[JCunningham]

the cars tuned for E10 93 octane so 94 E10 will work just fine. better then 91 strait.

[JCunningham]

Originally Posted by 95 imp

The key to power is using the lowest octane possible without knocking.

My suggestion is get a tank of 91 and use a scan tool to see if the knock sensors like it.

If there is no knock showing under heavy load, you can mix some 87/89 in the tank to drop octane until knock starts showing up. Then add 91 back in to get rid of it.

If it is knocking on 91, add 94 until the sensors say knock is reliably gone.

The octane requirements will change based on weather (IAT and humidity) and age (carbon deposits raising comp ratio and hot spots).


99% of the time, you actually lose power (and create more emissions) with higher octane fuel because it just isn't burning completely and going out the exhaust valve.

My gen 2 lt1 (@ 10.5/1) does just fine on a tank of 20 gal 89 and 5 gal of 91 in the winter. Summer time needs more 91.

you will have to reset the computer each time it goes into the low octane table as its not instant going back into the high octane table.

[mdhopt36]

I would think that the 91 straight would be just a tad rich---needs more O2 to burn than E10. If the car is set up to use E10, use it.

But I like the idea if car can be tuned for straight 91 and was commonly available, I would certainly use that. Heck of a lot less issues with straight gasoline storage wise, etc.

[BradfordCamaro]

94 all day, everyday.


The 91 will be fine but with 94 available why not use it. The *up to 10% ethanol means nothing in our cars as stated in this thread.


I have posed this question myself. Always go with the higher octane. And you get points and up to .8 cents off.

[mdhopt36]

I noticed yesterday our Shell here is E10- 93 octane. (all I use)

[95 imp]

Originally Posted by JCunningham

you will have to reset the computer each time it goes into the low octane table as its not instant going back into the high octane table.

Not quite how that system works....

Every time you start the vehicle it goes to the high octane map. If it picks up knock, you are correct that it drops to the low tables and slowly climbs up to find the right one to work with the current fuel.

Turn the car off and turn it back on, this process starts all over again.

[BlueinTN]

I always thought the opposite of what you say how can we check this out?

[DorkMissile]

Asked my tuner if I should use 91E10 or 92E0 (what we have locally) and he said that locally the 91E10 is the "harder to detonate fuel" we have available locally.

No reason to fear the Ethanol content in the fuel, every system on the car is meant to work with it.

FYI - Minnesota is now mandating 15% minimum E content in all unleaded fuel. Great for my Camaro, bad for my 88 Monte Carlo, Snowmobile & Motorcycle

[TJay74]

Originally Posted by JCunningham

you will have to reset the computer each time it goes into the low octane table as its not instant going back into the high octane table.

No you dont have to reset and yes it does instantly go back up into the High Octane table. Once the last occurance of detonation happens the decay cycle begins, once the decay cycle clears the ECM moves back into the H.O. table.

It literally takes less than a couple of seconds for the whole process to happen.

[TJay74]

Originally Posted by DrkPhx

From the owners manual:

For the LTG 2.0L L4 turbo or the
LT1 6.2L V8 engines, premium
unleaded gasoline meeting ASTM
specification D4814 with a posted
octane rating of 93 is highly
recommended for best performance
and fuel economy. Unleaded
gasoline with an octane rated as low
as 87 can be used. Using unleaded
gasoline rated below 93 octane,
however, will lead to reduced
acceleration and fuel economy.
If knocking occurs, use a gasoline
rated at 93 octane as soon as
possible, otherwise, the engine
could be damaged. If heavy
knocking is heard when using
gasoline with a 93 octane rating, the
engine needs service.

The 2016 manual said 91 octane, GM revised the manual later in the year and then the 2017 manual came out with the 93 requirement.

Basically it comes down to this, run the highest grade you have in your area. We only have 91 but we have E85 so I can blend my own. if you have 92, 93, 91 E10, 93 E10 run it.

[Canadian ZL1]

Originally Posted by BradfordCamaro

94 all day, everyday.


The 91 will be fine but with 94 available why not use it. The *up to 10% ethanol means nothing in our cars as stated in this thread.


I have posed this question myself. Always go with the higher octane. And you get points and up to .8 cents off.

I concur...I run the 94 all day long and would not consider the 91 Shell. As a back up I can run the Esso 93. I live in a area where I have the choice.

[Clearly_Canadian]

Chevron 94 is all I have been using. Like spartan mentioned. Gas on the west coast is garbage. Why risk it is save a few cents?

[mdhopt36]

E15 is also bad for chainsaws, lawnmowers, and outboards. And won't store worth a shit any better than E10, either.
I've been fiddling with engines for over 50 years.
Run either straight gas, or straight ethanol. But mixtures have got too much headaches to be truly practical.
Too bad it's all we have out there, except for a few stations or stores that offer non-ethanol gas- and they are almost as scarce as a T-rex.

[VinnAY]

The only thing I saw from 87-91-93 (all e-10 I believe) was in my wallet. MPG is a non-factor and the car was otherwise undectable from the driver seat what octane it was running with.