JakeRobb

Sometimes people get better numbers on premium fuel than on regular, even with no knock when using regular. In general, I suspect that this is because some gas stations put more/better detergents in their premium fuel, and it cleans out the injectors / fuel filter / etc.

Assuming a perfectly clean fuel system and no knock in either case, performance should be identical between fuels of any octane rating, unless the fuel's octane rating is so high that it simply doesn't combust when the spark plug fires.

2010_5thgen

ok, so if using higher octane fuel doesnt do anything.......why is there higher octane than the normal needed ?

blown94

Running higher octane fuel is usually to control detonation on high compression/boosted engines. It allows you to run MORE timing without detonating. Like I stated in a previous post, higher octane fuels are more resistant to burning under compression alone, without spark. If you want to argue about seeing 5hp more with higher octane fuel, I suggest you figure out why some cars run on 87 and some on 93.

2010_5thgen

your right. i have no clue about tuning an engine. thats why i have my performance shop do the work for me. and the reason i ask these things is to learn.

JakeRobb

Because you can modify the engine such that it would require it. Such modifications are those that change timing, increase compression, increase combustion chamber temperature, or add manifold pressure (boost). All of those things increase the chances of predetonation (aka knock), which is bad. Higher octane fuel is (by definition) more resistant to predetonation, so if you make those changes, you use higher octane fuel.

If you put 87 octane in your Camaro, you'll get some knock. The knock sensors will detect it and put the PCM in a different mode which is programmed for 87 octane. As I understand it, the programming differences are mostly in the spark timing, and they'll cost you some power and efficiency.

If you put 100 octane in your Camaro, it'll run in regular 91 octane mode, and you won't get any knock. The knock sensors will therefore not detect any knock, and you won't go into low-octane mode. End result: you paid extra for the fuel and it didn't really get you anything.

Now, GM wants to get the most power and efficiency they can out of the engine (within reason), so the tune pushes the limit of what 91 octane (the highest widely available fuel) can handle. Once in a while, you'll get some knock, especially on hot days when you're pushing the car hard. Adding some octane booster or some high octane fuel to the mix will reduce the odds of knock in that situation.

If you're on a dyno doing a max power pull, there's nothing wrong with adding some high octane stuff just for safety. Having said that, if you're on the dyno in your street car, and just getting numbers for bragging rights, I'd suggest that using any fuel other than what you'll use on the street is just going to lead you to potentially incorrect results. Get some 92- or 93-octane pump gas and call it good.

2010_5thgen

well thank you for the explenation. thats what i was looking for. so basically if i run any higher octane, i need to have it tuned to run with that combination of fuel(93 and 110), if i want to run higher octane? and there is no harm in the motor if i get it tuned to run like this?

sharpe

Man, read the replies in this thread. C'mon.

Why would you want to add 110 fuel to your car before having it tuned? Yes, it could harm the performance of the car if its tuned to run like that. This thread tells you why.

JakeRobb

If you run higher octane, you need to have it tuned to get any benefit from that higher octane. You can run it and be entirely free from harm, although if you go significantly higher than what you're tuned for, it'll cost you power simply because of the higher-octane fuel's extra and unnecessary resistance to combustion.

If you get your car tuned with more spark advance to take advantage of higher octane fuel, you'll be putting more stress on the engine (especially the pistons, which are arguably one of the LS3's weak points), and you wouldn't be getting much out of it. The tune would require that you always use that higher-octane mix of fuel, and you'd have to be very careful to always create a mixture with at least that octane level, or you'll create knock. You do have knock sensors that will dial back to low-octane mode when knock is detected, but the tuning changes you're talking about would mean that the knock would be even more destructive. I don't think you should take that chance on a car you want to drive a lot, and the bang for the buck is pretty dismal anyway.

So, no, I wouldn't say there's no harm. There's a large chance for harm. It's entirely possible that you could go years and be fine, but in all honesty, if you're looking for more power, there's plenty to be had on 91 octane and there are far better ways to spend your money.

2010_5thgen

oh really? thanks bud. about a day late and a dollar short.

santiagocabral

Just though I would add my two cents in to the octane question. this is a copy blog I put in an other post.

I have owned my 2010 camaro since the first week of June 2009. I have had many issues with gas/octane. I have tried both ratings and found that the 91 and up is far better when it comes to mpg and performance. But I have also had more issues with the brand of gas then I have with the different octane rating. I have talked with other corVette and camaro owners about this to see if they have notice the same, they have. So far I have spent 12 months resurching this issue and I have found that Texaco gas is far far more consistant with reguards to mpg at the 91 rating. I have tried 94 at off the wall brands gas stations and they all failed terribly. My mpg fell down to 14 city and 17 hw. I was pissed, mainly because I filled the tank with this cheep gas, and it was all 91 and up. I have found the Chevron and sometime Shell are not bad but I will get one bad tank out of 3. So far with Texaco I have not got one bad tank for six month now. I have covered Texas, New Mexico and Ariz with Texaco gas, its all good. At first I went back to the dealership and complained about the mpg, I had them do a complete Diagnostic and found nothing wrong. that was when the shop supervisor mention the issue that other corvette owners have had the same issues for years. I beleive that some of this stations are putting the 87 in the 91 tanks, also there is just to much water and junk in the off brand gas even at the 94.
I am a happy camper now, no matter where I go I alway fill up with Texaco gas. I am getting 27 to 29 highway most of the time on flat terrain and no less then 25. In the city I get no less then 19mpg, thats with some hotdogging too. half the time I will get 21 in the city.

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JakeRobb

Octane rating is not a percentage. I think that when you say Taxco, you're referring to Texaco. Is that right?

You're correct that some gas stations sell gas that is not actually the octane rating they say it is. If you use any such bad gas, your car's performance will suffer. If it's really bad, you can damage the engine. Adding octane booster might help in some of these situations.

There's no Texaco around here. I've had great luck (on my 2002) with Speedway, BP, Shell, Sunoco, Marathon, and Mobil gas. I avoid Admiral gas. Citgo is hit-or-miss, so I avoid it unless I have no other option and I'm desperate.

I get the impression that the southwestern region of the U.S. has more issues with gas quality than we do here in the midwest. I'm not sure why.

2010_5thgen

my buddy used to own a gas station and i think they had shell gas. they told me bp was junk, but speedway was ok. i use sunoco when i am in the area of the 1 station they have around me. other than that i use citgo or speedway.

santiagocabral

OOPs sorry about that, I use percents in my job all the time and I had it on the brain. and yes I did mean Texaco. I am so use to typing out "Texas" I don't know what my brain was thinking at the time.
Question; out of all those gas stations you metions which one or two would you say was the most consistent in regards to quality/mpg/performance. I do some traveling and if there are noTexacos then I need something that is equal too.

on some of the bad tanks I got in the past I tried all the best octane boosters and nothing helped, bad gas is bad gas and nothing will make into good gas.

JakeRobb

The ones I said I like are all equally consistent -- that is to say that I have never had a problem with any of them. I really couldn't pick.

I am under the impression that Shell gas is better than most, but not in terms of mpg/performance. It has more/better detergents and other additives than most other fuels and will (over time) clean up carbon deposits left behind from previous bad gas. Again, this is just my impression, and it's not based in any sort of science or relevant experience.

santiagocabral

well that is good to know, I hate putting bad gas in my camaro. I have not used octane booster in years, those were my high school days. I just go get the 120 for my 69 camaro, Nova and sand rails when I go to the the track or out to tare up the country side. I have built all of my cars that I drive over the years, I have not bought a new car since 1979, my chevy van. but when I saw the new camaro I had to get it.