't chastise people that are doing the smart thing. Having said that, my ZR-1 has had nothing but 93 octane its' whole life while my '95 Cadillac Concours would get 87 octane in the winter and a mix in the spring/fall. I would expect your supercharged car would be 93 octane year round but I bet you could get away with 89 octane and maybe even 87 octane in the dead of winter in NJ with no loss of HP/MPG due to KR. With your car having a centrifugal supercharger that doesn't build a lot of boost down low and the fact that knock is mostly a low RPM phenomenon, I think that would be a safe bet.

 

 

 

 

There is a knock learn factor that is computed and used to determine which table to get the timing from. Based on the amount of knock learn, the spark advance is interpolated from the two tables. Excessive and/or continuous knock adds to the knock learn factor. Running lower octane fuel will initially cause knock, however the PCM will gradually move to the low octane spark advance table until knock is no longer detected.

 

My comment wasn't directed at you; you obviously understand what the octane requirements of your engine are. If you look at my comment, it was directed at:

The premise behind that post is not that the Z06 doesn't need high octane under certain specific conditions; it is that it is OK to let the engine knock itself int 15HP of detonation induced knock retard because most people wouldn't know the difference... THAT I do not find very "smart".

For the record when I ran 22PSI of boost on my STI I had a switch that would allow it to run on wastegate pressure (8PSI) so I could get away with low octane and also get better fuel economy The mileage STILL sucked on that car though... 22MPG of cruise control highway only driving with no boost...