Where do you usually get your fuel?

For a good while I've been running an M3 on Optimax, as you do, but last week I found myself having to fill up at a BP station.

There seems to be a slight change in the car while running on BP Ultimate, it seems to idle and rev a lot 'smoother' through the middle of the revs but also seems to have a little less power at the top of the rev range.

I'm back firmly on Optimax again now for the foreseeable future, but wondered if anyone else has experienced similar things or used any different fuel like Esso (or whoever else makes premium over 96RON)........

What car have you got Mr G?

Reason for asking is that the E36 M3's have kock sensors which should allow you to run higher octane fuel and feel the benefits from it...... but also allow lower grade fuels without the problems of 'Pinking' under load.

The E30's have no knock sensors, but I remember seeing a thread recently which highlighted connecting various combinations of connectors near the ECU depending upon which grade of fuel you prefer.

Hope this helps.

Jonners wrote: am confused on this some say no point in running higher octane if the car is properly set up for 95 octane but no matter how the engine is tuned surely a higher calorific value fuel will be better or perhaps if the 98 octane burns differently then it won't suit the ignition timing set up for 95 octane can anyone explain?? the theory seems to conflict with people's experiences - or maybe there's a psychological factor at work...

As far as I understand it it goes like this. A higher octane fuel allows for a more advanced ignition or a higher compression ratio before knock occurs. This alone gives the increase in power, not the fuel. So if your car doesn't have knock sensors (allowing it to alter ignition timing depending on the fuel) and you haven't raised the comp ratio then it won't make any difference what fuel you use (as long as its not diesel!).

I have also heard that using higher octane fuel alone can actually slightly reduce power as it has a lower calorific value?!

UweM3 wrote: BMG M3 wrote: Reading this months Evo mag's Q&A page, it says..... " most modern engine management systems can sense the fuel RON and advance the ignition timing to make the most of it" yes but only to a given range. Is there anywhere in Europe fuel available from petrol stations with more than 98 Octane? (don't say Shell V-power now, that's only available in Germany and only since last year).

Well, there's supposed to be Tesco's experimental 99RON super unleaded - only available from a few outlets.

There's also proper leaded 4-star, which is 99.6RON.

We sell proper leaded 4 star where I work, but it will kill your cats!

When I was working for a Rover dealer back in 1990, I went on a course for engine management and ignition systems. Thier Mems systems all had knock sensors. BUT, thier systems constantly wound the ignition advanced untill it detected pinking, then back off a few degress, then after a few seconds, advance it again. Mind you, it lead to plenty of burnt out valves and head gasket failures on the old A series (Maestro) and O' series (Meastro/Montego/boxy 216) and M' series (820,220,420) Funily enough, none of the Honda engined Rovers ever suffered from that!

Before mapping cars, I make sure the customer fills the car up with the fuel they are going to be using everyday, especially when they want the "max" out of the engine. Agressively tuning the engine with Optimax then the driver putting in 95 octane fuel may do damage to the engine, even with an knock sensor, as they only retard to a limit too.

But, I agree with Uwe, a higher octane fuel won't really make your knock sensor tell the ECU to advance up the ignition, its only used for "safety" incase the quality of fuel is poor for some reason.

SHEPSM3 wrote: We sell proper leaded 4 star where I work, but it will kill your cats!

My car's so old, it doesn't have any cats!

Horsetan wrote: My car's so old, it doesn't have any cats!

 You are lucky!

95 E36 M3.0

I have a factory sticker in the corner of the windscreen stating 98 RON or over. Optimax is 97.....!?

I know that the octane rating differs over the world and has something to do with combustion temperatures (i.e. US gas is rated something like 88 but is equivalent to uk unleaded, 93-5)

How much... roughly?

Just checked the shell website and V power was developed with high levels of detergent in the fuel mixture to help remove carbon deposits from the valves. The side effect is a high octane rating. It's available in the US too.

Optimax is 98 RON. The handbook for the E46 M3 also states to use 98Ron where possible although the car can be run on 95 if need be.

Going back to the orginal question, When I had my old car (mitsi FTO) It actually seemed to prefer the 97 BP Super, seemed smoother somehow. I haven't noticed any difference between BP and optimax in the M3 so I stick to opti as its at the recommeded RON as is usually cheaper than BP where I live too.

Just for info, the Japanese have 100Ron fuel which the FTO was set up for and that worked fine on any grade/make of petrol. Even Jet!

///Mister_G wrote: I have a factory sticker in the corner of the windscreen stating 98 RON or over. Optimax is 97.....!?

I have just put £10 of Shell regular in a virtually empty tank as a bit of an experiment.....

...A few miles back to the office and performance seems (very)slightly affected but my consumption seems to have risen dramatically?!?!?!?!

I reset the obc at every pitstop, and I usually see somewhere between 20 - 25mpg which is raised by 20 miles of motorway to around 30mpg.

Consumption today without motorway = 32mpg!!! (with standard throttle control behaviour)

Very strange........ but no complaints!!!

my m3 evo has got a sticker on the petrol gauge stating 98 ron so ive only used optimax in it for past 18 months since i bought it, fuel consumption seems good around 25mpg around town and about 31 mpg on motorway.

Experiment results

Car ignition failed to catch first time on two occasions from cold start which has never happened before. Everything else is fine.

I won't be trying this experiment again and duely treated the beast to £60 of optimax this morning.