xplane

Are our cars supposed to run better on 87 than 91 octane? cause i did a test on my car and have alternated from 87 to 91 for the last 8 tanks of fuel and i get better performance, the car idles smoother and starts a lot easier with 87. why is this? i mean with 91 in the tank the car will stutter and barely pullitself until it gets to about 120*F and then it runs fine but sill not silky smooth like it will with 87 also there is a noticeable power difference. not just oh i think its going faster i can race some of my friends and loose with 91 but will kick their A$$es with 87 weird. i dont understand it but mabe im just a moron. i was for shure it would be the otherway around.

Naft

the number represents the fuel's resistence to combustion. higher octane fuel allows higher compression and more ignition advance, but doesnt actually make more power directly. if your ignition is weak or on its way out, its possible your car could have trouble igniting the higher octane fuel with the same compression ratio(and intake air temperature), causing occasional misses that will rob you of power. it is advisable (and economical) to operate your car at the lowest octane level that provides a safe margin from predetonation.

urbanhunter44

iTrader: (3)

What he said.

Another good rule of thumb is that anything over 10:1 CR, you'll probably want to run 91/93 in. My car makes 10.5:1 CR (stock cr I might add) and it even says in the owners manual and on the gas tank door to run at least 91 in it. Boy does it ping bad on 87!

Gumby

I got much better mileage when I would run ultra 94.
But stopped when it got to be $1.65+

rx7speed

the mileage stopped or putting that type of gas in there stopped?


just to let you know the higher the price the gas is the more worth while it is to run premium. at least if you are taking advantage of it by upping timing or whatever else you are doing to need the extra octane.

my honda regular gets 32mpg on premium so far I have seen around 38mpg
it's worth it at current gas prices to run premium but then again I have to up the timing to take advantage of it by quite a bit

Gumby

Both, I use to get my best mileage on ultra 94, then stopped buying it. Still get decent mileage.

2_point8_boy

WHHHAAA!!!! It's $2.65 for 87 here! :-P

rx7speed

muahahahaha
gas just dropped to 2.11 here in boise for 87


now for my mazda if I could only find more places selling 86 octane or even more preferable 85

Dale

iTrader: (12)

I noticed me 3.4 (9.5cr)ran a hair better on 93oct. It would ping less, which would let it advance timing to create the better power.

If I am careful how I drive, I can get 93oct, for the price of 87

Gumby

I hear that but its that initial fill up thats scary. Higher grade gas isn't suppose to do anything for our cars but some how the car ends up using less gas. If I was rapper rich id run ultra 94 all the time.

My Mom found gas for $1.84, I got some for $1.93 yesterday.

Dale

iTrader: (12)

gumby, I didnt notice any mpg difference that I couldnt contribute to driving a little nicer.

I have to make a tank of gas last monday to monday, or tues to tues as I fill one car up on one day, and other the other day.

If I fill up any other days for either car, I have to pay full price of 93oct at 2.20'ish a gal. 87oct is floating right at 2.00 right now.

rx7speed

whats the difference in gas mileage you are getting between 94 and 87? whats the price difference?