Standard 95 ROn or Super 97?

verityboo

My understanding is that it depends on whether the car engines management system has a knock sensor. If it has then it is to advance the engine timing etc to take advantage of the better fuel

Goldenyears

davetrousers wrote: »

Apparently in the USA their regular is 91 Octane! Can anybody confirm this?

That's about the same as our 95 RON. There are two standard methods for measuring the octane number. They use different test engines. It's not a better or worse method. Just different. Add about 5 to US pump octane numbers for equivalent (European) RON.

Lum

It all comes down to the car as others have said. The higher octane figure reduces the likelihood of pre-ignition (also known as knocking or pinking) which can damage engines. Most modern cars have a knock sensor which automatically de-tunes the engine a little (specifically it reduces the ignition timing) which makes it slightly less efficient but doesn't destroy your engine.

So in theory it's a good idea, but the issue is that your car's ECU may not be programmed to deal with super unleaded, in which case it will only be able to set the advance to a figure that the manufacturer has pre determined to be safe for use with normal unleaded, in which case there will be no difference. This is true for most normal cars sold. Performance oriented turbocharged cars are the ones that really run the risk of pre-ignition as the air coming in from the turbo is much much hotter than in a normal car. It's also particularly important on imported Japanese performance cars as their petrol is 100 RON and the engines are mapped up to run on that exclusively.

Even if you can gain from it, anything that makes a car engine more efficient also tends to increase the performance you can get out of it so any gains you have may be cancelled out by your right foot.

Oh and it's only Shell and Tesco that do 99 RON, everyone else does 97. I'm a little wary of Tesco's since they gain the extra octane rating by adding 5% ethanol to the mix. Since ethanol has a lower energy density than normal petrol you may well not see as much MPG as you'd get from a pure 99 RON petrol. That said it's often much cheaper than Shell V-Power so it may still win on MP£.

its-not-me

I'm going to give it a go tonight. I will empty my tank as much as I can and will re-fuel when I'm running on fumes.

I checked the guide book over the weekend and the engine management system can tell what fuel is being used, and adjusts itself accordingly.

I'll get back with what I find out,

Oh, by the way, I am driving an Astra 1.6, and currently get 400-420 miles to the tank.

Strider590

The fuel is not there as a "performance boost", it's there because the ignition timing on old cars or performance tuned cars would result "detonation" or "pinking" when running on 95ron, which damages the pistons.

Normal cars it makes no difference at all because the ignition system compensates for the different fuel type.

Lum

Strider590 wrote: »

The fuel is not there as a "performance boost", it's there because the ignition timing on old cars or performance tuned cars would result "detonation" or "pinking" when running on 95ron, which damages the pistons.

Normal cars it makes no difference at all because the ignition system compensates for the different fuel type.

Well it can make a difference on normal cars because advancing the ignition timing further tends to make the fuel burn more efficiently, and the super unleaded enables this to happen safely.

You're absolutely right about older cars, but there's not that many left that this applies to as we're talking about stuff designed for 4-star or 5-star here!

It's also worth nothing that many of the super unleaded fuels out there also have improved cleaning / detergent additives that can also make an improvement in performance even in cars that don't understand super unleaded. If you find yourself in this situation some people just run oh cheap stuff 95% of the time, then run 2 or 3 tanks of super, say, once a month to give the engine a bit of a clean.

Of course once you start talking about engine detergents you find yourself in a whole new world of bulls**t and snake oil that could take up a thread on it's own.

its-not-me

OK - well I've filled up with BP Super 97 RON, and here are the details.

44.53L @ 1.269 = £56.51, had I used 'normal' petrol, it would have cost me £53.39, so £3.12 more expesive.

By my calculations I current driving costs me about 12.7 Pence per mile, so to make it worth while (purely on a money basis) I will need to get an extra 25 miles out of the tank.

Of course this figure doesn't take into account the 'extra' cleaning properties of the better quality fuel (I normally use Sainsbury's), but I will try to keep to my normal driving style and speeds.

At least it will give me something to take my mind off Englands shambolic attempts at team spirit and football. :eek:

P

rev_henry

its-not-me wrote: »

OK - well I've filled up with BP Super 97 RON, and here are the details.

44.53L @ 1.269 = £56.51, had I used 'normal' petrol, it would have cost me £53.39, so £3.12 more expesive.

By my calculations I current driving costs me about 12.7 Pence per mile, so to make it worth while (purely on a money basis) I will need to get an extra 25 miles out of the tank.

Of course this figure doesn't take into account the 'extra' cleaning properties of the better quality fuel (I normally use Sainsbury's), but I will try to keep to my normal driving style and speeds.

At least it will give me something to take my mind off Englands shambolic attempts at team spirit and football. :eek:

P

It'll be interesting to see how you get on. What car is this in btw?

its-not-me

rev_henry wrote: »

What car is this in btw?

1.6L 51 Plate Astra, so nothing too flash or powerful

:beer:

spaceboy

its-not-me wrote: »

1.6L 51 Plate Astra, so nothing too flash or powerful

:beer:

I wouldnt bother to be honest. By all means fill it up a couple of times to test the mpg but I'd be surprised if it made a difference.