Fuel what types best

As far as I’ve heard/read/seen, higher octane is specifically and really only to prevent detonation, i.e., the fuel going bang from pressure and heat before the piston passes top dead centre, which is not nice for an engine. The higher octane rating reduces the likelihood of this for chemical reasons and allows tuners to advance the timing to get the cylinder to fire earlier, making more power, without risking the detonation I mentioned.

That’s why it’s relevant to tuners, but irrelevant on factory settings.

If you choose to use it for various other reasons, more power to your elbow, but you’re unlikely to have more power to your right foot…

I don’t know how clever the ND ECU is, but I’d be very impressed to know that it advances the timing to the best possible moment, dependent on fuel. Retarding the timing from a ‘factory normal’ map for poor fuel, perhaps, but advancing on good fuel? That’d be something else entirely.

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Years ago I had Civic Type R’s which ran beautifully on 95 ron fuel (they went like stink actually!), but on the couple of occasions when I filled up with 97 ron fuel they did not like it! They were sluggish, it was as though they were being strangled, they just did not want or need anything other than 95 ron. Dunno why, but there it is.

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It might be that when the Premium unleaded becomes E10 that V power and its cousins comes into its own. E10 is supposed to reduce MPG so the cost benefit equation may be much closer. V power and the like are due to remain E5 after the intro of E10 fuels.

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Even V-Power now is an E5 (5% ethanol) fuel.
Last time (29/2/2020) I put some in one of our cars I noticed the E5 sticker was on that pump…

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V power has been e5 for a good while. Last time I looked the only 100% petrol left was esso’s version of V power. That was a good couple of years ago, they’ve probably gone E5 too

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It seems to be an article of faith that every owner of a car with any sporting pretensions must avoid the fuel mere civilians use and spend at at least a fiver a tank more on fuel with added snake oil . The only time I ever noticed an objective difference was on a Mk 2 Golf GTi which , without fail ran 3 or 4 mpg worse on unleaded compared to super-unleaded, back in the Jurassic era .

Sure, there’s loads of ancedotal evidence about Super this and V Power that but all I will say is that ( Golf apart) I have never , ever noticed even the tiniest difference between bog standard recommended fuel and the reassuringly expensive designer stuff. . Now there may be a difference , but if it is indiscernible in my driving , the only advantage VPower offers is bragging rights about one’s petrolhead status . .

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I can only imagine that Golf [as with a lot of 80’s cars] was supposed to be running on 4 star which was 98 octane

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Surely all fuel sold must satisfy the relevant British Standard, even that sold at Supermarkets.

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Yes it does.
As previous comments.

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How about we get 3 new cars.
Fill one up with Shell V Power.
One on 98 RON.
The other on 95 RON.
ONLY 1 person would know what fuel was in each car so no cheating.
Same mileage each time around a track by say 30 people driving cars A,B and C straight after each other.
Mix and match which car is given to each driver.
Each driver would have the same weight as the fuel goes down.
NO times, just each driver assessment of which fuel was in which car.
I bet the results would be all over the place.
Would you be honestly be able to tell the difference?
I don’t think I could.
But it would be quite an interesting test and result perhaps? :slightly_smiling_face:

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Replaced both our Mk1’s ( 146,000 miles) and our Mk2.5 (a mere 104,000 miles fuel filters last year. Need not have bothered…they were fine on a diet of Tesco/Morrisons fuels…thousands of collective gallons of the stuff.
Mlk1? It could not give a damn what goes in, it runs just the same.
Mk2.5? Not sure really…it seems…to start up better, seems to pull a wee bit better, and seems to offer a wee bit better throttle response on champagne fuels.
BUT…I temper that notion with the fact it’s horrid daily 6 mile round trips to school & baack are over, and when it’s driven at all…its over 50/60 miles…with me giving ity beans often.
Can’t discount the benefits of it’s little Italian tune-ups instead of artery clogging work trips.

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I may be completely wrong but I believed that the ecu in the mk3 on would optimise ignition timing continually for any given combination of engine speed and load up to the point where its close to knock and then repeat the process again. It should therefore be able to extract slightly more power and torque out of the engine using a higher octane fuel. If that fuel also leaves lower deposits when burned it should reduce one of the conditions which contributes to knock in the first place. An engine is more likely to knock at lower rpm with higher load than in a wot situation.
Therefore there is a greater margin of safety for the engine in any given situation with a higher octane fuel.
Most modern era cars eke out high power from lower capacity and even in standard form would embarrass most engines from an earlier era. They also try to run leaner mixtures or cut fuel altogether in the interest of economy. These are all risk factors for knock.

But feel free to correct.

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That sounds like a good strategy until you realise that without preset limits it would mean that the safety of the engine is entirely dependant on the functioning of the knock sensor. Knock sensor fails, engine goes boom regardless.

More likely [imho of course, I don’t know i just hope I sound clever] is that the system works in a similar way to that which you suggest but has an upper limit of expected fuel. E.g. it won’t advance the ignition enough that the only way to stop knock would be to run high grade race fuel. So if you have a 3 grade system like in the US it would be sensible to set the system to only go as far as just below the top grade so that with a faulty knock sensor and the lowest grade fuel the car would pink rather than going full detonation.

This is entirely speculation on my part. All I know for sure is that my mk3 does exactly the same mpg on V power as standard unleaded. A bit of redex in the tank does seem to make a slight improvement however but its not statistically significant.

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The first car I drove solo after passing my test in 1903 was my dad’s Triumph Vitesse . Apart from giving me a crash course in dealing with oversteer , it also highlighted fuel quality . Despite having a modest 100bhp from a two litre six ,and not very high compression ratio , it would pink and run on if asked to consume anything that wasn’t 5 star from a name supplier . So Cleveland Discol was fine , but Thrust and Murco were anything but .

That was ancient history though , and I’ve not heard a car pink since the 70s

Modern engine are miraculous - as a kid 100bhp per litre was a pipedream except for racing cars and high end sports cars . The Elan had 105bhp (reputedly , but actually 90bhp ) from 1600cc , Jack Brabhams ‘66 championship winning Repco Brabham had about 330bhp from a 3 litre V8 and yet a 1litre Ecoboost Ford has 3 cylinders, 1 litre and an easy 125bhp. Yes ,it’;s turbocharged , but look at the first 911Turbo- 85bhp/tonne from a rampant sports car, not a shopping trolley .

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Just read an AAA research report from 2017 in the US which indicates about a 3% improvement in horsepower and torque on a 2015 mk3 using premium instead of regular on a standard car. Not a massive amount but does show that the ecu can accomodate the change.

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Passed your test in 1903 ???
Lets face it, for the difference in cost why wouldn’t you put the better fuel in?

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In general I agree with this. It bears out my own experience.

My first time of using V-Power was with my 1997 Vextra-B. Bought from new it was OK, but after a couple of years of using regular (as I had always done on all cars since the early 1960s) it was a pig, coughing and spluttering at low revs, thinking about pinking, generally unhappy.

It was always serviced by the dealer, and me thinking it was the knock sensor, I asked them to fix it; the mechanic Carl (a really good guy) suggested I use a couple of tankfuls of V-Power because a compression test suggested the engine was clagging up with all the short journeys SWMBO did. The change was almost instant, and the car suddenly became amazingly flexible and smooth to drive, with a propensity to go much too fast on the motorway. Importantly, it also did about 10% more mpg and at the time V-Power was only 8% more expensive, so using it was a no-brainer.

Our NC also shows a small improvement in mpg, about 5% with V-Power compared with the (now) six occasions I’ve had to use regular, and I recover the rest with the Shell driver’s club money back. Our NC also has difficulty in staying below 70mph on the motorway…

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My 1903 reference was an (obviously failed ) attempt at saying I was quite old. Cue tumble weed .

Why would you spend more on ‘better’ fuel if your car doesn’t need it? Isn’t that firmly into “giving a pig a strawberry” territory?

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:joy: :joy: Nice one!

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If it’s a PCP three year car or a company car I would agree with you. If however you are an enthusiast owner of a cherished, long term car I would not.
Similar argument for using cheap no name oil or not waxing paintwork.

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