Shell 89 octane
Race Director
Joined: Sep 2011
Posts: 10,742
Likes: 211
From: Marana, Arizona
This is an age old question that has come up a many times.
Yesterday - we had occasion to dyno tune an '08 C6 (LS3) with an Edelbrock supercharger that had been installed and tuned in Indiana. The car was tuned for 93 octane....we have only 91 octane here in Arizona.
The car detonated with anything more than about 8-9 degrees of timing. We tried everything to figure out why. We pulled out a boroscope and took a look at the tops of the pistons. They were all cratered and looked very similar to the surface of the moon. The owner admitted that he had been running 87 octane from time to time. Also the installing shop had de-sensitized the knock sensors to the point of them not working at all.
This car should have been able to run 12-14 degrees of advance with no issue, and would not without a lot of detonation. Bottom line is we de-tuned the car, the owner is going to try a couple of cans of Sea-Foam to break up the carbon on top of the pistons. We'll re-check the car after he does the Sea-Foam, and runs a couple of tankfuls of 91 Chevron through it. I have my doubts, it looked like damage to me.....
So to answer the question - can the car run lower than recommended octane? Yes - if the timing is retarded. The knock sensors should be able to handle it - but the long term affect is not desireable. You will get less performance due to the retarded timing, and less fuel mileage as well. All in the interest of saving about twenty cents per gallon times maybe 15 gallons. That's three dollars for a 15 gallon tank. To me - not worth it.
I try to run the fuel that is recommended, and that is at least 91 octane. Your car - your choice.
Yesterday - we had occasion to dyno tune an '08 C6 (LS3) with an Edelbrock supercharger that had been installed and tuned in Indiana. The car was tuned for 93 octane....we have only 91 octane here in Arizona.
The car detonated with anything more than about 8-9 degrees of timing. We tried everything to figure out why. We pulled out a boroscope and took a look at the tops of the pistons. They were all cratered and looked very similar to the surface of the moon. The owner admitted that he had been running 87 octane from time to time. Also the installing shop had de-sensitized the knock sensors to the point of them not working at all.
This car should have been able to run 12-14 degrees of advance with no issue, and would not without a lot of detonation. Bottom line is we de-tuned the car, the owner is going to try a couple of cans of Sea-Foam to break up the carbon on top of the pistons. We'll re-check the car after he does the Sea-Foam, and runs a couple of tankfuls of 91 Chevron through it. I have my doubts, it looked like damage to me.....
So to answer the question - can the car run lower than recommended octane? Yes - if the timing is retarded. The knock sensors should be able to handle it - but the long term affect is not desireable. You will get less performance due to the retarded timing, and less fuel mileage as well. All in the interest of saving about twenty cents per gallon times maybe 15 gallons. That's three dollars for a 15 gallon tank. To me - not worth it.
I try to run the fuel that is recommended, and that is at least 91 octane. Your car - your choice.
!!!
Melting Slicks
Joined: Dec 2003
Posts: 2,857
Likes: 2
From: pawleys island sc
What's "old" got to do with it?
if you don't know or understand how your car's tuneing is setup with regaurd to fuel octane, assume that the guys that built you car know just a little more about the car than you do and then USE THE GAS THEY DESIGNED THE CAR TO RUN ON. But, then, it IS your car, so use anything that makes you happy.
if you don't know or understand how your car's tuneing is setup with regaurd to fuel octane, assume that the guys that built you car know just a little more about the car than you do and then USE THE GAS THEY DESIGNED THE CAR TO RUN ON. But, then, it IS your car, so use anything that makes you happy.
