link146

Just curious...anyone ever run simply regular 89 oct fuel in their C32?

The reason I ask is because I know that all modern cars are equipped with anti-knock sensors which will adjust for which ever fuel you are running. I used to run regular in my 02 325xi (which recommends that premium be run in the owner's manual) and noticed little-to-no difference in performance. The Bimmer did, however, get slightly less mpg on regular than premium (it was such a small difference that there was no question that the lower price of regular was a better deal).

Anyway, I know that the C32 is a much different beast than my old 3-series; re: timing, compression, hp, etc. However, like all other modern cars, I assume that the C32 is equipped with an anti-knock sensor. Thus, my hypothesis is that regular can be ran in a C32 without destroying the car. Whether the gas mileage or the performance turns to **** when run on regular, I don't know, I have never tried it.

Anyway, I just wanted to put the thought out there for ideas and comments. If you have an educated opinion please chime in, but if your answer is something to the tune of "just do it because the owner's manual says so" or "premium fuel is better" don't bother responding. I simply want a good reason, supported by factual/scientific logic, data and reasoning why I should not run regular fuel like I have done so many times in the past. Just for one more example, I rode and owned several sportbikes in my day and I recognize that their engines were virtually tuned for the track and I have even done after market tuning (intake, exhaust) and fuel mapping. I ran both premium, regular and race fuel in them. The difference between premium and regular is negligible at best. The difference between street fuel and racing fuel is noticiable, however, I don't know whether it improved my times or performance or whether I just enjoyed the intoxicating smell of it.

Thank you for your input on the topic.

hooleyboy

You are 100% right about the knock sensors detecting knock for fuel types. So yes just like 100oct will advance timing and add power. 87 or 89 will pull timing.

Not to go to far OT: the knock sensor is the reason running race fuel adds HP in our cars. It is a myth to think otherwise.

Now running a low grade fuel in a FI car could be asking for trouble. Even having time pulled out by the ECU might not be enough to stop detonation. I've never done it, so you better hope the knock sensor is working. I'd chalk this one up as risky.

ScottW911

Why would you purchase a fine automobile like the C32 and cheap out on a few pennies with non-recommended (and potentially damaging) fuel.

Sell the MB. Get a Civic.

TemjinX2

lol...just ask c32used what 87 does to a c32.

jturkel

+1

i dont know why you (the OP) would want to put regular gas in it....seriously. why?

ML500K

what about changing the fuel settings with the star diagnostics from 91 to 93? anyone try that? Is it worth doing?

link146

I appreciate all of your opinions, however, no one answered the question. Whether I am cheap or not has nothing to do with it...I simply asked a question seeking an educated opinion in either end of the spectrum.

Hooleyboy: I understand your point, but like I state above, I have run reg fuel in cars/bikes that call for prem and have noticed little-to-no-difference.

Basically, my question can be boiled down to this: Will running lower octane fuel in my C32 hurt anything other than performance? If yes, why?

If you can supply a well reasoned answer to that question, please do. If you want to ask me why I bought a C32 and tell me to buy a Honda Civic don't waste your time and go read a MB owner's manual. If we did everything a MB owner's manual instructed...no one would ever touch their car and drive straight to the dealership for every problem, however de minimus it may be.

link146

C32used: what does 87 oct do to a C32?

jturkel

GO BUY A HONDA CIVIC

MRAMG1

Okay where to start

1. Blown head gaskets due to pre ignition/spark rattle which GREATLY increase combustion pressure
2. Burnt exhaust valves due to over heating from pre ignition
3. Cracked rings
4. You have to be kidding and why didn't you go buy a GEO

I quit

c32AMG-DTM

Okay... lot of aggression on MBW these days for whatever reason. IMHO, you guys are being too tough on this one - it is an interesting question.

CA and AZ folks run regularly on 91 - some have speculated that they can get "crappy" 91 that's more like 89. If cars with intake, 185mm CP, tune, etc. can run "crap 91" without grenading the engine - I think it's likely that someone could run 89 (mid-grade) in a stock pullied and stock tuned C32 without adverse effects. The OP didn't ask about running 87 (regular) - but my curiosity has been piqued - what happened to c32used's car by running 87?

TemjinX2

it was a subtle joke. Basically last yr c32used posted a thread about how he was having problems with his engine.

We all thought there was something seriously wrong with his car. Until later in the thread he posted he put 87 gas into the car. Never i found it it was 89 gas, not 87.

Basically after he put premium back into the car, the car ran perfect again. He basically got flamed for a month about it...it was all in good fun. But you can probably find his thread about it.

TemjinX2

To the op...you can try it out and let us know. Its 91 in ca because there emission additives that changes the octane rating to 91 from 93. California 91 is still higher then other states 89. There rating is still the same across all 50 states.

Its about a 10cent difference between 89 and 91. 14 gallons x .10 = $1.40?

you want to run your car below factory spec to save $1.40?

Phil C55

There are a bunch of guys on the Ducati forum that swear by lower grade fuels in even bikes like a 1098. I only used premium 92-93 octane in mine because that's what Ducati called for, same thing for the C55, it only gets premium. Some of them even claimed increase in performance.

TemjinX2

you lose mpg and performance when you run lower grade fuel then the manfacturer recommends because the gas is igniting before its suppose to so the car retards the timing to compensate.

So any money you save on the lower grade gas becomes a wash since your losing mpg.

There's a huge thread on it on the w203 forum. You can check there...most of the common questions of premium vs regular has been answered.

generally speaking

low compression gas + high compression engine = BOOM!

gt4awd

There's a big difference from running lower grade fuel in say my 2004 350z that says it requires premium. I'm sure it would be fine... However, the C32 is supercharged, and requires higher octane to achieve correct air fuel ratio. The manual states to stay off the throttle if you run lower octane, and to only do so if there is no option for higher octane fuel.

MRAMG1

Octane buy itself has nothing to do with A/F ration, what it does affect is the spark advance and detonation properties. The latter you do not want under ANY circumstance for my above reasons. I popped a head gasket on my supercharged stang do to some **** poor gas a few years back. My A/F guage showed nothing wrong, but the motor spark rattle hard, only once, and I was left with a milk shake in my oil

As far as performance increase or MPG, your car will ALWAYS get the BEST performance/mileage with the optimum octane for it. No more, no less is required. Run too much, and you will LOOSE both. Its simple physics guys. Believe it or not. The best octane you can run is the one that allows full timing without pre detonation and this will ALWAYS make the most power and give you the best mileage.

Translation, if your car has NO detonation on 91, using 93 or higher will only hurt both. Noiw tune it with more advance, and you WILL need more octane to suppress detonation

MBH motorsports

To the ducati guys feel this is because the bike revs so high? Do they think with the high RPMs they simply can not burn all of the slower burning fuel at such high RPM's? So they use a lower grade fuel that burns crazy fast. This is very interesting to say the least. If I didnt fear detonation, this would mostlikey make sense to me.

I think diesal fuel burns real slow, Thats why (guessing) some diesal trucks redline at 4k because they cant burn all the fuel at any higher RPMs.

Phil C55

Not sure what they are thinking, some just say the bike runs better. A 1098 is twin that has nearly 4" pistons, so you don't rev one past 10k rpm, but it is a high compression motor. 150 hp out of 1.1 liter is pretty healthy and so I would think it needs at least premium pump gas.

E55AMGFan

Any performance car especially boosted needs the highest grade available. 93+ and in Cali, the 91 water down stuff cuts it.