Will it run on regular gasoline? - United Bimmer Community

**dixonjab** · 10-15-2007, 08:56 AM

I am considering the purchase of a 2002 BMW 330 convertible. The specs state that it requires premium fuel. I read in an article recently that some vehicles can sense the use of regular(87 octane) and adjust the engine to satisfactorily run on regular, although with some loss in performance.

Questions:
1/. When the specs indicate "premium", is it calling for 89 octane, or something higher?

2/. Will the 2002 BMW 330 operate satisfactorily on 87 octane? Performance is not an issue with me.

**celsdogg** · 10-15-2007, 10:23 AM

in essence, most modern cars have knock sensors that retard timing in the event of the predetonation, which is the number one reason to use high octane fuel. the higher the octane, the more the fuel/air mixture can be compressed. generally, higher octane fuels should be used in engines with higher compression ratios. other than additives, there is no reason to use high octane fuels in lower compression engines like my 8.8:1 E30, which sees no difference between regular and premium fuel. however, if may become necessary in lower compression engines like the M20 in my E30 due to carbon build up and other gunk in there. this is because the gunk changes the compression ratio to be higher than standard, causing predetonation. it can be remedied by the use of higher octane fuel or a head job. (dont take that outta context).

this being said, i do not know the compression ratio of the M54B30 that is in the 330Ci. You will have to figure that out, but no, damage would not be had in the short term because the computer will retard the timing which equals lower performance, which you dont care about. HOWEVER, i would not recommend the use of lower octane fuels for long periods of time in an engine with a higher compression ratio.

all these facts ignore the different additive packages that gas vendors put in their gasses. Some argue that the additives placed in the higher octane fuels can help prevent the buildup of carbon and other crap in your combustion chamber, thus giving you the best fuel economy and performance, which i am sure is true to an extent.

that brings up the other point of fuel economy. if the computer retards the timing, then your engine will not be running at best efficiency, thus probably wasting gas and perhaps polluting (if you care about that, im like whatever to a certain extent). so it seems to create a fine line between not being efficient with the lower octane fuel, and being more efficient with higher octane fuel, which again depends on the compression ratio. so thats worth finding out. it should be listed in the owner's manual that comes with the car.

**Dudesky** · 10-15-2007, 01:50 PM

89 octane is the minimum for the M54B30. That is the lower portion of the adjustment range that the engine can accomodate. 89 is bad, but 87 would just be even worse. As 'dogg said, you don't stand to gain anything from using lower grade fuels. In fact, your gas mileage will suffer as a result.

Rooz · 10-15-2007, 02:09 PM

Premium = 91 octane or higher = Supreme

nick_318is · 10-15-2007, 06:23 PM

I would run premium.

**Numark318i** · 10-15-2007, 06:36 PM

premium.

also use top tier gas, for example chevron. I have heard from numerous dealerships that most US gas have additivies that are actually bad fo the engine. for example arco.

Try and only use chevron or shell or other brand name gas.

i notice my car idles 200 rpm lower on higher octane.

**DonB** · 10-15-2007, 07:10 PM

I know here, most people will use regular, but regular is 95 octane here..and they use Super 99 octane if they're doing a track day...I've used both and haven't seen any difference.

**MTurboPower3** · 10-15-2007, 08:19 PM

You can run regular if you want to be cheap about it, but it won't have the same pop as it does on premium. But its up to you what you want to do.