I am tired of people who think high octane fuel will increase horsepower. You are just wasting your money if you use it in a non-performance engine.

So I wrote this fairly short explanation:


Octane is a rating of a fuel's ignition point (as in temperature at which it burns). The higher the rating, the higher the ignition point of the fuel.

If you put 87 octane in a Cobalt SS/Supercharged, for example; there is a high possibility for preignition or spark knock/misfire because the higher compression in the engine heats up the 87 octane to its ignition point before the piston reaches TDC (Top Dead Center) and therefore prematurely ignites causing spark knock/misfire.

If you run 93 octane in a Cobalt 2.2L, the 93 octane will not ignite when the engine is at TDC. Instead, it will ignite too late due to the lower compression in the engine than the 2.0L Supercharged, and therefore will not build up enough heat to ignite the fuel as efficiently as if 87 octane were used. With the 93 octane in a low compression engine such as the 2.2L, the fuel may even ignite after TDC which would actually rob you of power due to the fact that you are not able to use the full stroke of the piston to create power. This is also considered a misfire.

In both of these cases, the PCM/ECM will receive a message from the knock sensor telling it that there is a misfire in the engine. The PCM/ECM will then adjust the timing (spark and fuel) accordingly to effectively get rid of the misfire, the PCM/ECM will then start to slowly adjust the timing back to where it was before the misfire and when it starts to get the misfire again, it will adjust to get rid of it and repeat this several times until it eventually learns a timing setting that is most efficient without getting a misfire. But the engine will not be running as efficiently or with as much power as if it were run on its reccommended fuel. The PCM/ECM does not have unlimited adjustment on the timing of the engine, it will eventually run out of adjustment and you will be stuck with a misfire and a CEL/MIL.

In short, always run the recommended fuel unless you have modified the engine with forced induction or raised the compression of the engine.

 

im pretty sure the SS/SC runs on regular old 87 octane... which is one reason i got it instead of the SRT4 which requires premium unleaded. correct me if im wrong... but i do have a SS/SC, and i run 87 and it runs very strong. there is no need to run high octane unless you get stage 2. IF i am wrong, chew me out. later fellas

 

Thanks for clearing that up. I was wondering about this earlier today as I was pumping gas.

EDIT: Don't put anything but 93 in my SS/SC, BTW.

 

Check your owner's manual, i'm sure there is something in there about running at least 91 octane...........

 

http://www.edmunds.com/apps/vdpconta...3/pageNumber=5


Look under "Vehicle" heading at "Recommended Fuel".

I believe the manual says "Premium recommended, but not required", so: Are you positive that your PCM/ECM isn't just compensating and you actually could be running more efficiently if running 91 or higher?

 

My owner's manual says that premium is suggested but not required.

 

Read two posts up^^^^^^^^^^^^^^

 

You are wrong, but I won't chew you out. It's safe to run 87 octane in the SS/SC, but it'll kill a ton of power as the computer pulls a lot of timing to keep the fuel mixture from detonating. Fill up with 91 oct for the next couple of tanks and you won't want to go back.

 

You are correct, sir!

 

Consider this your chewing, a SS/SC can run on 87 but the car pulls back on the timing and it says right in the you will not have as much power. The manual reccommends 91 or high, what the car was designed for. Try running a few tanks of high test though your car and then see how strong it runs...

Remember if you have any questions RTFM

 

^^^^^Echo Echo

 

Yeah I switched to premium today. My new car feels kind of sluggish and my fuel economy is blowing ass, so I want to see if this corrects it

 

It will, but it'll take a full tank or more to notice the full gain. It takes a while for the computer to "relearn" and adjust to the new and better fuel type.


-Edit: Just realized you have the 2.4, so you might not notice a big difference out of 91+. I'd say 89 oct should be the ticket for that engine.

 

Oh yeah, I've learned enough over the years not to expect immediate changes from pretty much anything. Especially those meds they keep putting me on

 

Whatever model you have, RTFM, thats why it is there to answer these kinda of questions.

 

It is a shame that not very many people anymore actually adhere to the RTFM rule.

 

what was weird was that the 2.2L OHV in my 98 Cavalier would NOT run at all on 87 octane... any 87 octane. It would ping and just dog out. I started running premium and it perked right up, ran quiet and strong... never did figure all that out the 3 years I had the car.

Scott

 

Hey, 87 works fine for me and i save a buck or two.

 

Officially, GM recomends using premium fuel (Octane rating of 91 or higher) in both the 2.4L and 2.0L engines. It also states that a lower octane fuel (no lower than 87) can be used safely, but with a noticeable power loss.

A 2.2L would see no advantage running premium fuel.

 

Actually... octane is officially a performance rating of gasoline. It specifically tells you the tendency of the mixture to resist knocking or early ignition. It's basically a rating that tells how the mixture will perform compared to pure hydrocarbon octane (which would have an octane rating of 100... no premature ignition).

Correct.

I have actually never heard of this. I'm thinking it's not accurate. The only bad effects of using a high octane fuel in a non-performance engine (that is an engine with lower compression) that I've heard of is the fact that not all of the fuel burns sometimes. This can cause build up in the catalytic converter.

Incorrect. If you're speaking to the average driver, you should say, "Always run the recommended fuel unless you notice any engine knocking. Then step up your octane rating for a few tanks to see if it improves."

You can run the recommended fuel, but it might not give you the best performance. Regular fuel is recommended for the 2.4, but the 2.4 is a high compression engine (10.4:1 I believe). I can actually notice (without dynos or timing) that 91 or higher gives noticable performance gains.

It basically boils down to this... 87 will be just fine for 2.2 and 2.4L ecotecs. Using 89 won't hurt. Using premium will probably not provide any benefits to a 2.2L, but will give a little extra kick to the 2.4L. If you have a 2.0, you'll want to run premium. The fact is, if you want performance out of your vehicle, you should know the engine and mechanics of the engine well enough to know what will and will not benefit your vehicle. If you don't know that much about your vehicle, you probably shouldn't be worrying about how much power you can squeeze out of it.

 

When I was in school we did an isotipic lab on different octane fuels. We used something like 87, 91 and 93. In normal cars I usually get mid grade (~91) because the isotipic difference b/t 87 and 91 was very noticible. The difference b/t 91 and 93 was noticible however the margin was about 500% smaller than the difference b/t 87 and 91. Interesting stuff I think. I still use 93 in my SS though because its only about 5 cents difference where I live and she gets nothing but the best.

 

Im glad i dont have to put prem gas in my car. Prem cost over $3 a gal. But in the past ive tried the higher grades in other cars ive owned. No changes so if my 2.2 takes 87 so be it. All im waiting for is my k&n filter an i'll be happy

 

It doesn't make sense to me why you'd buy a F/I car and not use at least the premium fuel. What's next? 10W-30 Conventional oil? Yes you can run both of these in the LSJ (not that I would recommend using Conventional oil at all) but why risk running the car in any way other than what the manufacturer recommends?

This car is one of the hottest running cars I've owned (engine wise, I've had a 300+ HP 5.3 and 5.7). You have to consider that you are making more than 200HP out of a 4-cylinder engine. You can tell it runs hotter by touching the hood after a long distance run. You can almost fry an egg on the hood. You can save a little $$ by paying for 87 octane or conventional oil. If you do however, I would recommend putting that $$$ in the bank because you'll probably have some issues with the engine later on.

 

wait, Premium at every pump Ive filled up at is 91. How do you get 93?

also. 91 is 2.99 right now. damn it!

 

i have the 2.4 and i use nothing but Sunoco ultra 94 octane gas...i have actually noticed a power difference between lower octane fules and the 94 octane i use...of course i pay 1.20 cents per litre