Premium unleaded - worth it?

Lum

A._Badger wrote: »

If these mystery additives (which are never specified, you can't help noticing) actually did anything provable, the very same marketing departments that are trying to persuade the gullible to buy 'premium' fuels, would be turning their guns full on the supermarkets. So would the car makers themselves. And both would do so using claims that stood up to scrutiny.

I used to have a "Knock Link" external knock sensor on my old Subaru Legacy B4 RSK after I killed one engine due to the previous owner running it on standard unleaded (and claiming to have had it remapped when it later transpired that the JECS ECU on the 1999 model was not re-mappable) and me running it on 97 RON BP Ultimate.

Basically if driving hard enough, and on crappy enough fuel, to cause detonation, I'd get a series of warning lights, with orange meaning to back off and red meaning you may well be doing damage.

With 99RON Shell V-Power in there I didn't have to worry about how hard I drove the car (once it was warmed up, obviously), the worst I ever got was the first orange light flickering at around the point that the second turbo kicked in.

With 97RON BP Ultimate I had to be a little more careful, and not just blindly plant my foot to the floor.

On 95RON flooring it simply wasn't an option, it'd get me a red light pretty much every time.


Now the thing to bear in mind is this car was a Japanese import, mapped for 100RON, and has a bit of a reputation, even amongst Japanese owners, of having a design that was pushing it a bit. Subaru tinkered and fiddled with the twin-turbo setup every model year before eventually giving up and going back to single turbo with the BP/BL models.

If you're driving a Corsa or Focus or something all this is going to be a complete non-issue for you, I'm only posting it to point out that there is a difference in the fuels, something that I measured with an actual measuring device rather than the butt dyno.

A._Badger

Lum wrote: »

If you're driving a Corsa or Focus or something all this is going to be a complete non-issue for you, I'm only posting it to point out that there is a difference in the fuels, something that I measured with an actual measuring device rather than the butt dyno.

A very interesting comment, thank you. Obviously, as you say, there is a difference in octane and it is measurable. It's also relevant if you have an engine than demands a higher octane (though my import Eunos Roadster seems to run well on basic fuel, it's not a very stressed engine).

I suspect the problem here is that there is a confusion in some people's minds as to the difference between octane and additives - which cars need the former and whether the latter are relevant.

Lum

A._Badger wrote: »

A very interesting comment, thank you. Obviously, as you say, there is a difference in octane and it is measurable. It's also relevant if you have an engine than demands a higher octane (though my import Eunos Roadster seems to run well on basic fuel, it's not a very stressed engine).

Your MX-5 is not turbocharged. Once you do that, that is when octane ratings really start to matter.

almillar

Let's separate a few things out here:
Marketing guff - BP Ultimate, Shell V-Power etc - ignore these, pay attention to the RON rating - standard unleaded is 95, premium is 97/98 and Tesco Ultimate is even higher. Those numbers are specifications, and real. If they didn't work when you filled your Ka's tank, fair enough, but there IS a real difference.
As has been said several times, check your manual. It tells you what grade if fuel to put in. In general, American cars have to run on 91 RON, and Japanese on 97 as examples. Some engines can adjust between these types. Of course, it doesn't happen instantly, you'll need to flush through the old stuff, then reset the ECU, for it to 're-trim' to the new stuff.
Or if you've imported a car from Japan, you may be stuck with 97 RON, and might damage the engine if you put 95 into it.
Or maybe your car's been tuned and it'll only take 97.
I had an RX8, which basically had the ECU locked per country (or continent at least). Same engine. Power in America was 220bhp, in UK was 230, and Japan was 235. This reflects the real differences that premium unleaded gives. There was no point in me putting premium in my RX8, since it had been 'hard wired' to 95 RON.
So check your car's specs instead of spouting off a 1 tank test you did.

Lum

almillar wrote: »

As has been said several times, check your manual. It tells you what grade if fuel to put in. In general, American cars have to run on 91 RON, and Japanese on 97 as examples. Some engines can adjust between these types. Of course, it doesn't happen instantly, you'll need to flush through the old stuff, then reset the ECU, for it to 're-trim' to the new stuff.
Or if you've imported a car from Japan, you may be stuck with 97 RON, and might damage the engine if you put 95 into it.

Pretty accurate, but a couple of points.

America don't use the RON rating, they use PON, which is the average of the RON and MON ratings. It's hard to convert exactly but as a rule of thumb American "standard" 89 is about 93 RON and American "premium" 91 is about 95 RON. This is also why regular UK unleaded is called "premium". You can actually get 93 in America, equivalent to our "super" 97 RON, but this is rare and no unmodified American car is going to require this.

So in general if you drive an American import, you can run it on any old crap in the UK.

In Japan, their standard is 98RON and their super is 100RON. A lot of their performance cars will adapt to both, but not all, so be careful. Even if you've imported a non-turbo Japanese car (e.g. Toyota Previa, Mazda Bongo, Honda Beat) it may be necessary to run it on super or get it remapped as the ECU programmers may not have written it to cope with 95. Check on the owners forums if unsure.

iolanthe07

and £143 for the "posh stuff",
If this is per litre, you've been robbed!

fivetide

Lum wrote: »

Even if you've imported a non-turbo Japanese car (e.g. Toyota Previa, Mazda Bongo, Honda Beat) it may be necessary to run it on super or get it remapped as the ECU programmers may not have written it to cope with 95.

I'd be a lot less concerned about a family motor that isn't going to be driven hard than a fire spitting turbo though. I would suspect failures are few and far between for this.

Even the FTO I had ran fine on 95. On a slightly related note to some comments further up the thread, as it was an auto I wouldn't have wanted to pull the fuses all the time either as this screwed the gearbox up something chronic. It would learn your driving style so any battery disconnection (30 mins I believe for the codes to all clear) would give some rather weird gear changes. Pulling a fuse isn't as quick or simple as it appears.


EDIT to add in:

Think this has seen any V-Power in the last half a million miles? "Never had a serious breakdown"

http://www.bbc.co.uk/news/magazine-18910560

5t.

Lum

This is why I stated "may" I don't have any first hand experience with non-turbo Japanese imports.

Owners of such cars should check before driving hard on 95, that is all.

fivetide

Lum wrote: »

This is why I stated "may" I don't have any first hand experience with non-turbo Japanese imports.

Owners of such cars should check before driving hard on 95, that is all.

No worries. Just came over a bit scarey is all.

I've had a few, even performance ones like the FTO (had the 3.0 non-turbo Supra as well) and absolutely no issues with 95 petrol.

The Subarus though - different matter.

5t.

red_eye

Rory2000 wrote: »

Hi,

IMHO there is no use in this petrol unless you are using a car with a big engine i.e it uses a lot more fuel , i had a company car which i put 40,000kms on it from new toyota corolla 1.8 petrol and tracked all the fuel that went into it, the higher octain fuel does go further but when i workied back the cost it was still cheaper to use normal unleaded.

not entity true, higher ron rating= less prone to heat ignition this allows the engine to retard the ignition with out the air/fuel mix detonating early and ultimately detonating your engine (shockwave of the expanding gasses hitting the piston (knock))

the more you can delay the ignition the more you can compress the air/fuel (normal engines ignites the fuel before the piston reaches top dead center (TDC) say 20degrees, this gives the flame time to fill the combustion chamber readt to push the piston down as it goes past TDC (not 100% of the energy is used to push the piston some of it used to fill the chamber). compress the mix more and ignite at say 5 degrees and the flame front expands quicker more of the energy is used on the piston. this will give better performance and ecconomy

so yes useless in all engines with out the proper ignition map unless it has a dizzy then you just loosen and rotate clockwise a little