I just purchased a 2006 cobalt ss non-supercharged. According to Haynes Repair Manual I have a "B" motor (2.4) and claims in the book that I need to use 91 Octane. Is this right? I was told that 89 Octane is OK. Which one should I use?

 

the 2.4 can take 87 octane, 90% sure. wait for one of the SS/NA guys to chime in though just to double verify

 

beats me never had an SS na 2.4 but ive always ran premium in both my balts

 

91 recommended but 87 is acceptable.

Basically, if you want full power you need 91 (premium), but if you're just putting around the city 87 is fine.

The computer has a map for both fuel grads as far as timing goes, so either is fine.

 

in my g5 gt with the 2.4 the book says you can run 87 but performance will be less and you may hear "spark knock" so 91+ is the way to go

Denlou beat me to it!

 

i basically have the same car as you i own a 2.4 sport cobalt and i was using 91 and my car didn't like it, my exhaust smelt like sulfur and i wasn't getting bad gas mileage, so i switched to 89 and my car runs smoother, i get 26 mpg city and their isn't a bad smell. and its a little cheaper

 

.... theres something wrong with ur car, theres no reason ur car would run worse on a high octane if its factory tuned to run it... Could be your mods you have, might need a proper tune

 

It will run on either but you might notice a slight drop in performance. I know if I run my car on 87 octane it runs like **** so I always use 91+ octane.

 

lol I'm too damn cheap to spend any more on gas than I have to.. i put regular 87 in and it runs just fine, I threw Premium 93Oct in once and didnt notice any difference in acceleration... a bit better mileage though

 

87 in the tank and mine knocks like crazy at low rpm's.
91 in the tank and I can mat it from idle, no knock.

GM may say it's ok but I would rather not take the chance of blowing a hole through a piston to save what, 2-3 bucks a tank?

 

Mine runs the best on 91... I have just a couple of mods, but I put 87 in it one time and noticed a loss in throttle response..

 

Ever since my first fill-up I've run 93. If you look in the owners manual, it says something like "premium fuel is reccomended". You CAN run lower, but I don't.. I figure that I'd rather pay the extra few dollars a fill-up and not have it run like ass.. I was even putting in 93 when it was over $5 a gallon, so man up.. lol Oh, and mine has 72k on it.. So it's had quite a few fill-up's..

You should always use AT LEAST 91 if you have high compression or boost.. We have higher compression..

 

I dont hear any strange sounds at 87oct..

 

Y'all need to refer to the owners manual.. lol

 

91+

I always ran it, but when I first got HPTuners like... back when I ordered it...I had my 2.4 and decided to log some 87 octane.

Cruising

WOT

Part throttle

Made me fill it right back up with 93

 

Exactly. It only costs like a dollar extra a fill-up for 93. Don't be a cheap ass.

 

Stay with whats recomended. It's what, a 10-20cents difference? It's not a big deal.

 

GM reccommends 91+ on the stock LE5 and LSJ motors. That being said, if you use under 91 premium, the knock sensor will notice and dial back the timing.

For those who have GM Stage 2/3 and I'd imagine any variation of the SS/TC, you'd have to run at least 91 at all times.

 

Exactly. High compression and/or boost requires premium. You don't want to buy 93? You should have bought a different car. I was putting 93 in it when 93 was over $5 a gallon. So don't be a cheap-ass.

 

Before I realized I was Stage 2 (I bought the car used with it, I thought that it was a stock pulley since the price was so low), I was running 91. After realizing it was Stage 2, I started putting 93 in it.

Anyways, I was driving a L61 G5 whenever gas was listed at RA.PE/g, so I could get away with 87.

For those who are supercharged and have an abundance of E85 stations, you can look into that option if you want to get the tune and upgraded injectors needed for it. I'd spring for E85 myself, but there are not a ton of E85 stations in Pittsburgh, let alone most of Western PA. The only stations carrying E85 I know of off the top of my head is Robinson Sheetz. E85 is cheaper than 87, but has an effective octane rating higher than that of 93.

 

This.

Switched between both when I had my 2.4 and all was ok. Honestly never noticed a power difference between the two.

 

what if my 2.4 has been using 87 since last summer, and i just decided to fill up with 91 or more? would i have to drain the gas already inside? or can it mix, untill 87 is run completely out?

 

No problem with mixing. Many gas stations mix 87 and 91 together to make 89 anyways.

 

i run 93 because shell only has 93 and i only run the best gas. i used bp and sunoco for a while 91, and when i switched to 93 i didn't notice any difference but i figured that cause it's not tuned for 93 only 91. but running 93 instead of 91 won't harm anything right? or am i better off running 91 cause the car is tuned for 91?

 

Your owners manual has this information in it.