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We own a 1.6 grand Cmax . The last time we drove to Cornwall it was down to third gear on some of the long A road drags.
I vowed that next time we would hire a nice powerful car. Having seem the price of car hire I got to thinking if premium petrol would improve its performance on the big hills?
Would it make any difference ?
Ummmm......... not really, no!
Absolutely none. Can make a small percentage difference in cars with turbos and decent power already.
Could you get it remapped ?
My i20 needed first gear for some of the hills last summer.
It's not very well...
I doubt it would make much difference, other than better economy. I get 10% better fuel on a run with E5 Super than E10. If the car is fully loaded, you'll need to keep the rev's in the power band for petrols.
Both our cars have the same power output, but mine is a 1.8 and MrsF's is 1.6. Same Manufacturer. My car is a bit heavier, but it's also quicker and has more torque due to the engine being a little bigger. Mine is also much better in the hills of North Wales and doesn't require the gear changes. The only time I've needed the gears is with four blokes and four trail bikes on the roof !
I understood that unless you went for the higher octane stuff then basically they were just normal fuel with a bit of detergent in to keep your engine internals a bit cleaner. Possibly noticeable over 50,000 miles but not to Cornwall and back. Even if you stuck with Shell Premium for 50,000 you probably have paid enough extra to have the whole engine replaced anyway, so as above, not really worth it.
When I had a puma years back I sometimes put posh petrol in. It made a small improvement in fuel economy but not enough to cover the extra cost. No noticeable change in performance when driving. It’s basically snake oil isn’t it?
🤣 having similar concerns with my old 1.6 zafira that will be loaded with camping gear, bikes, and people when we go down there this summer. Its flat as a fart at the best of times, but any hills or load on board and you've just got to be patient and not even consider overtaking anything 🤣
What about putting some in diesel for extra torque on the hills?(!)
Having seem the price of car hire I got to thinking if premium petrol would improve its performance on the big hills?
No. High performance cars are sometimes tuned to take advantage of it and will have to fall back to safer settings when using normal petrol. If you have such a car, it will reach its full performance on higher octane petrol, but it'll make no difference in a normal car.
It’s basically snake oil isn’t it?
Well no, insofar as it's a real thing, it is higher octane and it does have cleaners in it. The marketing is way off the mark though and is very misleading.
flip side is i disagree on a long run youll recover the cost of premium fuel easily. However it wont give you +100hp that you require.
Posh petrol will make no difference to power output of a normally aspirated (non-turbo) petrol engine :o(
It's Cornwall not the Alps - there's a few drags but you just go slow on those bits!
And there will be a stream of campers and caravans going slower than you! 🙂
Slightly different story with diesel though - fancier diesel does run a little bit better in all diesels, but not a lot. It does clean up your engine slightly, it'll start better and run somewhat smoother, but in a newer car they are so smooth anyway it doesn't make that much difference.
My own experience was a few more mpg which meant the same cost per mile. No noticeable performance benefit.
Could you get it remapped ?
No point on an NA petrol.
Now an engine swap with an ST170, hmmmm.
I put a couple of tanks of posh diesel through my (diesel 🙂 ) van annually. I hope that the injectors appreciate the gesture, no power difference noted
See thats where a bigger engine car would be more economical on motorways etc.
I always used to have small engined cars, then got a 2.0 diesel. Wouldnt go for a small output (power) engine again as they use more fuel and less comfortable to drive... apart form around town.
In performance engines I try to avoid supermarket fuel, usually filling up at a local relatively competitive shell but with 95 octane. I run a tank of Shell V-Power through every 3-5000 miles as I believe the additional additives help clean the injection system. For track days, I always use whatever Super Unleaded is available as it does protect the engine under continuous abuse (especially motorbikes) and the modest performance gain becomes noticeable.
If you have a vehicle you're going to leave unused for many months, it's not a great idea to leave E10 in the system as it absorbs water faster and the additional solvents can damage the injection system.
In a vehicle with a regular engine, I just run what's cheapest. I think it's probably more important to not run to near empty, so you don't bring up whatever containments in the tank that are floating at the top.
No difference in power. Did however give me 49.7 MPG on a 500 mile motorway haul, up on 44.3 MPG on the (slower) outward trip using E10. effectively an additional 75 miles before the light went on.
In a vehicle with a regular engine, I just run what’s cheapest. I think it’s probably more important to not run to near empty, so you don’t bring up whatever containments in the tank that are floating at the top.
I usually use BP/Shell etc. But in the last few months its been about 20p per ltr more than a local independent garage. Using their fuel economy dropped immediately from roughly 49mpg to about 42 mpg. I imagine if I used super dooper fuel it would go up in to mid 50's
Every so often I use posh stuff as it does clean the engine a little.
Just a thought - How old is the C-Max?
I drive a 15yr old Type R and it runs a lot better on premium fuel (E5) than the new E10 unleaded.
Just a thought – How old is the C-Max?
2012
Just take a run-up!
Don’t know about posh petrol, but my old 1.8 cmax (2004 vintage so could be different to yours) did not like supermarket petrol at all. I never bothered with the fancy stuff, but had to swap to shell/BP or similar otherwise it bogged down horribly and was awful pulling away if you were in a hurry
I'd be looking at whether anything is hindering the car. Incorrect fuel mixture, vacuum leaks, etc. Most modern cars will tell you this.
Then I'd give it a good service, air filters, plugs etc.
In reality you probably want a more powerful car.
See thats where a bigger engine car would be more economical on motorways etc.
Not convinced by that. Of course diesels are more efficient, but a larger NA petrol engine is not likely to be more efficient than a smaller one on motorways, provided it has high enough gears. Small displacement, lower revs and a wider throttle is probably the most efficient way to burn petrol without a turbo, I'd guess.
twas obvious i'd pop in....
I get 10% better fuel on a run with E5 Super than E10.
These figures are always difficult to quantify, as the effect is not always down to what you think the cause is.
Ethanol has ~30% less energy density to it, so the extra 5% is only 2.5% less energy density in an E10 over an E5 -we measure these things as LHV (Lower Heating value) - so to get 10% improvment is not possible notwithstanding other factors..
other factors..
Liquid density - 2 x fuels with a comparable liquid density say 0.735, one E5 one E10 you will see a slight drop -10% is still a high figure. However, take the E10 with a higher density, say 0.75 (this may seem small but it's not) and your volumetric energy density is actually greater than that of the E5 - and this is what the car can make use of.
Additive packs - there a re 2 types - Keep clean and Get clean, with the later being reerved for premium fuels i.e. vpower types. These will arguably have a greater impact on the perfromance of the vehicle, oftern restoring it to t's original optimised performance (clean valves and injectors), and in some cases prioviding a benefit through flame modification additives (i.e. you can modufy flame speed in combustion making it more efficient).
Octane - not the bee all and end all of fuel quality, far from it actually its nothing more than a knock indicator. Most cars will have traditional maps for 95-97RON, some will have one for 100RON, but certainly nothing over that. They will also have protection maps for ~93RON in the UK. The ECU's will leean, or use Lambda sensors to adjust timing -efficiency gains are had when the combustion can start as close to "top dead centre" of the stroke - higher quality fuels allow this to happen -especialy knock resitance - if you try to achieve TDC with a low octane fuel you can get knock/detonation and destroy piston heads and or valves. However Octane doesn;t exist in fuels as singluar number, it's made up from 200+ chemicals that all contrbute, and those chemicals atomise and burn and different speeds -so a 98RON Octane in one fuel may not be as good at avoiding knock of 98RN in another fuel.
there's todays chemistry and engineering lesson.
Just take a run-up!
Used to do that in my old 1000cc Mini (proper one!) - you'd rag the arse of it on the downs. Speedo needle hitting the limiter pin then rapidly go down the gears when the uppy bit started! 🤣
back to the point anyway.
under constant high loads you should always use a fuel with good cleaning performance. High load applicaitons cause depositis very quickly, which will either sit on valves (ecpecially in PFI engines), or on injectors becuase they stay very hot posh fuel will assit with this. On the point of a hot engine, Ethanol has a positive impact from its charge cooling effect so can help with heat managment. - Anyway, just use a decent branded fuel - just avoid the very cheap supermarlet ones as they skimp on the add packs.
edited for a freuding slip
Posh petrol will not solve the issue of a steep hill and a heavily loaded and modestly powered car.
back to the point anyway.
under constant high loads you should always use a fuel with good cleaning performance.
Great info, thanks @Sui.
So when I'm towing a 2.5 ton load 120 miles should I ideally be using 'premium' fuel [3.0L diesel] - I try to get my fuel from Costco as it's not only cheaper but, they say, it's good quality* also.
* May not not actually be true
Just a well known brand (Shell, BP, Total, Esso) will do the job @sharkbait - im not sure what Costco's supply/spec is like (didnt even know they did it tbh)
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<div class="bbp-reply-content">Posh petrol will not solve the issue of a steep hill and a heavily loaded and modestly powered car.
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it will certainly protect the car over an above non-posh fuel (i.e. supermarket)
I don't get a noticeable performance increase in my 2l NA petrol. But the fuel economy increase is more than equal to the extra cost. A good extra 50 miles from a 40L tank
Even if you stuck with Shell Premium for 50,000 you probably have paid enough extra to have the whole engine replaced anyway, so as above, not really worth it.
Because I like playing with numbers, using some average numbers
Normal fuel = £1.70 per litre
Premium fuel = £1.90 per litre
Assumed MPG = 50
Over 50,000 miles, the premium fuel would cost £909 extra, assuming no change to fuel economy. A 5% improvement in fuel economy would reduce the difference to £497
I notice a performance and fuel economy difference. I tend to only use “posh fuel”. I do have a performance engine though. I also use Redex every 1000 miles or so.
I tend to do a fair bit of motorway driving, I don’t speed but can get up to the speed limit reasonably quickly.
Whether or not it’s worth it is a different question. I’m happy to think that my engine is getting the cleanest fuel it can have.
Normal fuel = £1.70 per litre
Premium fuel = £1.90 per litre
With peoples estimates in previous posts of about 10% extra fuel economy, at best the posh petrol nearly pays for itself.
So WHY BOTHER?
My car does run appreciably smoother and uses a little less fuel with Super Unleaded, particularly Tesco 99ron momentum. But it is a turbo and the manual advises 98ron. It will run on 95 and I don’t worry if I have to use it, so much of the time I guess it is running on about 97ron. Whether the smoothness is due to the higher Ron or the reduced ethanol I wouldn’t like to say.
Just a well known brand (Shell, BP, Total, Esso) will do the job @sharkbait – im not sure what Costco’s supply/spec is like (didnt even know they did it tbh)
Unless you live in Scotland in which case your petrol came through the INEOS refinery at Grangemuoth no matter what the petrol station is branded...
As for the rest if the UK only EXXON in the above list has a refinery in the UK. Do you relly think that those other companies ship their fuel from their refineries abroad or do you think they just buy it wholesale?
If you are just looking for a bit more pep uphill I suggest a Car Nitrous Kits from Wizards of NOS. That'll do it. Big red button to push anytime you need a boost. Bolt on and at least another 50bhp under you bonnet.
Coincidentally I read this yesterday
Unless you live in Scotland in which case your petrol came through the INEOS refinery at Grangemuoth no matter what the petrol station is branded…
As for the rest if the UK only EXXON in the above list has a refinery in the UK. Do you relly think that those other companies ship their fuel from their refineries abroad or do you think they just buy it wholesale?
The UK is a net importer of fuel, and Fawley (Exxon) is not the only operational refinery in the UK at all -there are 6 - and yes everyone ships everything everywhere - its a very complex model operating at very thin margins, so shipping of a boat and then bringing in a boat really does happen. Base quality of fuel does change all over the UK, as such the add pack treatment rates also change depending on where the base material comes from (to an extent).
To this using redex type things on top of premium fuels -you really shouldn't, you're overdosing and can form "gumming" as a consequence.
Unless you live in Scotland in which case your petrol came through the INEOS refinery at Grangemuoth no matter what the petrol station is branded…
It doesn't matter if it all comes from the same refinery. Different customers have different additive packs added, at the refinery I think.
I predict this thread will be longer than the delay the OP has being a bit slower up a couple of hills 😀
Using Shell V Power in my 97 Nissan Primera there was a noticeable difference in torque which allowed me to shift up earlier/stay in a higher gear. A much improved driving experience, mpg improved by about 10% which covered the extra cost and I never used anything else. When I bought a 2010 Toyota Verso, couldn't feel any difference so stopped using it after filling up twice. I'm not sure about the difference between supermarket premium and others. I would try it, at least you would know.
AHH good, Sui has chipped in. Nothing more to add, other than when short on fuel I had to use Morrisons yesterday... I'll be topping up with v-power when I get a chance. At least I found somewhere with 97 Ron.
So WHY BOTHER?
I'd be less concerned about using it in a petrol engine unless its a high performance car.
On a diesel, it's of much more importance. Modern diesel engines have a massive task in keeping emissions and pollution in check. Things like EGRs and DPFs in diesel engines are very temperamental. Modern diesel engines are at a high risk of carbon build up internally which causes a lot of problems.
One way to mitigate that is using the best fuel possible. As has been mentioned in other posts, the premium fuel and the non-supermarket fuels have more additives added to them and those additives help reduce some of the longer term issues that modern diesel engines have to deal with.
Speaking of hire cars, I was also looking the other day for a trip in May and yeah the prices are pretty crazy at the moment, much more expensive than I remember.
Presumably we've all seen those horror Yoo Toob vids of filthy direct injection intake manifolds after sub 50k miles? They always seem to need walnut blasting at very low mileages which seems odd. Is this the sort of thing soopa fuels deal with or are you still going to get reaaallly dorty and need cleaning anyway. Diesel and/or petrol engines BTW
Modern diesel engines are at a high risk of carbon build up internally which causes a lot of problems.
I would say that a modern petrol engine, if it's direct injection as most are, is at much worse risk. Removing the cylinder head to clean out all the gunk is a regular service job on many!
Is this the sort of thing soopa fuels deal with or are you still going to get reaaallly dorty and need cleaning anyway. Diesel and/or petrol engines BTW
In a normal petrol engine, the fuel is injected into the inlet so some petrol cleans out the valves. But in a direct injection engine it goes into the cylinder, so only air and recirculated exhaust gasses go into the intake. Consequently, they get gunked up. So fancy fuel makes no difference there.
This can happen to diesels too but as long as you don't abuse your engine it doesn't need cleaning out every 50k miles, I'm not sure why.
Can the fuels be mixed? Or do you have to run your car (near enough) completely empty?
Similarly for if you then went back to non super do you have to drain the tank empty?
This is asking from a diesel 2.0td perspective but any info would still be useful! Have always wondered this.
you can mix them. Many folk will fill up with premium every other fill or so.
Personally I use premium in both my cars (a diesel Mazda and a petrol Abarth 595)
Normal but branded (non supermarket) fuel user here, but I've got a 2.0 euro6 Ford diesel engine with a wet belt so have bigger things to worry about than dirtying up the engine internals.
No car I've owned ever had a sufficient increase in MPG using premium (higher RON) fuel over regular fuel to cover the increased cost per litre, including everything from big normally aspirated, small capacity turbo'd and high-revving VTEC engines. YMMV, literally.
As for the ruddy hills along the A30 in Cornwall, probably the only time I've wished I could travel legally at car speeds. Our van won't maintain speed up the hills there if you hit the bottom of them at the van speed limit.
I never really understand (literally don't understnad the chemistry) all the hate for supermarket fuel. I pretty much always fill up at Tesco ( for the points = tunnel crossings). My last couple of cars have been v high mileage without issue. 200k on a diesel passt and 160k+ on a diesel SMax. I'm not saying branded isn;t better but is it realy that much better for the extra cost?
Also, If I fill up my 2.2l Merc Viano with super cool diesel or what ever its called, how much extra mpg will I get on a trip down to the Alps?
Thanks @ Sui: Every time I read about E10 causing huge drops in fuel economy (Daily Mail clickbait headlines) I get a bit of a nervous tic.
OP a 1.6 Grand C Max (ecoboost) will cheerfully drink any kind of E5, E10 or a supposedly "performance" 95octane fuel.
TBH youre better off just making sure your car is properly serviced (new oil filter and clean, new oil makes a huge difference), the tyres are both in good nick and inflated properly (if the car is to be fully loaded take the pressures up to the full load recommendation) and FFS dont sit on on a motorway at 80-90mph+....
Using anything other than normal pump fuel is pretty much pointless unless you strongly feel that the oil companies need some additional support during these hard times.
I always used to have small engined cars, then got a 2.0 diesel. Wouldnt go for a small output (power) engine again as they use more fuel and less comfortable to drive… apart form around town.
Very much the other way around.
Most engines / vehicle combinations are more efficient somewhere close to flat out. That's not the same as saying a 3.5l V8 is more efficient at 150 than a 1.6 i4 at 110, but the i4 will be more efficient than the V8 at 110.
i.e. a 1.0 NA petrol engine that barely did 70mph would be the most efficient (petrol) option if it existed.
A 2.0 Diesel works well in the same car because it's doing 2000rpm rather than 4000rpm so the actual volume of air/fuel is about the same (whilst the turbo isn't running).
It's more noticeable motorbikes because there's a greater range of engines to chose from in similarly sized vehicles. A 250cc bike will do 80mpg at motorway speeds all day long. A liter bike will do half the mpg because the throttle is barely cracked open.
The exception that proves the rule are the edge cases like when Top Gear raced an M3 Vs a Prius round their track and got 17mpg in both. Because the prius spent the whole time trying to accelerate which is using the same amount of fuel as going flat out, but not going as fast.
Presumably we’ve all seen those horror Yoo Toob vids of filthy direct injection intake manifolds after sub 50k miles? They always seem to need walnut blasting at very low mileages which seems odd. Is this the sort of thing soopa fuels deal with or are you still going to get reaaallly dorty and need cleaning anyway. Diesel and/or petrol engines BTW
In principal anything that burns cleaner will recirculate less crap into the intake of a direct injection engine.
In reality:
a) stop doing short journeys you could walk is much better advice. And unlike other engine issues, an Italian tune up or occasional motorway run won't reverse the process.
b) if it's a problem, then fancy fuels once a month won't help in the slightest. 'cleaning' action is mostly just of the injectors, you can get some additives that will persist a bit longer and burn crap off the catalyst. But my gut feeling is any additive that persists after combustion is probably what's blocking the EGR, so more =/ better.
c) By the time there's solid gunk in there the only way it's coming out is by scrubbing/blasting it.
The UK is a net importer of fuel, and Fawley (Exxon) is not the only operational refinery in the UK at all -there are 6
I didn't say that only exxon has a refinery in the UK I said that of your list ie. BP, Total, Shell and Exxon only Exxon has a refinery the the UK. the remaining refineries being owned by others, having been sold by the like so BP, Total & Shell!
It doesn’t matter if it all comes from the same refinery. Different customers have different additive packs added, at the refinery I think.
Additives yes but not to the point or 95 and 97 RON. There is no difference between "branded" and "Non Branded" petrol so buy whatever from where ever you want. Whilst there is a difference between 95 & 97 RON everything else is snake oil, don't kid yourself otherwise.
My old mechanic used to advise me to use the fancy stuff every third or fourth tank. This is in Germany where supermarket fuels don't exist.
2.5l T5
I seen to remember that it felt like there was more grunt /acceleration was keener.
Since having the Ducato (from new) I've only filled it with the "cheap" stuff. Seeing as I'm now in Spain and fuel seems much cheaper here than Northern Europe. My covered 11,000km since new.
Posh petrol will not solve the issue of a steep hill and a heavily loaded and modestly powered car.
Absolutely this. When I had a 1.7 Zetec Puma, I’d put in a tankful of Shell VMax, just to clean everything out, and I’d make sure I used the best possible oil, just because the engine didn’t have iron bore liners, the bores were Nickasil plasma coated, and vulnerable to wear.
Over the course of two years I was in and out of Cornwall three or four times a week on average, driving a wide range of vehicles including C-Max, B-Max, in fact pretty much every model of Ford, but they were all unladen and only me in them, and I can’t say I noticed any real performance issues, in fact the only car I can remember that really struggled was a Fiat 500X, the bloated SUV/crossover, which was a real slug! On uphill sections of the A30/303, M5 and M4 I was down into 3rd with my foot flat on the floor and barely getting 60mph out of the horrid thing.
An NA engine, as has been pointed out, will struggle with a full load, and nothing can change that. The little 1.0 EcoBoost motors are a world apart, mine delivers 125bhp, and about the same amount of torque, but the same engine in some bigger cars has a map that gives 140bhp, and corresponding levels of torque, it’s the turbo and map that’s important.
I nearly always use Sainsbury’s fuel, it’s been consistently cheaper locally, but I’ll use whatever’s available and cheapest, and I’ve never noticed and difference in performance; that’s using E5. Getting an oil change just before Christmas seemed to make a difference though, very much for the better.
ran my old integra type R pretty much only on v power but that was only as it was mapped for 98 from the factory.
havent got a clue if it improved mpg but could tell the differance performance wise.
never used it in anything else, not even my track car, power to weight in that was so good just got it mapped on standard fuel as didn't think the small gains where worth it.
Posh petrol is for higher compression engines. Typically turbos but some NA call for higher octane too.
You can run lower octane fuel and get less mpg, it won't break anything.
Running higher octane in an engine designed for low octane fuel is wasting money.
Looks like the 2012 came in a 1.6 and a 1.6 EcoBoost. Like most early gen direct injection engines, don't the EcoBoosts suffer from valve sludge? Could be time for a clean-out.
Turbo engines don’t always have higher compression ratios. In fact the block may have a lower ratio to deal with the already compressed air without putting undue stress on the engine. BMW M54 (NA) has the same compression ratio as the N55 (FI) and the B58 (FI) is only higher due to larger bores.
Higher octane fuel is more effective in larger engines only because as a percentage gain, it’s more significant on higher power engines.
Running a tank every so often is a bit daft as the ECU won’t fully adapt to the new fuel over a single tank, then will run suboptimal on the next tank.
My M3 and Z4M and even my e46 wagon all run better on 99 than 95. Smoother and less revs for the same speed. I also don’t seem to get the problems others with e46s do with gummed TBs etc. I’ve only ever used v-power or occasionall Tesco momentum 12 years ago when there wasn’t a Shell station within 20miles.
I use posh petrol in my old motorbike as it has less ethanol in it.
My M3 and Z4M and even my e46 wagon all run better on 99 than 95. Smoother and less revs for the same speed
it changed your gear ratios ??
It depends on the car.
on a cmax (unless its turbod) then probably nothing.
i do notice that the golf (1.4tsi (turbo)) rx8 (high compression ****le ) M3 (NA v8) RS4 (na V8) Q2 (turbo'd) Q5 (2.0 tsi) have all provided better mileage on premium fuel. they have also ran smoother. I do not use supermarket fuels on my cars as i find they dont run as well. If they dont cause an issue for you go for it and enjoy the cheaper petrol.
it changed your gear ratios ??
I was meaning throttle, but you knew that.
Not helping the OP at all, but as a diesel owner who is paranoid about not driving a Honda anymore and scared of DPFs/modern engines and emissions, I use an additive in my diesel which works out cheaper than Super Diesel
https://www.hydra-int.com/kerosene-cebo-cetane-booster-lubricants.html
Cetane boost.
Cant say it makes much difference to mpg, and cant notice any driving difference, or its very minimal. But thats what I want. I dont want blockages etc, so I dont want to notice anything if you get me.
I tend to use Tesco. Tesco stations are controlled by exxon if remember rightly and their fuels are very similar (but not the same).
With my 1.5tsi Skoda, I average 40mpg with E10 petrol, if I use momentum 99 E5, thats goes up to 45mpg, which is a 12.5% increase.
Filled yesterday, E10 was 139.9 and momentum 99 was 146.6, which is a 4.7% difference in price.
Therefore its a no brainer for me to run the more expensive fuel as it works out cheaper per mile. The other advantages of running posh fuel is just a bonus.
I was meaning throttle, but you knew that.
So it was getting more power from the same amount of air, that's possibly even more impressive than a magic gearbox unless it was a turbo'd version.
Octane ratings only prevents pre ignition at high compression. High compression only occurs at wide open throttle because at part throttle you have a manifold vacuum which translates to the compressed charge in the engine being nowhere near the ~10x atmospheric pressure the compresion ratio implies.
scared of DPFs/modern engines and emissions
You probably don't need to be. I took the EGR pipe off my Passat for a good clean after about 150k miles, there was just a light film of soot inside it at one end. As long as you're doing some miles you're fine. Even the cooler was just a bit dirty, not remotely blocked.
So it was getting more power from the same amount of air, that’s possibly even more impressive than a magic gearbox unless it was a turbo’d version.
Absolutely possible, in fact, the whole point of higher RON fuel - if you can advance the ignition more before knock then you will get more power for a given AFR. This is literally the reason for calibrations being able to react to higher RON fuel. Doesn't have to be turbo-charged, it is all down to the ignition mapping and whether the EMS can detect and correct for higher/lower RON fuel.
This isn't the 80s - Better fuel, better combustion, your ECU will adjust the stoichiometric ratio and advance the timing to match what's happening in the engine/exhaust. Less fuel required for a given speed/power demand.
Octane ratings only prevents pre ignition at high compression. High compression only occurs at wide open throttle because at part throttle you have a manifold vacuum which translates to the compressed charge in the engine being nowhere near the ~10x atmospheric pressure the compresion ratio implies.
This is incorrect; knock (pre-ignition is different to knock) can happen at any engine load if the ignition is advanced too far, or if there are hot-spots in the cylinder, etc. Yes, it is more likely at higher loads and if the engine has a higher compression ratio or is at high boost (giving a functionally higher CR) but can happen anywhere.
Obviously if the calibrator has done their job properly then knock at low-loads isn't going to happen, but there will still be advantages in mid-load regions with a higher octane fuel to advance the ignition.
Most modern engines - even smaller, non-performance ones - will be mapped at 99RON to form the base ignition maps and then will have corrections applied based on the knock levels seen by the EMS. Running < 99RON will see some knock increases and the EMS will learn a global offset required to ensure knock seen is below a given threshold across the entire engine map or, for some EMS, the offset is applied separately in a grid across the engine map (so more knock susceptible areas will have a higher retard offset than those that don't see much knock).
On an engine mapped as above (which is any I have done - engine calibrator by profession for 15 years) there is an absolute difference in how the ECU runs on different octane fuels. HOWEVER, whether that gives any appreciable difference in end result is down to the engine. A small, non-performance engine it will be negligble, more powerful ones it will become noticeable. Ignition advance is proportional to engine torque for a given engine speed and load (air mass) by way of an efficiency curve. Advance moves you up the efficiency curve, retarding down it. The curve is flatter at the most advanced end and steeper at the most retarded end. So the advance you get from increased octane moves you from high efficiency to higher effiency and might be 1-3% on the efficiency curve, depending on the speed/load you are running. Obviously that then translates to if your engine is making more torque than another then 1-3% is going to be more or less noticeable.
Good informative answer, thanks.
Should we also expect slightly better MPG with higher octane then if the timing can be advanced?
Interesting reading, all of the above posts.
If I put expensive electricity in my battery will I get better performance over using cheap electricity?* 🤔
* I only own battery powered torches, but the extra run time/lumen output might be beneficial when I head out in the dark.
If I put expensive electricity in my battery will I get better performance over using cheap electricity?* 🤔
no but you could use a more expensive more energy dense battery for better performance.
Should we also expect slightly better MPG with higher octane then if the timing can be advanced?
Yeah, there will be some improvement as you are making better use of the air/fuel charge.
As it happens, I popped into Sainsbury’s this afternoon to top up the tank, and put in E10 by mistake, just not paying attention, so it’s half- and- half. I can’t imagine it’s going to make any significant difference really, though.
@speed12, whereabouts are you, and what’s the going rate for a remap of an EcoBoost 1.0, currently at 125bhp?
This is incorrect; knock (pre-ignition is different to knock) can happen at any engine load if the ignition is advanced too far, or if there are hot-spots in the cylinder, etc. Yes, it is more likely at higher loads and if the engine has a higher compression ratio or is at high boost (giving a functionally higher CR) but can happen anywhere.
When my car was last on a rolling road, the chap on the laptop said it needed most work mid load to prevent knock. 3 litre turbo 8v Inline 4 and 9.something to 1 compression ratio. Which is quite high for an old fashioned turbocharged engine. It has to run on posh petrol due to the fuel lines and the high CR.