[Closed] Posh petrol maths help

60/47 = 1.276
48/42 = 1.143

The 95 is cheaper

Or another way, 98ron costs 25% more but only improves mpg by 12%

This would be a lot easier if you calculated your fuel consumption in the same units that you buy it in.

I doubt you're getting a full 45 litres for only £48. It'd be more accurate to work it out based on the £/Litre for 98/95 RON in your area.

What car is it?

Also bear in mind there are many other variables. Different fuels from different brands are not the same, nor are they necessarily the same each day - especially if you fill up at a supermarket.

95 RON petrols are NOT all the same.

I doubt you're getting a full 45 litres for only £48

Doesn't really matter so long as he's putting in the same amount of 95 or 98.

Its a Mito Multiair with 135 bhp from a 1.4 turbo
list mpg is 50mpg combined cycle but i suppose that includes start stop which isnt captured in the dashboard figures ive given

oh and as mentioned they are both filling up from about 1/8th left

Ratio is 7.75mi/£ for 98 and 8.66mi/£ for 95.

Maths says the cheaper is better. Anyone is welcome to shoot down my maths (especially since I can't be arsed to show working..)

Where can I get 95 ron that cheap?

Quick calc says 7.75 miles/£ v's 8.66 miles/$

1.4 turbo

Interesting. Non sporty engine but the ECU will vary boost pressure to take advantage of better petrol. Good stuff.

The better petrol might be better for the environment though? I use fancy diesel - the extra cost isn't quite covered by the extra economy, but the difference is reduced to a few pence per litre - it's worth it for the smoother running, for me.

As I expected really but it isnt too much more to run 98, the problem is i prefer driving it on 98 but i waste most of the miles on motorways so it doesnt really matter. hummmmm.....

Doesn't really matter so long as he's putting in the same amount of 95 or 98.

If it's just based on cost of a fill-up from when the light comes on, then it'll not be accurate.

e.g.

95 RON is £1.319/L, so at 4.546L/gallon and 42mpg you get 14.3p/mile
98 RON is £1.399/L, so 47mpg give you 13.5p/mile

I get a different answer to you. Who's correct?

Of course not but that's the info he's providing. Either way, as I posted, 98 costs 25% more, he's stating 12% more mpg - that's quite a difference.

I like the flying Ox 🙂

to calculate the fuel used accurately you need to fill the car with one type of fuel - run it, then refill it and see how much you used. Obviously switching fuels you need to make sure you flush out and dilute out as much of the other as you can and you also need to allow the ECU to adjust to the new fuel.

One reason you may be finding better performance on the 97ron is the car has set itself up for it so when you drop down to 95ron it is slightly out. Being a turbocharged engine this is probably more significant than on a NA car.

I would also agree that the brand of fuel will affect things more. I prefer Shell fuel and will go out of my way to get it as the car prefers it and I honestly notice better MPG.

Flying Ox... Based on the numbers he's given.. I think you've got your cost/L wrong.

Yup. But [b]titusrider[/b]'s initial figures are guff (sorry dude) so any calculation based on them will be guff too.

It's actually cheaper to run it on V-Power.

TSY, that's what it costs up here for normal Shell and V-Power.

The numbers titusrider gives mean bog standard petrol is £1.067/L and super-unleaded is £1.333/L

Ain't nowhere in the UK selling either of them that cheap or with such a huge price gap between the two.

The difference in price between 95 and 98 Ron you are quoting looks a bit off. Around my way I'm paying £1.36 and £1.44 respectively at the moment which is just under 6% increase for the better stuff. As you are reporting a near 12% improvement in performance WHERE I LIVE it would seem a better bet for you.

My car (clio 197 - non turbo 2.0 lt) prefers the higher RON. Only snag is that it becomes even more fun to drive and my MPG stays the same or even gets worse as I seem to have no self control.

the Shell v-power gives me more mileage, but other types of 98 ron don't for some reason.

The extra smoothness and torque are worth it for me, plus there are suppossed to be less co2 emissions and it is suppossed to clean the engine.

non-turbo 2.0JTS alfa engine here, also works better in a 2.0TS.

my MPG stays the same or even gets worse as I seem to have no self control.

+1 unless motorway driving 🙂

I tend to use Shell petrol myself, I'm led to believe the difference in price between standard 95 Ron and V-power is fixed at 8p per litre regardless of the underlying price of the fuel. So as fuel gets more expensive whatever economy benefit you get from the better fuel is amplified.

For example if you get 10% better fuel economy from V-power now that fuel is so expensive its no longer costing 10% extra to buy the more expensive fuel so you come out ahead.

So its a little bit counter intuitive, as fuel get more expensive its tempting to just buy the cheap fuel but this is exactly when the more expensive fuel makes better sense

are the OP's figures a snap shot from one fill up or averaged over time? There are sooooo many variables you really need to be looking at figures for both fuels averaged over several fill ups. also ignore any data from a few fill ups after changing fuels.

the Shell v-power gives me more mileage, but other types of 98 ron don't for some reason.

V Power isn't just 98 ron. It's 99 for a start, and it also contains various additives to do this and that.

There are sooooo many variables

Yep, you probably need to get someone else to fill the tank so that you don't know what fuel is in there. The testing needs to be done blind, or even double blind.

You'll never win a noble peace prize at this rate. 😆

Dr TSY - awarded the noble peace prize for research into fish finger condiments 2010.

I tend to use Shell petrol myself, I'm led to believe the difference in price between standard 95 Ron and V-power is fixed at 8p per litre regardless of the underlying price of the fuel. So as fuel gets more expensive whatever economy benefit you get from the better fuel is amplified.

Nah, because it used to be 2p a litre different, it's increasing with a %.

the Shell v-power gives me more mileage, but other types of 98 ron don't for some reason.

I was told by a petrolhead mate that it goes off after a while; so if you buy high octane fuel from an unpopular station, there's a chance that you're not getting the full benefit. This is word-of-mouth information so could be horse-poo, but he's usually a reliable source.

My own personal experience was on the bike (as I've driven diesels for ages now). I found that putting in a tankful of rocketfuel gave better performance, but that the benefit stayed for a couple of fills afterwards. So, I used to fill up with the power stuff every third or fourth tankful.

there's no reason why higher ron fuel should give you more mpg. it doesn't have any more power held within it than regular ron fuel - its just better able to withstand pre-ignition on a high compression (or forced induction) engine. the only gains from mpg I can forsee would be if the car wasn't set up to cope with 95 ron fuel (highly unlikly in this day and age) and was pinking all over the place when you were driving on it.

More power, yes (marginally - even on very highly tuned stuff like evos its only around 3-5% difference). More economy - no. I suspect other factors are in play

What's the point in paying more for something that you set on fire?

the only gains from mpg I can forsee would be if the car wasn't set up to cope with 95 ron fuel (highly unlikly in this day and age) and was pinking all over the place when you were driving on it

Oddly, modern engines are designed to knock with low octane fuel and use a knock sensor to back off the ignition at higher rpm to avoid it. It gives them better mid range performance and they benefit from high octane fuel.

yeah that's what I was alluding to - I've not known anything thats set up to run 98ron and doesn't have a knock sensor in the last few years. There's probably a couple of oddball cars out there, but even then it'd only really be a big issue at low rpm high throttle openings, once you're higher in the rev range the issue deminishes

V power every time for me (barring imminent run out of petrol). It definately goes further on a full tank of that. Think I've used normal unleaded a dozen times tops in this car when in desperation. It just seems to disappear far quicker!!

Right, so how does retarding ignition timing prevent knock? Is knock the same as pre-ignition? If so, surely it's something that happens without the spark, which is the problem..?

I've not known anything thats set up to run 98ron and doesn't have a knock sensor in the last few years

Even bog standard cars?

I get approx. 365 miles on full tank of 98 Ron and approx. 330 miles on full tank of 95 Ron.

(I used 95 Ron for about 6 months and now I've been using 98 Ron for roughly 10 months.)

Haven't bothered working out the cost difference.

I have tried BP Ultimate in the Prius and I didn't notice a big increase in MPG. Problem is it doesn't commute so does a load of different types of journey on any one tank so there are many other factors.

5lab - Member
there's no reason why higher ron fuel should give you more mpg. it doesn't have any more power held within it than regular ron fuel - its just better able to withstand pre-ignition on a high compression (or forced induction) engine. the only gains from mpg I can forsee would be if the car wasn't set up to cope with 95 ron fuel (highly unlikly in this day and age) and was pinking all over the place when you were driving on it.

More power, yes (marginally - even on very highly tuned stuff like evos its only around 3-5% difference). More economy - no. I suspect other factors are in play

If it's a forced induction engine, surely it can use higher boost with higher octane rate fuels? Thus it can attain higher torque and you can use lower gears, improving economy.

However using higher gears (as I think you meant) only applies when pootling about, on the motorway you'll be in top all the time anyway.

I think it's an ignition timing thing as above. Improves volumetric efficiency no?

Whoops, sorry. Yes, higher gears, not lower.

Retarded ignition timing is likely to reduce burn efficiency I guess?

P.s. I was reccomended to used v-power or similar in my TSI golf (similar engine to the OP), but I've not had it long enough to really test for any difference.

molgrips - bog standard cars are *very* unlikely to see any benefit from 98 ron car to start with. The benefits only come when you're in a highly tuned environment. I think fifth gear did a test which showed no improvement in a shopping car, something around 1% improvement in power in a clio 200 (or something else mildly hot) and around 3% improvement in power in a evo fq 360 (which short of the fq 400 has nigh on the most highly straigned production engine available today). Knock sensors have been standard on cars for over 15 years - because most cars are also sold in countries with very poor quality fuel, the knock sensors help the engine out

with regards to the 'keeping the car in a higher gear' - this could, I suppose, contribute, but how often do you change down when an extra 1% power would have meant you didn't change down? there will be a couple of circumstances, but not enough to make any meaningful difference to your mpg.

I've never understood why retarding the ignition prevents pinking/pre-ignition, but it does. I think its something to do with the speed of combustion, but its sadly beyond me.

ah - found the video from 5th gear - it was a clio, golf gti and a impreza. clio got no benefit, gti (warm turbo'd engine) got 2.5%, the impreza got 7%

...so why is my car lying to me and telling me I've covered 365 commuter miles with 98 ron against the 330 commuter miles i used to get with 95 ron?

cos your driving style has differed? because you've done different driving? because you're filling the neck of the fuel tank as well as the tank? because traffic is lighter? because the weather is better? because its warmer?

there's nothing, at all, in science that could make your car more efficient with 98ron fuel. you may as well wear a bracelet with a magnet in

bog standard cars are *very* unlikely to see any benefit from 98 ron car to start with.

That's what I thought originally but someone else said otherwise up there ^^^

cos your driving style has differed? because you've done different driving? because you're filling the neck of the fuel tank as well as the tank? because traffic is lighter? because the weather is better? because its warmer?

there's nothing, at all, in science that could make your car more efficient with 98ron fuel. you may as well wear a bracelet with a magnet in

I hear what you're saying and I'm sure you've got your petrochemical/combustion science correct.
However, as I said above, my commute has not changed in traffic density, distance or route. I don't use the car at the weekends, we use another one.

I drove for 6 months on 95 ron and now 10 months on 98 ron. The mileage I'm getting is different.

there's nothing, at all, in science that could make your car more efficient with 98ron fuel. you may as well wear a bracelet with a magnet in

Well that't not strictly true though is it. By retarding pre detonation it ensures that a higher proportion of the fuel injected is burned at the correct time within the 4 stroke cycle, thereby increasing the amount of useful energy extracted. It is also a fairly simple thing to test as all you would need is an engine on a test bed to eliminate all other variables.

gonefishin +1 - engine management systems are designed to cope with fairly poor grade fuels, if you can guarantee higher fuel quality then the engine management system can tweak the variables available to it in order to make the process more efficient.

The modern world.

The poster can afford a flash car but can't work out the fuel consumption... no wonder the UK is going to the dogs.

Yeah, it's political correctness gone mad, isn't it 🙄

My pub explanation.
"It's simple - Petrol is mainly a mixture of Heptane and Octane, with 7 and 8 carbon chains. The longer the chain the higher the chemical stored energy - more bonds to break requiring energy but considerably more energy released when these rebond with oxygen - exothermic. RON rating (research octane number) indicates the ratio of Heptane to Octane, higher the RON the higher the ratio of longer chain Octane in the fuel so more vvrooom. Mines a Mahito please."

I drove for 6 months on 95 ron and now 10 months on 98 ron. The mileage I'm getting is different

That's enough for seasonal factors to come into play. Petrol engines are more efficient when the air's warm because it's less dense and you need less fuel for stoichiometric ratio. You'll see less power at max throttle, but more economy at normal cruising speeds.

Gonefishin - sounds reasonable, I wonder if the 5th gear test was invalid because the cars didn't have any time to adapt their maps to the new fuel..? And IIRC that was quite a while ago wasn't it?

I drove for 6 months on 95 ron and now 10 months on 98 ron. The mileage I'm getting is different

Perhaps the engine is now run in.......

Switch back to 95 ron for a few months and see if mileage reverts to old figure.

I don't remember the 5th gear test but I do remember one on the Gadget Show that did show a difference, but to be honest I'm not sure that I'd trust either of those shows. All I've pointed out is a [i]possible[/i] mechanism as to why there may be improved performance/economy, it doesn't necessarily mean that there is one. Also, whether or not it is economic to use the more expensive fuel is another question entirely.

I seem to find that V-Power does provide better economy compared to standard fuel. I know the fuel light isn't the most scientific method but from full to light V-Power gives a consistent 30 miles extra, which I reckon easily offsets the extra cost of the fuel.

even BP only claim that you get an average improvement of 13 miles extra per tank, which they put down to lubricating components in the fuel, as well as cleaning elements. Assuming a 600 mile tank (bp are unlikely to have tested this on a small car), that's an improvement of 2% - so in mpg terms - assuming 35mpg, it'd be approx 0.6mpg improvement

http://www.bp.com/sectiongenericarticle.do?categoryId=9018273&contentId=7033278

I expect if some cars magically did an extra 5mpg, bp, shell et al would probably be advertising the fact

How many petrol cars do 600 miles on a tank?

More likely 400 miles which makes it a massive 3% improvement.. 🙂

Still on the Prius that could mean an extra 2mpg if you are lucky.

Do people really get improved performance on 98 ron? IMO its more placebo in terms of acceleration. However it definately makes engines smoother and tends to get more mpg if driven sensibly.

Do people really get improved performance on 98 ron? IMO its more placebo in terms of acceleration.

Doesn't apply to older cars and even relatively new motorcycles though.

Perhaps the engine is now run in.......

Switch back to 95 ron for a few months and see if mileage reverts to old figure.

Well, the car had 55K on the clock when I got it and now it has 72K. I reckon that's run in enough.