JZMD1

MB 208,
The "powers that be" have limited the maximum octane fuel available here in Las Vegas to 91. Will the performance of my C-32 be enhanced by increasing the octane number?
Do you suggest the use of either octane boost or the addition of several gallons/tank of VP Fuels High Performance (99 octane) Unleaded to accomplish this?

JamE55

God question? So will getting a higher octane rating increase performance?

awiner

Last month in Car & Driver they did a few tests to determine what thye very subject asks. The resluts were: If you use 91/92 octane in your vehicle that needs premium fuel, you are fine. Anything more is a waste of money for what you would get out of it. As far as vehicles that can run on "Standard 87" octane, C&D found that putting 91/92 octane in these vehicles did barely nothing for performance/driveability.

Moral of the story is to use the RECOMMENDED grade/octane of fuel that your vehcile model suggests.

Your mileage may vary......

Mach430

True, but that is partly due to the ECU's fuel/air ratio. I think that an ECU tuned for 92 would outperform an ECU tuned for 91, hence the 105 octane.

JamE55

So i guess the answer is

young

i don't think it makes a difference. i think the engines are designed to have a certain minimum (otherwise, you get knocking/pinging). in the philly area, all the supers are 93 but i think this is so that they can charge more.

for those that are in CA and don't know about NJ, gas is always cheaper there by like 10¢ and its only full service! first time i went to a gas station in NJ, they yelled at me b/c i started pumping my own gas. who knew that they had a law like that?

JamE55

hey young!

you're kidding right?? they yelled at you because you tried pumping your own gas?? WTF??

Robert ...RAB

Actually, it makes a lot of difference between using premium vs. regular unleaded. Dyno tests have shown a significant loss of power in a new M-B using regular unleased. The ECU will retard the timing in order to conpensate for the lower octane and that equals less efficiency. The money saved in lower cost fuel is lost due to a reduction in throttle response, HP, and ultimately fuel economy. The last test I read showed a negative 19 HP and a negative 22 lbs/ft of torque when using 89 octane vs. 91 octane.

When I got my new C280W last year, I tested several different brands and octane ratings and was quite surprised how much better fuel economy I get with 91. Even a significant difference between Chevron and Mobil was noted. Yes, I know, it's all supposed to come out of the same tank but Chevron gets me an extra 25 miles per tank everytime.

Fully service only? In Newport Beach, CA you would have to take out a second mortgage with a co-signer to pay the price of full service. It's a LOT more than self-serve. ...RAB

Mach430

It's illegal in Oregon to pump your own gas.

kingman18

.

Renok7

What if you are a NFL player with a Phd in Gas Pumping?

JamE55

Phd in gas pumping?? lol!!

BrabusCClass

I know for a fact that lower octane gas makes you lose horsepower. Its is very evident in Turbo cars because you literally cannot boost. We better the octane rating the higher you can boost. In my C36 I really felt a difference when I pumped 100 octane racing gas. I was curious and they say you are suppose to mix it but I really didnt. Anyways, I I filled half a tank up and felt the power immeadiatly. All I can say is WOW. If it wasnt for the expensive gas price for 100 octane I would always have put it in. Its around $5 a gallon ($4.98) lol. I did it once in a while so it can really clean my injectors (thats a excuse I did it cuz it was fun when I hammered the throttle).

darkLCD

Brabus, did you fill up at a Unocal76 for the 100 octane gas?

s810

We have plenty of sick ******** here in California but we can pump our own gas. I'm not sure how limiting access to gas pumps to only a professional service station attendant reduces the incidents of arson. I'd bet it has more to do with somebody with political clout having a vested interest in limiting gasoline distribution giving lots of money to the politicians who are willing to maintain the status quo while the vast majority of Jersey drivers don't care one way or the other. And are motorcycle riders generally considered more stable than automobile drivers?

It's good to know that these laws exist out there, just in case I'm in New Jersey or Oregon and try to fill my tank. I don't want to repeat a faux pas like the one I committed the first time I tried to buy beer in a grocery store in Pennsylvania or stood there waiting for the cashier to tell me the grand total for the T-shirts I was buying because I didn't know there wasn't any sales tax on clothing.

Lightman

Thats funny, the same thing happened to me in NJ. I tried to pump gas and they were yelling. I thought they were messing with me on the law about full serve!

As far as the octane goes, you will acheive the best performance using the recommended octane. If your car specifies 87 (like my tahoe) it will actually have the best performance on 87. Generally the higher the octane, the slower the fuel burns and at a lower temp. This is to accomodate the higher compression ratios of high performance engines, to prevent detonation. Using a higher octane than your car is rated for is not detrimental - in fact a lot of gas companies claim their high test has extra additives/detergents, as well as fewer impurities that may clog fuel systems/injectors. Higher octane will definitely not improve your performance though, if that was the original question. If you were to say put 110 octane unleaded race fuel in your car, most likely it would run worse than on 91, as you might develop a rich running condition for a while until the computer adjusts(if it will even adjust that far). Hope this helps,
Dave

Spyke

It is untrue that higher octane gas burns slower to control detonation. If it burned slower, detonation would actually get WORSE. A mixture doesn't detonate because the flame front gets moving too fast. It detonates because the unburned mixture eventually auto-ignites, all at once. No flame front at all, just a big bang. This creates a shock wave in the cylinder which rattles the heck out of everything and bounces off the cylinder walls and makes a neat knocking noise... Higher octane gas can resist auto-igniting under a high temp/high pressure condition longer than low octane gas. Actually the trick is to burn the mixture faster so it's all gone before it auto-ignites... hence dual plugs in large bore cylinders, or swirl in the intake charge, etc...

Comparing 110 octane race fuel to pump gas is an apples to oranges comparison. There are more differences in these fuels than simply the octane number... compare 89 to 93, sure, but when you get over 100 you're looking at different chemical bases...

Lightman

Well ok mr engineer, thanks for the technical lesson, I guess I was misinformed about octane. My whole point however, was that the person should use their recommended octane and that the car would run best on gasoline of that rating....which I'd say is still sound advice.

young

oh, sure. i agree w/ that.

i meant between 91 vs 93. i know that my car's ecu is set for 91 but all the local gas stations are 93 octane. i'm going to get it reset for 93.

as for 87 vs 91, definitely use the recommended octane. i had a nissan that used 87 and using 91 was worse for the car.