Why do people buy high octane petrol?

[mrk]

Nice little OMG rant, but you've missed the point. The reason why I highlighted the fact it was a 318 is not because 'lol its so teh slow, of course you are wrong' but because I cannot for the life of me understand why a 318i would get 50 miles from a tankful more with SUL when my experience has shown that a Z4 3.0i, 530i and a 335i don't get anything like 50 more miles per tank from super unleaded! These are more powerful cars from the same generation (and newer even) which *are* designed to take advantage of higher RON fuel and even they don't deliver the differences you seem to find with yours?

If I was able to gain even more MPG to annoy MarkDavis with don't you think I'd have jumped at it?

Well none of those engines are the same so...

The only way I can show you any evidence really is a side by side drive from a tank of vpower to a tank of normal, well, the other way round of course but that's the only way. You're welcome to come down one weekend. Oh and at your own expense of course.


Anyway, the most gain I've had is about 50 miles, hence why I said up to. I never considered this to be abnormal or unbelievable. Mainly because that's what I have observed...

 

[[TW]Fox]

Well none of those engines are the same so...

So you think it's likely that BMW designed the engine in the 318i to respond much better to 98 RON fuel than the engine in the 330i in the same range?

Anyway, the most gain I've had is about 50 miles, hence why I said up to. I never considered this to be abnormal or unbelievable. Mainly because that's what I have observed...

I really do think its likely to be concidence. So many things can affect a tank average - noticeable stuff right down to stuff you wouldnt notice like wind direction, etc.

 

[rossk26]

I really do think most of the people who claim to really notice the difference are suffering from placebo effect.

 

[[TW]Fox]

That doesnt mean there is no difference, it just means it isn't a 'WOW I JUST FILLED UP WITH VPOWER AND NOW MY WIFE LOVES ME EVEN MORE' night and day difference like some seem to think.

5ish bhp and 1-2mpg. Anything more requires a vivid imagination or a particularly fussy engine, perhaps with an aggresive map. Which might be something you'd find in an Impreza but not a 318i (Or a 330i mrk!).

But given 400 miles at 30mpg using £1.30 95 costs £78.69 and 400 miles at 31mpg using £1.35 97-99 costs £79.08, you can see why its a bit daft not using Super if thats what the car requires. That whole 1mpg gain pretty much cancels out the 5p a litre average difference!

 

[rossk26]

I will only post my experience and if you don't trust that experience then more loser to you.

Good england that...

 

[Gaygle]

5ish bhp and 1-2mpg. Anything more requires a vivid imagination or a particularly fussy engine, perhaps with an aggresive map. Which might be something you'd find in an Impreza but not a 318i (Or a 330i mrk!).

I disagree. Obviously it depends on the engine, but as i have posted, on an N54 engine 20-30bhp difference is perfectly plausible.

For most cars, particularly NA ones, the difference would be as you say - few MPG's, and a couple of BHP. But this changes when you introduce larger engines with superchargers and larger power. Hell, it changes when you add superchargers to smaller engines with decent outputs.

To blanketly state that the only way someone has achieved more than 5ish bhp on a car other than a fussy/aggressively mapped car is through a vivid imagination is silly.

 

[[TW]Fox]

They don't have 99 RON fuel in the States do they (I genuinelly don't know)? Yet plenty of stock 335i's seem to dyno at 320-330bhp...

I could perhaps see it on a 300bhp twin turbo car but not a 140bhp 2.0 16v. Bet you didnt notice the same on your 330i either!

 

[mrk]

I really do think most of the people who claim to really notice the difference are suffering from placebo effect.

You've said it yourself that you don't exactly drive any other way but to waft from road to road so obviously your driving style won't lend itself to noticing any differences surely?

It can't be a placebo when you can feel a difference in acceleration and throttle response at high revs either, if it was then where is the difference coming from? I'll give an example/ On SUL I approach a roundabout leading into Fareham's dual carriageway stretch and just as I'm joining the exit I plant my foot down, still in 2nd gear, the rev climbs fast from 2000 to 4000 to 5500 approaching 6000 before I think about 3rd gear. It happens smooth and fast but with normal unleaded the response is just a bit slower and pickup just that little bit slower as well, it's not enough to go "WHOAH WHOAH! what just happened?! but it's enough to notice.

If you notice little things then you'll notice something like this as well.

Like I said, I drive the same route 5 times a day, my driving style doesn't change and the only thing that does is the fuel I use every few tanks depending on what's closest at the time.

 

[Gaygle]

They don't have 99 RON fuel in the States do they (I genuinelly don't know)? Yet plenty of stock 335i's seem to dyno at 320-330bhp...

They don't have RON that IIRC, they have AKI. Not sure what the difference is, but from a quick Google, it appears as though 91AKI is equal to 95RON with East Coast states having 94AKI (98 RON). Wiki says that this variation in fuel grades in different states is something to do with the different elevations present in the country.

Like i said before, when i still owned my 330i, i didn't see the point of putting 99 in it as it felt no different and didn't give me any MPG increase which i noticed.

I used the same logic on my 335i - if i can't feel a difference, i will happily use the cheaper fuel and save a few quid - however i genuinely can notice a difference. It just doesn't seem to have as much power on 95, much to my annoyance. I've tested it a couple times and i am positive i can feel a difference.

The dyno graphs seem to support my feelings on this.

I could perhaps see it on a 300bhp twin turbo car but not a 140bhp 2.0 16v. Bet you didnt notice the same on your 330i either!

I am certain a 335i N54 twin turbo will be producing 5-6% less power on 95 RON than 99 RON and will be a car where it makes an appreciable difference as it has the right sort of engine to maximise the benefits of high RON fuel.

However, on a 4 pot 2.0 - i can't see what it has that could take advantage of the different octane levels? It wouldn't produce any more power and i can't see why it would carry it any further, let alone 50miles.

Presumably the only cars that will see an increase in MPG, will also see an appreciable increase in power?

 

[Firestar_3x]

Can't see what's going to be special about a 318 engine nor ecu, it will only have basic control over the engine it's hardly going to be that advanced, it simply doesn't need to be.

I can't see you getting 50miles more out of a tank either I've never got that much more in any turbo or supercharged car (95 vs 98 Ron).

I'd be interested for you to explain the engine management and design of you motor which makes it so worthwhile to run super in.

 

[mrk]

I'd be interested for you to explain the engine management and design of you motor which makes it so worthwhile to run super in.

Really now. I trusted what the maker of my engine stated in the manual, that 98 octane fuel gains the best from the engine. And from what I've seen over the years, their recommendation is correct.

If you want a detailed analysis on the engine setup then ask BMW instead of people on a forum?

Edit*

Before someone pulls the defensive card again, just quit that! I'm more than an accommodating person, if you want proof then anyone is welcome to see the difference at their own expense and time.

 

[[TW]Fox]

You've said it yourself that you don't exactly drive any other way but to waft from road to road so obviously your driving style won't lend itself to noticing any differences surely?

a) I've not said I only ever waft. I wouldnt have a 3 litre engine if I never enjoyed the power of my car - something I do all the time. Don't assume that because my preferred style of Motorway driving is to sit at 70 and relax that I don't enjoy my car off the motorway.

b) If you are driving enthuasiastically then any tank to tank average comparison becomes void as there is no way you can guarantee you used the same throttle openings in the same place etc etc. Infact long trips on the cruise or stready predictable trips are about the only ones you can really make a comparison on, and even then there is so much that can influence it.

Month to month I usually do the same sort of thing - back and forth to and from work and around town. I average 19.5-20mpg every time. For some reason this tank, which is about empty now, I've actually managed 21.4mpg. I've no idea why. The fuel is the same. I think my driving has been the same. Yet there is a difference of almost 1.5mpg. All sorts can affect it!

It can't be a placebo when you can feel a difference in acceleration and throttle response at high revs either, if it was then where is the difference coming from?

I suggest you look up what placebo means - as it absolutely can be!

I'll give an example/ On SUL I approach a roundabout leading into Fareham's dual carriageway stretch and just as I'm joining the exit I plant my foot down, still in 2nd gear, the rev climbs fast from 2000 to 4000 to 5500 approaching 6000 before I think about 3rd gear. It happens smooth and fast but with normal unleaded the response is just a bit slower and pickup just that little bit slower as well, it's not enough to go "WHOAH WHOAH! what just happened?! but it's enough to notice.

We are just going to get into a fight if we carry on. Safe to say I just don't beleive this. Well, I guess I sort of can but it's about degrees of 'notice' really isn't it?

 

[[TW]Fox]

Can't see what's going to be special about a 318 engine nor ecu, it will only have basic control over the engine it's hardly going to be that advanced, it simply doesn't need to be.

I can't see you getting 50miles more out of a tank either I've never got that much more in any turbo or supercharged car (95 vs 98 Ron).

I'd be interested for you to explain the engine management and design of you motor which makes it so worthwhile to run super in.

Really now. I trusted what the maker of my engine stated in the manual, that 98 octane fuel gains the best from the engine. And from what I've seen over the years, their recommendation is correct.

If you want a detailed analysis on the engine setup then ask BMW instead of people on a forum?

I'll step in and support mrk here. Just because it's a 318i doesn't mean it's a bobby basic simple engine. He has an N42B20, which has Valvetronic and is designed for 98 RON fuel - it is the recommended grade for his engine. The nominal performance and economy figures for his engine relate to the use of 98 RON fuel.

This doesn't mean it'll do 50 miles a tank less and be noticeably rougher when accelerating if you dont use 98, mind.

To clarify my position in this thread - an engine designed for 98 RON fuel obviously benefits from using it and will suffer a slight reduction in fuel economy and power if you don't use it. This reduction wont be night and day, but it's enough that it isn't worth the marginal saving in economy.

 

[Firestar_3x]

So you don't know then?

I'm afraid to say you have more than the single variable (fuel) in you trips, lots of things could he making the difference, 50miles over a tank is a huge gain, I've never had that sort of gain even on much more advanced cars (ecu wise) and even when the cars specifically mapped for the fuel in question.

 

[mrk]

I don't know what else to say to you really. My door is wide open, all you have to do is take a trip down south.

Safe to say I just don't beleive this.

What don't you believe, that my car can accelerate smoothly?

 

[[TW]Fox]

I don't know what else to say to you really. My door is wide open, all you have to do is take a trip down south.

This wouldn't acheive anything though would it? You could lend me your car, I could fill it with 95, do 100 miles, fill it with 98, do the same 100 miles, perhaps we'd see a different mpg figure, perhaps we wouldn't, but it would be very difficult to narrow any difference down to one cause. There are just too many variables that will affect it. Everything from a subtle different traffic light sequence one day to different winds, different weather conditions, tyre pressures, traffic, etc etc. It all plays its part. Fuel obviously is part of this mix but alone it isn't enough to account for such a huge different IMHO.

 

[Westyfield2]

You also seem to enjoy using two spaces after full stops, you only need one.

You're meant to use two.

 

[mrk]

Well then that's fine but it only leads to one conclusion, that we agree to disagree.

 

[PeterNem]

You're meant to use two.

Maybe if you learnt to type on a typewriter about 50 years ago

 

[[TW]Fox]

What don't you believe, that my car can accelerate smoothly?

Of course your car can accelerate smoothly. The N42 is a lovely engine. I don't beleive that it accelerates noticeably less smoothly by filling with a different grade of permissable fuel. You'll have a bit less power and use a tad more fuel but there shouldn't be noticeable characteristics like that, or it wouldn't be a permissable grade!

People driving around in bonkers tuned Jap stuff notice a drop in smoothness and running quality with 95 Ron. You and me driving UK market BMW's do not, or should not. We'll just get a bit less power and use a little more fuel.

From your user guide:

$!"

Unleaded fuel
The engine runs only on unleaded pet-
rol, which can also be sulphur-free.
Since the engines have a knock control
function, they can run on different
grades of petrol.
The engine of your BMW is designed to
run on:
> Super Plus/premium plus petrol –
octane number 98 RON.
Run the engine on this petrol by prefer-
ence, in order to achieve rated perform-
ance and petrol consumption.
You can also run the engine on:
> Premium-grade unleaded petrol –
octane number 95 RON.
This fuel is also known as:
DIN EN 228 or Euro-Super.
The minimum grade is:
> Regular-grade unleaded petrol –
octane number 91 RON.

As you can see BMW state the engine will run on a range of fuel grades from 91 to 98, but that to acheive rated performance and consumption you should use 98 Ron. If 95 was going to cause roughness etc then it wouldn't be a permissable grade.