92 Octane Vs. 89 Octane...big difference?

linod

Does anyone know what the big difference is
between 89 and 92 octaine...I just purchased a new
bmw 328ci and all over the owners manual it says to
use only premium gas, is there a big difference in
quality?

btroy

The difference is not so much in quality, but in the gas's chemical property that determines it's flash point, or resistance to premature ignition under compression in your car's cylinders. If your manual says to use 92 it's because your beemer has a relatively high compression ratio, probably over 10:1. Using a lower octane will cause premature ignition problems which can result in pinging or knocking, which is bad for the engine over the long-run. Your car's computer can compensate for that problem to a certain extent by altering the timing, but this will have a negative effect on performance. So, since you sprung for a high-performance car to begin with, you probably don't want to compromise it's performance in the interest of saving a few cents per gallon of gas. If so, you might as well trade it in on a Camry, which burns 87 octane gas and gets better mileage to boot.

By the way, there are a lot of other people around who's cars require 87, but they are burning higher octane gas thinking it will improve their performance. Most of them are wasting their money. If your car requires 87 and you are not having pinging or knocking problems, there is no benefit to burning 89 or 92 octane gas.

Also, at higher elevations you may notice that the gas pumps are labelled with lower octane numbers. That's ok, because with the thinner air at those elevations, lower octane numbers work well.

linod

thanks for you're time and info, i'm convinced, the only type of gas my bmw is ever gonna see is at least 92...thanks!

tonewheel

It's strictly a compression issue. My I30 calls for premium unleaded. My Reatta calls for 87, but it knocks so I use mid-grade 89...problem solved. My wifes Taurus calls for 87, and it runs fine. So many people use premium for "performance" or "power", or use a tankful to clean the engine from time to time. All grades of major gasolines contain detergent, so using an occasional tank of premium to clean the fuel system is a waste of $$. The only rule I stick to is purchasing gas from a major brand.

shcst12

Hi, can any1 help me this one, my manual recommand me to use regular fuel. Does that mean I should use 87, and higher octane (89 and 91)would be useless?? Pls give me some comment, thanks

shcst12

Does any1 feel the MPG is different when use different octane level?

erinsquared

If the car is designed to run on premium (92 + octane), you may see a loss of MPG and performance when running lower octane as the computer compensates by retarding the ignition (see post #1 in this topic). If the owner's manual specifies using regular (87 octane), the only benefit of premium is that sometimes there are higher concentrations of fuel system "cleaning agents". This varies depending on who makes the fuel. I run a full tank of Chevron premium every couple of tanks of gas to get a higher concentration of their Techron fuel system cleaner. This assists in keeping the fuel system clean.

I

kinley

Are you saying Chevron Supreme contains more Techroline and or Techron than their Regular or Mid Range gasoline? I consistently use Regular Chevron & have had wonderful results with it.

michie1

of sound is this knocking?

Sorry for asking . I'm new to cars.

bnormann

it is more high pitched than a "knock" IMHO. I think the term "pinging" better describes it. It may not have quite the ringing sound that you might associate with the term "ping", it is sort of a muffled ping, I guess.

Bruce

blacktooth

I ran across this topic and could'nt help but add my two cents. I looked into the octane issue several years ago when I got a jet ski and was making some engine modifications. I found out that 93 higher octane burns cooler and has less energy per gallon than 87 thus provides lower mileage. (Interestingly enough my ski runs smoother on sunoco 85 octane my 99 4x4 blazer runs just fine on 85 too).

Today's cars have knock senors that adjust the lean/rich to the type of gas your running. No need to waste money if your engine does not knock.

I did find that I got better mileage from Shell gas than others. A gasoline buyer friend of mine confirmed this. Shell just has more energy (BTU) per gallon than other gasolines. They refine their own gas while other buy it from the same terminal and add their own additive to make it "special". But at the root it's all the same stuff.

tpmiller1

The info on Shell is interesting. Aren't there other "name" brands that do their own refining, exxon?

tomsr

Numerous cars these days call for 92 but seem to run fine on 87.Aside from less mpg what is the
difference,is there going to be engine damage such
as deposits build up that cause noticeable pinging
after miles pile up.I also have heard that you should run a can of injector cleaner through once a month.Is chevron with techron a cleaner,Would I have the same effect by using chevron once a month?

bnormann

Check the "Engine Additives" Topic in this conference, it's #7.


Your host, Bruce

locke2c

re#8, 9

knocking and pinging are both used to describe detonation, where the fuel mixture is too lean or the ignition timing to advanced. it results in very high cylinder pressures because it's an explosion, whereas normal combustion is burning.

it often sounds like firecrackers. you should then be getting off the gas in a hurry, knock sensor or no.

the other common problem is pre-ignition, also known as dieseling. in a gasoline engine, it should cease to fire after the ignition is cut.

it sounds like a diesel.

-Colin

PS, regarding fuel... start with the mfg recommendations and experiment if you're curious or experience sluggish performance or bad gas mileage. (both of which can happen from too low or too high octane.) You will need at least 2-3 tankfuls of the "new" octane before your ECU figures it out, one tankful probably will not be enough.

carsancol

For the last six years I've been driving an '89 Plym Acclaim (from 53K to 153K) and I always used Amoco Ultimate. At times I would try to go cheap and put regular in or a different brand and it always seemed to lead to problems such as knocking or some other quirky behavior so then my wife who knows little about cars but has a good (female?) grasp on reality would say "I told you so"...so I would go back to Ultimate, pay extra, wonder why and drive ping-free and knock-free until my next bout with frugal gas. Now let me make some calculations 100K miles at say 22mpg means about 4600 gallons of gas. Say premium is 20 cents more than regular so thats $920 over six years or about $150/yr.
Was it a waste of money? From what I'm reading at this website, it sounds like it was and maybe my experiences using lower octane were only coincidental and definitely not scientific. Wish I knew the answer...
I just bought a '99 Camry LE 4cyl so I'm looking in the Owner's Manual and it states for my type engine (5S-FE):
OCTANE RATING: Select Octane Rating 87 (Research Octane Number 91) or higher.
(It goes on to say that the 6cyl (1MZ-FE) engine runs on 87 but that for improved vehicle performance 91 or higher is recommended.)
Don't know yet, since I'm still running on the dealer's tank of gas but I'll probably opt for
mid-range octane like 89, till I do further research and possibly, but no guarantee here, my wife notwithstanding.