The manual says: The Lancer 08's 4B11 engine is designed to take an unleaded fuel with 87 octane rating as minimum. I dunno if I'm right because I'm using a 91 octane rating of Exxon Mobil fuel.

Any thoughts about this octane issue of Lancer 08? and What y'all using then?

Tnx.

Your compression ratio isn't high enough to necessitate that high of octane.

The price difference between 87 and 91 is only 10 cents, actually.

Also, why does the manual says "minimum of 87"? so literally, the engine can take a higher rate octane like 91 because it didn't say any limit after all.

It is my 2nd fulltank of 91 octane now, maybe i'll switch down to 87 if anyone here will say that 91 is bad for the engine.

I just took a three and a half hour drive down to Sierra Vista from Phoenix. On the way down I had Chevron Plus and I averaged about 66mph and 30mpg. On the way back I had a full tank of Chevron Premium and averaged 68mph with 32mpg. You have to weigh the cost of 10 cents per gallon versus an extra 2mpg. Thats about an extra 30 miles for $1.50. You probably don't make more power but I thnk premium burns a little cleaner. I'm probably going to go with the middle grade of Chevron.

Simply put, your just wasting money.
Just like Unibanger said your not tuned to meet that high of octane. Will your car run, yes. Will it hurt it, no not really. The only thing that is happening is your car thinks it's regular gas so the readings may be a little off (you running rich) but not by much... and mistu is known for running rich (as far a lancers go, idk about 2008s) stock. Its really not much of a big deal in a short run. The gas is cleaner but your car doesn't know the difference between the two unless you tune it for it...
here,s more stuff on OCTANE<--clicky

The car doesn't know the difference? What exactly do you think all of the sensors and emissions systems are for? Why are there multiple fuel tables and ignition tables for various conditions? It's because we (and I say we because I help develop the vehicles you drive) specifically test drivetrains with different fuels from different companies of different grades. Thats exactly why the owner's manual says a "minimum of 87 octane", because 87 is ok but 91 is better. The truth is that we tell people to use 87 because your annual fuel cost will be less and we will sell a few more units because people view the vehicle as more fuel efficient. Would you rather see a sticker that says premium is required and you get 34 MPG or a sticker that says 87 Octane Minimum with 30 MPG. It's a trick question because we don't show you the first option.

Alright then, at least I'm on the right track from the start, so I'll stick to 91 Octane onwards. A $3 a month difference (for a twice a month refill) is not bad at all especially if my engine runs happily. :)

And Kbanks, is it normal that during a break-in period, the MPG usually starts low? In my case on my 2nd refill, I just got 15 mpg average on city driving here in nYc. Hope It can improve for at least nearer to the advertised Lancer 08 mpg, which is 22.

use ONLY 87 octane. the car does NOT benefit from higher octane, and in fact can suffer cold drivability issues from it.
You may also loose a small percentage of milage.

DO NOT waste money on 91 octane. You gain NOTHING. absolutly NOTHING. The engine is NOT tuned to need it.

Minimum, meaning the car is sold world-wide and other countries actually have 85, 83 octane...

91 octane is dangerous for an 87 octane, it will decrease the life of your seals and other vital parts. it burns better but creates a bigger "bang" when it ignites, thus creating more stress on an engine not designed for it.

It doesn't create a bigger bang. Octane is "like" a rating of it's resistance to burning. This probably isn't a good example but if you put a puddle of 87 octane fuel next to a puddle of 91 octane fuel on the ground the 87 would evaporate first. Combustability or "explosivness" if that's what you want to call it is actually controlled by the engine when it decides how much fuel to add to the ammount of air entering the cylinders. That's why theres air fuel ratio. If the "explosions" are too powerful, damaging, or hot (ie. running lean) the ECU will tell the injectors to stay open longer, to decrease temperature and richen up the mixture. With the MIVEC engine it will retard the timing and adjust the camshafts if necessary. I don't know how else to explain this. Premium is better that's one reason why it cost more. And to give you nay-sayers some credibility, yes too much octane is harmful to your engine, assuming you're trying to use nav-gas or c-16 or straight rubbing alcohol to pass emissions or something.

actually, none of thats true.
the only real issue with using higher octane is that you piss away money. HOWEVER, on a car not designed for it you can suffer cold start hesitation, a slight loss of milage, and an actual (however minute) loss of power.
higher octane is more resistant to ignition, and burns slower. Those are great when the car has high compression and is tuned for it, but they are not great on a car with lower compression thats not tuned for it.
use 87 octane in your lancer.

:thumbsup: i stand corrected!

its not as though it even burns slower its just that its less likely to detonate due to temp and pressure with out the spark to fire thats why you run higher octane in high compression and turbo/super charged application to prevent knock/predetonation due to the higher cylinder temp and pressure and anything higher than called for or needed to prevent it is pissing your money away

I run 87 I drive 600 miles a week 90% highway and I average about 36 mpg in my 5 speed oz so I don't think the mileage with 87 is all that bad

ok wow i get like 17 to 18 mpg on my lancer in the city. i have a cat problem right now that im getting fixed but is my mpg normal? i dont really like it seeing as to how im filling up at least one or two times a week and running on regular.

once you get your cat replaced you should see your mileage shoot up a bad cat will kill your mileage

a failed cat will not affect milage at all.

evedentaly you have never seen or had a cloged cat it will kill a car and choke it down to nothing

if you have to much back pressue in your exhaust it will cause issues

so my milage will go up or not? :huh:

when you currently give the car alot of gas dose it seem to bog down if the answer is yes to this then your cat is getting or is partialy pluged and with my experiece yes it will go up but by how much your going to have to wait and see