So I read a thread here the other day about putting high test (91 octane) in 2.4s instead of the cheap stuff and somebody complained that the salesmen told him that it didn't make a difference and there was a big debate, well I was in the same boat, salesman told me - quote "the SC model needs high test but you'd just be wasting your money to put it in the 2.4L model" so after reading that thread I said f*ck it I'll try it, only a couple bucks more for a tank whatever, well the first tank the engine seemed to be acting a little strange, so I thought it's probably just adjusting whatever. so today after work I refilled with high test again and I drove to visit my gf at uni and holy ****! it was like a new car!! it sounded better and felt better, and i got alot better gas mileage!! normally when i get here from a full tank I have between 1/2 and 5/8s of a tank left (when the weathers good maybe just over 5/8s) tonight I got here and had just barely over 3/4s. I WILL NEVER PUT THAT CHEAP **** IN MY CAR AGAIN!!! high test only from now on, just wanted to tell anyone with a 2.4 that's not using high test, START!!!! it will not cost you more in the long run and you'll be doing your car a favor at the same time!!

 

yea never put that ****. 90+ always goes on my cobalt, nothing 87 or 89 or w/e dumbshit they have.

 

the 2.4 also has VVT, you should be using atleast 91, it even says so in your manual

 

you believed a salesman ?

 

2.4 should absolutely be using premium.

that salesmen should be neutered.

 

mmm heres my take on it...

with a lower grade octane, you cause knock (gas not detonating) in higher rpms, ive noticed this when taking my car to high rpms that i can feel it act "sluggish" and watch the rpm meter stop for a brief milesecond...

i use 87 in winter because well i am not pushing my car to its limits and its cheaper..in summer i use nothing but premium 91 octane...

it is safe to run these cars (2.4) off of 87 octane aslong as you are not redlining it...thats my take it on, i could be wrong could be right

 

LMAO SALESMAN STORY!!!!

So when i had my srt4, i came to the dealer to check a srt8 chrager... so the dude comes to me and is like i noticed ur car is making hissing and pshh sounds whenever you shift, i think u may have blown ur motor, sounds like a piston compression problem....im like ouch, do i still have warrenty, he's like open your hood, so im about to laugh and say cool, and he's like your not on the manufactured stock turbo, im like yea i am it just shiny* well i was big turboedd duhh* so he then calls his friends over, check out the problem, and they all agree it would cost me $$$$$$ to fix my motor, i said some other time and i drove off spooling the turbo and noticing them all looking at me. w00t.!!!

 

bahahaha i almost fell out of my chair! that made my night!

 

Man, switch it high test all year, it's winter here too right now, I'm in NB, it's only a couple bucks more and you'll make it back in mileage

I'll admit it, I'm guilty of believing what a salesman told me... it's my first car I'm still learning... go easy on me, at least I'm trying! and I'm willing to sacrifice my pride to make sure nobody else is doing this

 

meh ive ran it all winter now, ill prob switch back sometime soon, see the thing is..shell doesnt pump the gas for you..and its cold as **** outside..and i dont like co-op premium..lol

 

2 misconceptions i see in this thread so far


1. premium doesnt give you any better mileage
2. knock isnt fuel not detonating, its fuel igniting before (pre-ignition) or after (detonation) the spark

 

crap i thought the 2.4 ran on 87..

 

thats what i ment thanks

 

im guessing you didnt do a whole lot of research before you went and bought your car ?

 

who?

 

the OP.

 

i asked a few people who have 2.4s wut they used and they said 87 was doing ok for them..

 

most people dont have a clue what the octane ratings mean, or are for anyway.


the great majority of the population think premium is an optional choice, that burns cleaner and gives you a little better fuel mileage.


All of which are incorrect.

the 2.4 engine is tuned for premium. if you dont use it, you are getting knock.

 

indeed, does it not just ignite better..creating less knock?

btw if you reply to this, congrats on 10,000 post

 

man I have never gotten to my gf's place at uni on a 1/4 tank before, I've driven here many times and on different trips i was going anywheres from 90km/h to 180km/h, during hot sunny weather, in the middle of the night with the moon shining, in rain and during snow storms, I've done it all, but never on a 1/4 tank...

 

wind perhaps?

 

nope not wind, maybe tune ^^, i dunno, I just know I'll never go back, and like I said earlier, I'm willing to sacrifice my pride to tell others...

 

trust me. its not giving you better fuel mileage.

all higher octane fuel does. is have a higher ignition point.
pre-ignition/detonation usually occur due to excess heat and pressure,
therefore with a higher ignition point, higher octane fuel will put up with higher temps, without igniting and causing knock

its as simple as that.
no magic car cleaning abilities, no super fuel mileage qualities.....its just harder to burn.

 

if the car is tuned for higher octane and i was putting in lower octane, then is it at all possible that I'm just getting the mileage I'm suppose to be getting? and before I was getting worse than average? because I was getting some pretty shitty gas mileage a lot of the time... I'm not claiming to have amazing economy compared to everyone else or anything, I'm just saying my car sounds/feels better and I've never gotten from point A to point B with this much gas still showing on my gas gauge (hell maybe the gauge is broken I don't know) all I know is I'm not making this up

 

nope...you would have been getting less HP tho, because the ECU would have been trying to compensate by pulling timing, effectively lowering the combustion chamber temperatures, but the same air/fuel ratio would be used, resulting in the same amount of fuel used as premium.