BP's 95 RON vs Shell 98 (Optimax)

[Tripps]

I had to fill up at a non-Shell station last week so thought I might as well rough-it and try their 95 RON stuff rather than the posher 97 stuff to see how the car runs on it.

Duly filled up with 62 litres or so and switched the RR button to 95 mode - since then its been popiing and banging like never before.

Is it the fuel, the RR setting or just me going mad?

I haven't noticed any performance differences as yet, but saying that I haven't pushed it since to be really sure.

[beano500]

My logic may be faulty, but....


If you still had some superduper in the bottom of the tank and then hit the 95 button.....???

[Tripps]

beano500 said:

My logic may be faulty, but.... If you still had some superduper in the bottom of the tank and then hit the 95 button.....???

I had thought of that, but my top-up was 62 litres, so that would have splashed down into the three litres in the tank and mix up with it, so just less than 5% of the tank contents would be Optimax which I can't see having a big affect.

Although the first few few hundred years or whatever would have been pure Optimax in the pipes and pump...

[mark.rowe]

Could be that the lower quality 95 ron is not fully burning as good as the 97 in the cylinders and carrying over into the exhaust giving more pops and bangs?

I'm an engineer on ships and if we get poor quality fuel (regular occurance!!!) we have a lot of trouble with afterburning.

[Tripps]

mark.rowe said:

Could be that the lower quality 95 ron is not fully burning as good as the 97 in the cylinders and carrying over into the exhaust giving more pops and bangs? I'm an engineer on ships and if we get poor quality fuel (regular occurance!!!) we have a lot of trouble with afterburning.

Jeez, pop and bang on a vessels like that must be something

Hmm, that's a good point, although I'd hope that BP fuel should be good enough though? A standard 4.5 on 95 pinks because of underfueling though doesn't it? So perhaps pressing the RR button causes over-fuelling compared to the 97 setting...

I've always found 95 Shell to be better than the 95 from petrol stations so whatever additives or refining process Shell use could be the issue.

I recall once filling a jerry can with Supermarket petrol and spilling it when withdrawing, the petrol evaporated quickly, leaving a powdery deposit.

[mark.rowe]

Pops and bangs on a vessel!!

That would be fun!!
What happens is the afterburning causes a higher temp in the cylinder and ext outlet. The fuel we use is residual heavy oil. The problem occurs if the fuel has a high vanadium content which melts at the higher temps then welds itself onto the exhaust valves! rsulting in a bloody work up changeing valves when I should be out on deck working on my suntan!!

[peterrosey]

The lower the octane rating the more likely the fuel is to detonate - sounds like a little unburnt fuel is burning off on the over-run hence more pops and bangs.
Most people think that the higher octance fuel burns faster and is easier to ignite, but it's actually the other way around.

[Tripps]

peterrosey said:

The lower the octane rating the more likely the fuel is to detonate - sounds like a little unburnt fuel is burning off on the over-run hence more pops and bangs. Most people think that the higher octance fuel burns faster and is easier to ignite, but it's actually the other way around.

That makes sense, that derv stuff ignites quicker too.

Don't Americans use something silly like 85 RON - quite fancy trying some of that now through a long Alpine tunnel

[Rob Dance]

`scuse my ignorance, but what / where is this "RR" button.

I am presuming it is part of the car rather than a metaphorical item ??

[J_S_G]

Rob Dance said:

`scuse my ignorance, but what / where is this "RR" button. I am presuming it is part of the car rather than a metaphorical item ??

You only get it on the 4.5RR. It's to the left of the steering column, near the cigarette lighter/ashtray/air-con as far as I can remember (geeze, I'm starting to forget what the interior of a Cerb looks like ).

[Tripps]

J_S_G said:

Rob Dance said: `scuse my ignorance, but what / where is this "RR" button. I am presuming it is part of the car rather than a metaphorical item ?? You only get it on the 4.5RR. It's to the left of the steering column, near the cigarette lighter/ashtray/air-con as far as I can remember (geeze, I'm starting to forget what the interior of a Cerb looks like ).

On the left side of the stereo, on the "column" around the dash centre.

It has 97 at the top and 95 on the bottom, or "go fast" and "go not quite so fast" as I like to see it

I'm told it changes the ignition advance, but as my manual mentions nothing of it I base that purely on heresay!

[SXS]

Its a gimmick... doesnt do nothing... like the aircon... hehe

[beano500]

Tripps said:

Don't Americans use something silly like 85 RON - quite fancy trying some of that now through a long Alpine tunnel

I think there was a very informative thread not so long ago about RON and MON and from that and following a few links I deduced that, as so often in America, they're on a different scale.