Super Unleaded
Discussion
Picked up my new toy this week. It needs super unleaded, or at least I think it does.
In the book, for the lesser models in the range, it states "premium unleaded min 95 RON". For the engine varient I have it states "super unleaded min 95 RON". Err, thats the same octane rating then. Does it really need super unleaded?
I did notice there was a difference in minimum MON levels (cannot remember what the figures were now). Would that account for needing the super?
Assuming that it does indeed need it, I noticed on the way to work this morning that no garages I passed had the price of super advertised on the big board that can be seen from the road, even though I know most of those garages do (or at least did) sell super. Is the price of super normaly a fixed amount more than unleaded, or is it similar to diesel, or is there any other way of guessing how much it will be, or is it a matter of either pot luck or driving onto the forecourt to have a look at the price on the pump?
In the book, for the lesser models in the range, it states "premium unleaded min 95 RON". For the engine varient I have it states "super unleaded min 95 RON". Err, thats the same octane rating then. Does it really need super unleaded?
I did notice there was a difference in minimum MON levels (cannot remember what the figures were now). Would that account for needing the super?
Assuming that it does indeed need it, I noticed on the way to work this morning that no garages I passed had the price of super advertised on the big board that can be seen from the road, even though I know most of those garages do (or at least did) sell super. Is the price of super normaly a fixed amount more than unleaded, or is it similar to diesel, or is there any other way of guessing how much it will be, or is it a matter of either pot luck or driving onto the forecourt to have a look at the price on the pump?
I think super is 97RON or above, thats what it states for my car.
Tesco Momentum is 99 Ron.
So, chances are you will be fine on standard unleaded. BTW, I have never come accross a garage that doesnt have super unleaded but then I only use V Power or Momentum.
What car are you talking about?
Tesco Momentum is 99 Ron.
So, chances are you will be fine on standard unleaded. BTW, I have never come accross a garage that doesnt have super unleaded but then I only use V Power or Momentum.
What car are you talking about?
The last owner reckoned it was both more economical and more responsive on super.
As the book implies that it should be using it, I think I will do. I am sure there will be the odd occasion when I cannot get super, and they will be the days that I experiment.
Not had a chance to drive it much yet, but first impresions are very good.
As the book implies that it should be using it, I think I will do. I am sure there will be the odd occasion when I cannot get super, and they will be the days that I experiment.
Not had a chance to drive it much yet, but first impresions are very good.
No idea what the deal is with the Smart ECU, but this old post I wrote may help with explaining the difference between super and normal unleaded. Perhaps with this knowledge and a bit of digging on the features and fuctions of your car's ECU you'll be able to work out if super unleaded will help.
OK, quite a lot of concepts to cover here, I'll try and hit 'em one by in one in some kind of sensible order. The answer to your question will be right at the bottom! There is a lot of twaddle written about super unleaded. Manufacturer's seem to like to promote the idea that it has more "go". That's not strictly true.
RON refers to the Research Octane Number of the fuel. It measures the highest useable compression ratio of the fuel before detonation occurs.
In the UK, standard unleaded must have RON>=95 and Super unleaded >=97 if I remember correctly.
Detonation is the self ignition of the air fuel mixture in the cylinder due to heat and compression. Detonation is bad. Detonation should be thought of as an explosion, all the energy of the fuel is released in a very short period of time. There is a massive shock to the engine and a collosal release of heat. Detonation WILL hole or melt your pistons.
What should be happening in the engine is a controlled burn of the air fuel mixture.
There are a couple of ways of stopping detonation.
1/ Reduce the running temperature of the cylinder.
2/ Drop the compression ratio of the engine (the maximum cylinder volume divided by the minimum cylinder volume)
3/ Enrichen the mixture.
4/ Start the controlled burn of the fuel a little before the piston reaches top dead centre.
5/ Increase the resistance of the fuel to detonation.
Obviously, without major engine mods we cannot change 1/ and 2/.
Enrichening the mixture means decreasing the air to fuel ratio, but you get the most power from petrol with a 14.7:1 ratio. Increasing this ratio will decrease power AND pour unburnt fuel straight out of the exhaust pipe. Not a good solution - although a richer mixture will have more detonation resistance.
Looking at 4/ the idea here is to allow the flame front to propagate from the spark plug to all the nasty hotspots where detonation may occur in the cylinder BEFORE the pressure (and therefore temperature) rises to such a high level that detonation actually begins. Once the mixture is already burning, detonation cannot occur.
This is ignition retard. Firing the plug before the cylinder reaches the end of the compression stroke.
Unfortunately, if we start the burn before the cylinder reaches the top of it's cycle, we are exerting a force on the piston that slows it down. As well as this, we've expended fuel on the compression cycle that could have been used on the expansion cycle. Result, less power.
So ignition retard is a double edged sword. It stops the engine melting, but it costs us power.
Some modern cars have knock sensors. These sensors are mounted into the block and detect the shockwave generated as the air fuel mixture begins to detonate. The ECU notes that detonation is beginning to occur and reatards the ignition a little further. Such a system keeps the car just on the edge of detonation - meaning the engine is producing the maximum safe power.
OK, how about 5/ ?
Increasing the resistance of a fuel to detonation will allow you to run at a higher temperature, a higher compression ratio or less ignition advance. Or a little of each.
Super Unleaded has a higher resistance to detonation than Unleaded. Unfortunately IT DOES NOT contain more energy.
If you put super in a car that has a knock sensor, it will run more efficiently, and produce more power. This is becasue the ECU will detect that detonation is not occuring and deduce that less igntion retard is needed. Less ignition retard = more power.
Unfortunately, if you put Super in a car that isn't able to dynamically adjust ignition timing to reduce knock, the ECU has no way of knowing that the fuel you've fed it is superior in any way. It will just keep the factory ignition map. The extra detonation resistance of the fuel is wasted and the car will perform no differently that it would if you fed it standard unleaded.
The other alternative is that your car has been tuned to only use super. In this case the ignition timing has been advanced to fire the spark just before knock is noticable with super unleaded. This will be later in the cycle than with normal unleaded. The ECU is not smart enough to reduce ignition advance when it see's knock, so normal unleaded will cause problems in this setup.
This is how some tuners tweak more bhp out of a standard engine. Feed it super and remap it. Downside - you're stuck with super.
If you believe the oil giants, there are other benefits to super unleaded. They will tell you that it also has superior cleaning properties. It probably does, but I'm not sure it'll make any difference.
And finally.
RON 95 means that the fuel performs as well as a fuel mixed from 95 parts Iso-octane and five parts n-heptane. Iso-octane and n-heptane are reference fuels picked fairly arbirarily.
There are actually three standards, RON, MON and the average.
Research Octane Number is measured in a real engine with variable compression ratio; the ratio is increased until knocking is detected and it is compared with reference blends of iso-octane and n-heptane to see which one it matches.
MON = Motor Octane Number and is also tested in a real engine in the same way as above. HOWEVER, the RON test is carried out with variable ignition timing but the MON test is carried out with fixed ignition timing. in this way the MON test is always more severe than the RON test so a given fuel will have a MON and a RON and the MON<RON.
In the UK, Europe and Japan the quoted octane number is always RON. In the USA they always quote the average of ROM and MON, sometimes called the anti-knock index (AKI) or shown as (R+M)/2. Hence why US-quoted 'octane numbers' are always lower than UK ones, even though the fuel may be of equivalent knock resistance.
OK, quite a lot of concepts to cover here, I'll try and hit 'em one by in one in some kind of sensible order. The answer to your question will be right at the bottom! There is a lot of twaddle written about super unleaded. Manufacturer's seem to like to promote the idea that it has more "go". That's not strictly true.
RON refers to the Research Octane Number of the fuel. It measures the highest useable compression ratio of the fuel before detonation occurs.
In the UK, standard unleaded must have RON>=95 and Super unleaded >=97 if I remember correctly.
Detonation is the self ignition of the air fuel mixture in the cylinder due to heat and compression. Detonation is bad. Detonation should be thought of as an explosion, all the energy of the fuel is released in a very short period of time. There is a massive shock to the engine and a collosal release of heat. Detonation WILL hole or melt your pistons.
What should be happening in the engine is a controlled burn of the air fuel mixture.
There are a couple of ways of stopping detonation.
1/ Reduce the running temperature of the cylinder.
2/ Drop the compression ratio of the engine (the maximum cylinder volume divided by the minimum cylinder volume)
3/ Enrichen the mixture.
4/ Start the controlled burn of the fuel a little before the piston reaches top dead centre.
5/ Increase the resistance of the fuel to detonation.
Obviously, without major engine mods we cannot change 1/ and 2/.
Enrichening the mixture means decreasing the air to fuel ratio, but you get the most power from petrol with a 14.7:1 ratio. Increasing this ratio will decrease power AND pour unburnt fuel straight out of the exhaust pipe. Not a good solution - although a richer mixture will have more detonation resistance.
Looking at 4/ the idea here is to allow the flame front to propagate from the spark plug to all the nasty hotspots where detonation may occur in the cylinder BEFORE the pressure (and therefore temperature) rises to such a high level that detonation actually begins. Once the mixture is already burning, detonation cannot occur.
This is ignition retard. Firing the plug before the cylinder reaches the end of the compression stroke.
Unfortunately, if we start the burn before the cylinder reaches the top of it's cycle, we are exerting a force on the piston that slows it down. As well as this, we've expended fuel on the compression cycle that could have been used on the expansion cycle. Result, less power.
So ignition retard is a double edged sword. It stops the engine melting, but it costs us power.
Some modern cars have knock sensors. These sensors are mounted into the block and detect the shockwave generated as the air fuel mixture begins to detonate. The ECU notes that detonation is beginning to occur and reatards the ignition a little further. Such a system keeps the car just on the edge of detonation - meaning the engine is producing the maximum safe power.
OK, how about 5/ ?
Increasing the resistance of a fuel to detonation will allow you to run at a higher temperature, a higher compression ratio or less ignition advance. Or a little of each.
Super Unleaded has a higher resistance to detonation than Unleaded. Unfortunately IT DOES NOT contain more energy.
If you put super in a car that has a knock sensor, it will run more efficiently, and produce more power. This is becasue the ECU will detect that detonation is not occuring and deduce that less igntion retard is needed. Less ignition retard = more power.
Unfortunately, if you put Super in a car that isn't able to dynamically adjust ignition timing to reduce knock, the ECU has no way of knowing that the fuel you've fed it is superior in any way. It will just keep the factory ignition map. The extra detonation resistance of the fuel is wasted and the car will perform no differently that it would if you fed it standard unleaded.
The other alternative is that your car has been tuned to only use super. In this case the ignition timing has been advanced to fire the spark just before knock is noticable with super unleaded. This will be later in the cycle than with normal unleaded. The ECU is not smart enough to reduce ignition advance when it see's knock, so normal unleaded will cause problems in this setup.
This is how some tuners tweak more bhp out of a standard engine. Feed it super and remap it. Downside - you're stuck with super.
If you believe the oil giants, there are other benefits to super unleaded. They will tell you that it also has superior cleaning properties. It probably does, but I'm not sure it'll make any difference.
And finally.
RON 95 means that the fuel performs as well as a fuel mixed from 95 parts Iso-octane and five parts n-heptane. Iso-octane and n-heptane are reference fuels picked fairly arbirarily.
There are actually three standards, RON, MON and the average.
Research Octane Number is measured in a real engine with variable compression ratio; the ratio is increased until knocking is detected and it is compared with reference blends of iso-octane and n-heptane to see which one it matches.
MON = Motor Octane Number and is also tested in a real engine in the same way as above. HOWEVER, the RON test is carried out with variable ignition timing but the MON test is carried out with fixed ignition timing. in this way the MON test is always more severe than the RON test so a given fuel will have a MON and a RON and the MON<RON.
In the UK, Europe and Japan the quoted octane number is always RON. In the USA they always quote the average of ROM and MON, sometimes called the anti-knock index (AKI) or shown as (R+M)/2. Hence why US-quoted 'octane numbers' are always lower than UK ones, even though the fuel may be of equivalent knock resistance.
Thank Mike, a lot of useful info there.
This is something that I am sensitive to as my last Subaru died after a melted piston made it uneconomical to repair. The book for that car said that 95 Ron was fine and also that it has a knock sensor. Everyone since has told me I really should have been using super in it.
Obviously, I dont want to destroy another engine in the way. At the same time, if there is no benifit, there is no point in spending the extra fuel money. Since the book implies that I should be using super in the Brabus, I will do. I just wish the prices were advertised better.
This is something that I am sensitive to as my last Subaru died after a melted piston made it uneconomical to repair. The book for that car said that 95 Ron was fine and also that it has a knock sensor. Everyone since has told me I really should have been using super in it.
Obviously, I dont want to destroy another engine in the way. At the same time, if there is no benifit, there is no point in spending the extra fuel money. Since the book implies that I should be using super in the Brabus, I will do. I just wish the prices were advertised better.
Tonberry said:
I stand corrected.Do you live anywhere near modern civilisation?
I've never seen a garage that does not sell Super.
Op, I've found recently that Tesco premium fuel seems to be the cheapest premium. There is no real way of telling the price until you get to the pump unfortunately. It fluctuates quite a lot tbh, well here anyway. Shell is worst for this, it went from something like 5p extra to 9p extra in a fortnight. I always use high octane providing its available as my suzukis handbook tell me to.
Tonberry said:
Marf said:
LuS1fer said:
Tonberry said:
All garages sell Super.
Not all. I stand corrected.Do you live anywhere near modern civilisation?
I've never seen a garage that does not sell Super.
It's rather annoying a a) they're about 0.5 miles from me and b)their V-Power was usually 3ppl cheaper than the next nearest Shell station.
Caulkhead said:
It's a turbocharged petrol engine producing more than 100bhp/litre then. Even if it doesn't have to have super, there's a good chance it will benefit from the higher octane. I'd go with super.
No it wont at all. Only if its mapped to run on Super.For instance our R53 Mini Cooper S John Cooper Works said it was to be run on Super because it was mapped for it.
On a diesel Bio Diesel has a higher cetane value than regular diesel. Using your theory it would benefit a diesel car to run on it
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