Petrol !

[JNC]

I have up graded my Duratec to RBTB's and am now going to the Two Steve's for Tuning and Dyno  to optimism my car. One thing Steve asked was what fuel was I using ? Standard or high octane as it makes a difference to setup , I'm using standard at the moment . What are your thoughts. Also he doesn't rate Shell Max. What are you using ?

[DJ.]

For a road car, I would definitely get it set up on 95 octane fuel, as there are places you might like to visit (ie, Scotland) where it is hard enough to find 95 let alone 97 or higher.

I'm sure you'll get more power if you set up on higher octane, so if it's mainly a track car, use that.

[ECR]

My (track) car is mapped for 95. It is always available whereas 98 often requires a drive into the countryside to locate which is the last thing I want to do on a track day. If your car is mapped for 95, the difference in power to 98 will be real but minimal. Ask Steve what the likely difference will be ...

[Tom_Arundel]

The octane number (RON) 95 - 98 is a measure of the fuel`s anti detonation properties. This is mostly the flame propagation speed across the combustion chamber at a particular compression ratio. The higher the number the lower the propagation speed /.risk of detonation/ knock

Higher numbers require more ignition advance and /or higher compression ratio to work best.

Back in the old days in F1 going from 4 star to 5 star(higher octane) without any engine changes LOST 10 bhp ! 

As the man said...set the engine up for what you are going to use, 95 is safe

[Wrightpayne]

In the seven i couldn't tell any difference - in the Impreza PPP super every time!!

Ian

[JAL]

I watched this the other day.

Buds

[Steve_K]

While octane number relates to anti-knock, the star rating really relates to the delay period between the spark and the start of the pressure rise. Higher the star, the shorter the delay. I don't think the distinction makes a lot of difference when it comes down to it.

Steve

[OliverSedlacek]

Some engines respond more to high octane fuels than others. These engines are generally designed to run on high octane fuel in the first place and the ECU then de-tunes if it senses that the engine is knocking. My tintop is a good example that produces noticeably more power on the high octane stuff.

If your ECU doesn't have a knock sensor and the software to de-tune the engine, you need to pick a fuel and stick to it.

If an engine wasn't designed to exploit the benefits of high octane fuel in the first place, then you just wont see the benefits. Typically in this respect the most significant factor is compression ratio. Without trying both fuels, you are probably guessing whether your engine sees any benefit.

I'd go for 95 octane myself.

[prangerman]

I recall that the handbook for my K Series is clear that Ron98 should be used in the R300. Peter

[TomB]

I seem to recall that in the manual for my 1996 K series too!

[Slipper man]

The R500K was originally mapped for 95 RON fuel. I kept it that way because a) 95 is easier to find and b) when on track I can put in 98 RON and have a safety margin. Steve seemed to think that was logical.

[JNC]

@ Oliver my engine was designed with a plenum chamber not RBTB's or high lift cams ! So the spec has changed ,  A friend had his done at the two Steves they found much higher compression than normal after his upgrade and have recommended shielded plugs !. This afternoon I have filled up with  bp ultimate and although not noticeably faster the car felt smoother . 

[Colin Cooper]

I have also been advised to use 97 octane fuel in my standard 2ltr Zetec, on carbs. This was not for the extra power output, but it was thought to be a cleaner burn, and better for the engine in general.

Any thoughts?

Col

[Jonathan Kay]

Fifth Gear Fuel test

Not bad for a TV programme. But:

1. The rolling road tests should have been done blinded, and it wouldn't have been hard.
2. As 4 runs were done with each fuel it would have been trivial to test for significance of changes in power output between fuels using with the within-fuel between-run variance.
3. Don't know if they randomised the sequence or controlled for eg inlet air temperature in any other way.
4. Between-lot variation of fuel wasn't studied and might be quite a large effect.
5. The track test was probably pointless without blinding.

Jonathan

[Jonathan Kay]

Deterioration on prolonged storage: Lots of anecdotes, chemically plausible. Any good studies? Anyone ever gone back and refilled with the old stuff after getting an engine going with new stuff after a lay up?

Using a higher rated fuel: Point about knock sensing already made. Beyond that no benefit that I've ever seen documented... 

Branded fuels and detergents and other additives: I was brought up with the dogma that the fuels were swapped between suppliers and most branding was just that*. Several decades on things might well be different. Someone who knew a lot about this once described on BlatChat how much crossover there was nowadays and where supermarket fuels actually come from. Does anyone remember that, or know about current practice?

Jonathan

* That was after the disappearance of benzole mixes etc

PS: Rob at Ratrace recommended 97 RON for my rebuilt 1800K with unchanged compression ratio.

[AntonyH]

Interesting fuel test. As JK says, some blinding wouldn't have been difficult and would have been useful.

Additionally they didn't test for fuel consumption, which is another claimed benefit of the posher fuels, nor did they do any long term testing of any fuel. If a particular fuel does have any cleaning effect (or the opposite) you wouldn't expect to notice a difference on a single test using part of a five litre tank, but over time you might see a change in mpg or power output (up or down).

We used to use a certain unnamed supermarket station for both cars because it was near to home and cheap - there were "more reasons" to shop there but that's not important right now. After a few months the Caterham developed a misfire (turns out the spark plugs had gone furry) and the (diesel) Skoda wouldn't settle at tickover, but hunted +/-100rpm or so.

We stopped using that particular forecourt, moving instead to Shell for the most part, and both cars have been fine since.

[DJ.]

As I understand it, the actual petrol is the same for all brands as there are few refineries and it all comes from them. However, it is the additives put in the petrol at the forecourt that makes the difference. In the Telegraph there is a chap who's been answering car questions for years and he always recommends using a proper branded petrol rather than the cheapest supermarket stuff.

[Born2Run]

I know a private hire taxi chap who I have used for years and he has run the same Citroen with same engine for circa 600k miles before major failure, regularly serviced, probably over serviced. Absolutely convinced he gets better mpg out of the higher rated diesel fuel, mainly motorway runs of significant distance daily. He is a sensible sort of guy and does enough millage in a year to know the difference in my view, after all it is his pocket that is directly affected. As for cleaning, it is hard to know if the regular servicing or the fuel is the cleaning method but circa 600k out of a 2l diesel is pretty good going. Bottom end failure killed it in the end.

I tend to use the 97/98 stuff based on the taxi guys knowledge. I do so little millage it does not make a lot of odds in terms of cost. If I get a benefit thats great, if not well the marketing guys win. Can't honestly say I feel a difference in any vehicle when I have put put in 95 or 97 and that applies to all the different types.

I did spot some 99/100 rated fuels in Germany. The guy in the garage made me laugh as he said it was only for Ferraris and Porsches, probably an element of truth in their somewhere in that I suspect he meant high performance engines.

As for aged petrol, lawn mowers seem to run on really old bad smelling stuff perfectly well. I had some really vintage year old juice I put in. It had that old smell and I am not even sure it was not 2x as it had been in my dads shed since I could remember. Sealed container. So whilst I know it goes off a lot has to do with what engine you need to put it in. 

[Jonathan Kay]

He is a sensible sort of guy and does enough millage in a year to know the difference in my view, after all it is his pocket that is directly affected.

Despite that myths abound in every other area of life that I know and I'd start with assuming that this is no different. If he's doing that many miles with that sort of saving why hasn't he done, or could you persuade him to, run a quantitative comparison?

As for aged petrol, lawn mowers seem to run on really old bad smelling stuff perfectly well. I had some really vintage year old juice I put in. It had that old smell and I am not even sure it was not 2x as it had been in my dads shed since I could remember. Sealed container. So whilst I know it goes off a lot has to do with what engine you need to put it in.

That's also my experience with mowers and boats. Not sure how to confirm the adverse effect of old petrol on starting 7s except for switching back to it immediately after failing with old and succeeding with new.

Jonathan

[Jonathan Kay]

As I understand it, the actual petrol is the same for all brands as there are few refineries and it all comes from them. However, it is the additives put in the petrol at the forecourt that makes the difference. In the Telegraph there is a chap who's been answering car questions for years and he always recommends using a proper branded petrol rather than the cheapest supermarket stuff. 

Honest John? I'm quite impressed with "him" generally but could only find this in correspondence rather than from the writer(s). Surprisingly little from people within the industry, and the additives seem to be added at the yard rather than the forecourt.

Jonathan