tcadman

I'm new to my 06 corvette. We got her in October and have only had time for a few drives and a couple of tanks of gas. I can't seem to find 93 octane so I've been using the 91 octane. She seems to be running just fine but I thought I'd ask about the difference and if we should be using some type of octane booster. We don't take her to the track, just on wonderful drives in the Sierra Nevada mountains and to the North Coast of Calif. Feedback would be great. This forum has been very helpful with a number of small issues. Thanks to all the great posts from everybody. I know there are newbies like myself who can truly benfit from all this knowledge. Thanks for your help, Tom, Lyn and Glory, Yes we did name her Glory with our vanity plate NRGLORY

Vette_DD

2006 owner's manual, page 5-5:

08vycpe

Your knock sensors and ECM will adjust the timing correctly and the car will run just fine on either 91 or 93. The higher octane gas burns slower and more evenly thus reducing the knock potential. The car then adjusts to allow more timing and slightly better performance.

barneyz06

one could further the question:

91 octane top tier vs 93 octane non top tier

or how about:

91 octane without any ethanol non top tier vs any of the above.

what to do, what to do??

Gearhead Jim

A couple of tankfulls of non-Top Tier aren't a big issue, but I would try to use Top Tier for the vast majority of my fuel.

We have a retired oil engineer here who says Top Tier really does make a difference over the long run.

haljensen

The factory tune is for 91 Octane (50 state). 93 won't do you any good without a tune. Aftermarket Octane enhancers won't do anything unless you have tuned the car for the increased Octane.

Yawlak80-86

I believe you are mistaken sir. It would seem you have it backwards. Octane boosters = waste of money. They don't work, and 93 octane will make a difference. On Vettes, factory programming is set up w/ 93 octane fuel as the base. It compensates for 91, making adjustments that cause our cars to run poorly. Heres how. There are two timing tables in our ECM's: A low octane and a high octane. At the 1st sign of a ping/detonation/pre ignition, the low octane timing table is utilized kicking down the timing considerably thus causing significant loss of power and economy. Even on top tier 91 octane, all C6's will ping with even slightly spirited driving, ( in Vegas and even in winter), then revert to the lower table. After the ping is not picked up by the ECM/knock sensors for a predetermined amount of time, the process will begin again starting with the high octane table and working its way down. The problem is especially bad with LS2's as they have too much timing combined with too high a compression ratio from the factory. They spend most of their time on the Low tables when using 91 and still ping.

I use HPT software and have monitored many cars on many fuels, (at least a dozen C6's), and have found that the discount/offbrand fuels are absolutely terrible! I wouldn't put that garbage in a lawnmower. The top tier fuels have better additives and are more consistent quality-wise. They are better, but still stink. Ethanol is not in any way bad for your engine, it's actually a good fuel. E85, (ethanol), is about a 110 octane fuel but burns less efficiently then gasoline therefore requiring much more of it to do the same job, (you need larger fuel lines, better pump, larger injectors, different programing-flex fuel vehicles are set up this way).

I have data logged my own vehicles in SoCal and found that the fuel there is terrible as well. I compensate for this by changing the cars spark curve on the high octane table to accomodate the crappy gas while making as much power as possible.

Moral of the story: Don't be penny-wise and dollar foolish. If an extra dollar or two per tank is going to hurt you, then you should not be driving a sports/performance car. Just because you can't hear your car ping does not mean it's not happening. If it's available to you, always use top tier 93. If not, use the highest octane available and don't drive it hard unless the car is properly tuned for less then 93. Top tier 91 > off-brand 93. On or near the west coast, I find the most performance-friendly fuel to be Sinclair 91 and the worst to be any octane fuel from Costco or Samsclub. In central and eastern US, Exxon/Mobil 93 does it for me.

When I go to the track, I run a blend of 100 octane race fuel w/ 91 octane pump gas making at least 95 octane so I can run adequate timing.

That's my rant! Hope it's useful to ya

barneyz06

what's your ratio of 100 to 91 octane. for as little as i drive this might work.

FNBADAZ06

I highlighted a specific comment you made above to support my following statement:

If all you do is part to light throttle cruising, 91 octane fuel is perfectly fine, and is all you'll find the majority of the time in that part of the Nation anyway. Stay with a quality tier one fuel to get the cleaning component introduced with their fuel detergent additives (and hopefully, a more consistent fuel product).

The benifit's of a quality higher octane fuel only really come into play if you start putting more of a demand on the engine or are interested in eeking out every last bit of horsepower out of the engine

Bottom line, if a data logger doesn't show any knock retard you don't need any higher octane fuel

Hoonose

12 gal on 100 octane + 4 of 91 = very close to 93 octane for a 16 gallon fill up.
This is what I used to do. I go on 'low fuel' with 2 gallons left.

JoesC5

I'm fortunate that I can purchase 94 octane Top tier 100% gasoline to run in my Z06. I run 91 octane 100% gasoline in my supercharged Mercedes and my two old Corvettes. Only thing that gets 87 octane E10 is my mower, but it gets drained each fall.

Fly'n Family

I live in the Rockies, where the highest octane available is 91. My car is well over 500whp with a tune based on 91 octane. No issues what so ever.

If I was a flatlander, I would run 93 as it's readily available. We really don't need it up here.

Gearhead Jim

The Owner Manual for a Z06 says the car is designed for 93 octane, but us lowly LS3 people have an Owner Manual saying the car is designed for 91. Is it possible that the LS2/LS3 you have logged showing reduced timing on 91, have some other issues? Or something else confusing the situation?

Looking for an education, not trying to start an argument...

Yawlak80-86

For the track, I have a more aggressive tune and use 50/50 of 100/91 which should give me a minimum of 95 octane. It works ok for me.


For the street, I just tuned my car to squeeze the most I can out of 91.

1/4 tank of 100 octane should give you near 93 octane.

Generally, use of straight 100 octane is a waste of money unless you have some serious engine work.

Yawlak80-86

I understand.
The first couple of times I ran into the issue, I checked the cars for any malfunctions/problems. I even did a Carbon Clean Motor Vac service on two of them figuring possible carbon build up could be the culprit, (although it wasn't, I highly recommend that service anyway). A vacuum leak or clogged/stuck closed injector would cause a high fuel trim reading, (which none of the cars had, all had fuel trims close to zero when stock), not to mention that the obd ll systems are very good at picking up malfunctions on their own. In short, no cars had any malfunctions. Once I modified/lowered the spark curves on the high octane tables, all the cars became a lot more 91 octane friendly.
The Ls2's, 3's, and 7's I've logged and tuned were all driven in real world conditions in various temps from 24 to 120 degrees ambient all around Vegas. Some had light mods done by me while others were completely stock. All had the stock tune when I got to them. If I'm doing engine performance work, I always do data logs before I touch a Vehicle to see if there is anything unsavory going on that should be addressed before I do any work. I've also had 1 c5 and 4 c6s which I logged and tuned extensively with all types of fuel from the east coast to Nevada. If I'm driving alone, I have my laptop connected.

The owners manuals are not gospel. LS3's have a slightly lower compression ratio than the 2's and 7's. They also have much better heads than the 2's,(perhaps the quench zone is relocated in the cylinders as a result - I'm not positive). Perhaps these are some of the reasons they say the ls3's are good w/ 91 but I can tell you with certainty, they are not, at least not in my neck of the woods. I can also tell you that I had no pinging issues on the east coast with premium top tier fuels, (except for Shell).

I think I may have completely over-killed your question but I hope this is helpful info.

04goatman

@ Flatlander

Gearhead Jim

Thanks.
Around here, all the Premium seems to be 93 but it also has ethanol.