Nice car! Question about fuel.

In top gear magazine a couple of years ago now, when Optimax came out they took 2 M3's and Honda s2000's and they ran one of each on Optimax for 10k.  They then dismantled the engines and looked and the build up of deposits.

The Optimax offered no extra performance but the engine had practically no build up in either engine, and they noted that some of it's additives are designed to help with preserving the performance and cleaning of things like lambda sensors.  This is all from memory at the moment but I will try and dig the article out.

sleeper wrote: knock-knock! getting the timing bang on with higher octane fuel will give a better pull though eh.

I suspect not. All the sensor does is detect engine knock. the ECU then retards the ignition until the no knock is detected. However if your car is mapped to run on 95 octane fuel and you put 98 octane in I doubt it is it going to advance the ignition. Why would it, the only sensor it uses is the knock sensor and by putting higher octane in you won't have any adverse effects.

However if you car is mapped for 97/98 and you put 95 in it will retard the ignition to prevent knock. This doesn't work with some engines though since a lot of high compression engines or high boost turbo motors can't run on less than 97/98 RON

andygriff wrote: sleeper wrote: M52's have knock sensors too. the maps will adjust for fuel grade between 94 & 98 dependent on the knock signal. 91 - 98 RON on later BM's ! As you say, mapping is availible for a variation of fuel qualitys via knock detection.

You are right the engine knock detector will adjust for fuel quality. However all this will do is advance or retard the ignition. It will not remap the car to suit the fuel. In order to get the most benefit out of hight octane fuel your car ECU needs to be specifically mapped. If your car comes as standard like this then fine but if it is mapped for 95 then you will get little if any benefit from using 98 RON even if your car has a knock sensor.

sleeper wrote: M52's have knock sensors too. the maps will adjust for fuel grade between 94 & 98 dependent on the knock signal.

91 - 98 RON on later BM's !

As you say, mapping is availible for a variation of fuel qualitys via knock detection.

johnsher wrote: bmw325tds wrote: Running 98 or 97 won't make any difference unless your car is mapped to suit. well as he has a 2003 330ci then it is and the manual explicitly says to use 98 rather than anything else.

If it says in the manual the car should be run on 97/98 then it is the best fuel to use. However that doesn't mean you will feel a noticable difference either in your pocket or on the road

really?

I remember being corrected on that point once:

The tanks only go from full to half empty before refilling by tanker as this eliminates sediment & condensation and allows for 'emergency supplies' in the event of a national emergency etc.

hmmmm.

I'll be the spanner in the works then!

I think that optimax does make my car run better.

I had to use texaco (sorry - could be anything!) 95 on sunday and it was cr@p. back on the good stuff now AND the performance is improving as the probe pics it up.

psychological? maybe...

Peter Fenwick wrote: I spent quite a lot of time when I first got my car comparing the performance and economy when using Optimax and standard UL (I even did a graph in Microsoft Excel! Very sad I know). Optimax gave only slightly better economy and I didn't notice any improvement in performance. IMO it's not worth the extra cash and unless your car is specifically set up to run on it I wouldn't bother.

wow that's dedication!  Setting up a graph.  Can't say I've noticed any performance difference either.  But it certainly doesn't do it any harm.  are they not supposed to have cleaning agents in them as well?  Optimax that is.