Supermarket Petrol

[Grumpy Cabbie]

If they used turbo-charged 1.0VVTi's it'd probably work better (Plus the weight saving would provide a large mpg boost; I really don't get why the HSDs have such large engines - The Yaris HSD's petrol engine is the biggest engine in the range!)

Is it something to do with the Atkinson cycle causing a significant lack of torque in acceleration, which is topped up by the electric side of the hybrid? That's why when I try and drive up a steep hill with 2/8 bars of Battery the car is slower and much harsher than if I attempt it with a full Battery where it pretty much flys up. There's a balance between making the car driveable with a low Battery and fuel econony?

I guess an idea situation is an Atkinson 1.0 engine which is fine when you have full or even half battery and would be very economical (remember the original Insight), but you'd lose interest in such a car when you tried to go up a steep hill with a full car but with a depleted battery (you could have been stuck in a traffic jam at the bottom for example).

Perhaps a simplistic explanation is that an Atkinson engine without a hybrid system would be like the old non turbo diesel engines from the early 1980's. Great on the flat, fabulous fuel economy, but shocking on a hill or under acceleration.

[Joseph D]

From a technical perspective an engine tuned for RON 95 will not benefit from RON 98. And as modern low compression petrol engines are the target market for RON 95, then that is what you should use in them. The Prius' Atkinson cycle-like engine even more so because in effect it is a super (or should that be hyper) low compression engine.

The average punter assumes that the higher the RON (Research Octane Number) the more power (or grunt or umph) the petrol has, but this is not the case. This misunderstanding is not helped by distributors calling RON 95 standard or regular and RON 98 super, premium, ultimate or momentum (the sole purpose of which is to extract more £££'s out of the unsuspecting).

In fact the RON is an indicative "antiknock index".

"The fuel property the octane ratings measure is the ability of the unburnt end gases to spontaneously ignite under the specified test conditions. Within the chemical structure of the fuel is the ability to withstand pre-flame conditions without decomposing into species that will autoignite before the flame-front arrives. Different reaction mechanisms, occurring at various stages of the pre-flame compression stroke, are responsible for the undesirable, easily-autoignitable, end gases."

(Adding ethanol, incidentally inhibits the spontaneous ignition characteristic as well.) This spontaneous ignition, known as pinking or knocking, is very bad for your engine and over a short time can damage internal components such as bearings and journals. Running on is also symptom of the wrong petrol. These problems typically occur when RON 95 petrol is used in a high compression engine tuned for RON 98. Modern engine management computers may use "knock" sensors and delay* the timing of the ignition to protect the engine from damage. You will not usually notice much, by the way of these types of symptoms, when you use RON 98 in a low compression engine tuned for RON 95.

[Edited to be more accurate, due to new information. The quote in italics above is directly from here section 6.3 What fuel property does the Octane Rating measure?, as it explains octane ratings much better and technically more accurate than I did originally.]

[Edit: * the nanny censor will not let me use the more natural term r e t a r d. LOL. That is the problem when censorship takes place out of context. Grrrr]

Anyone use Tesco's 99Ron Momentum petrol? What you think of it?

not tried this yet.... Has anyone else got experience to offer on the economy difference between super unleaded and regular ?

I reckon you would need to get about 6% better fuel economy to make it worthwhile at todays prices ( about 7p more per litre)

Any way, the real point of this post was I had the same question and tried to research RON 95 petrol v's RON 98/99 petrol, and had the most fun time I have had in a while trying to sift through anecdotal "evidence", incomplete detail (people failing to state whether they use std or premium), people chipping with their diesel info, etc, etc. So out of sheer frustration, I decided to conduct my own research.

To keep things as consistent as possible, I decided to use a single brand.

I was already using Shell V-Power because in my earlier research I picked up various snippets of info that claimed the additives used by Shell were "better" at keeping your engine clean and ship-shape on the inside and wanted to "test" this out for myself. As I had already been using Shell V-Power and had a couple of tanks under my belt by the time I decided to "conduct" this new research, it was a logical base from which to launch. Shell V-Power Unleaded and Shell Fuelsave Unleaded were duly selected.

A large percentage of the driving on this test was travelling on A road single carriageway doing a mix of 55 - 66 mph indicated (75%). The remainder consisted of Motoways doing 68 - 75 mph indicated (15%) and 10% urban 30 - 44 mph indicated.

So after using 3 tanks of V-Power RON 98 (Feb - Jun) and 4 tanks of Fuelsave RON 95 (Jun - Jul), I have concluded that there is no benefit whatsoever in using RON 98, and in fact, 2 out of the 3 tanks (the first and the third) of V-Power produced worse economy even taking into account the seasonal change from winter into spring (meaning the third tank should have been better than the second). June and July have been fairly consistent temperature wise 12 - 18 deg C (mostly toward the 18 deg end), although through June there was quite a bit of rain. The rain might be part of the reason for the drop in MPG of the second Fuelsave tank (55.4 mpg).

As for the detergent component of the additives, Shell at least, uses the same detergents in Fuelsave as V-Power - at least from what I have read.

Here is my data:

Date  Fuel type -------------- Miles Litres MPG02/12 Shell Premium Unleaded   481.0 40.44  54.105/12 Shell V-Power Unleaded   187.0 14.87  57.206/12 Shell V-Power Unleaded   477.0 41.11  52.706/12 Shell Fuelsave Unleaded  458.0 34.37  60.606/12 Shell Fuelsave Unleaded  431.0 35.35  55.406/12 Shell Fuelsave Unleaded  549.0 42.14  59.207/12 Shell Fuelsave Unleaded  531.9 40.04  60.4

I hope this helps others in some way.

[CO2SLAVE]

From a technical perspective an engine tuned for RON 95 will not benefit from RON 98. And as modern low compression petrol engines are the target market for RON 95, then that is what you should use in them. The Prius' Atkinson cycle-like engine even more so because in effect it is a super (or should that be hyper) low compression engine.

The average punter assumes that the higher the RON the more power (or grunt or umph) the petrol has, but this is not the case. This misunderstanding is not helped by distributors calling RON 95 standard or regular and RON 98 super, premium, ultimate or momentum (the sole purpose of which is to extract more £££'s out of the unsuspecting).

In fact the RON is an indicative index of the amount of octane in the petrol. Octane is added solely to inhibit the explosive characteristic of petrol for use in high compression engines to prevent the petrol prematurely self detonating during the compression cycle. (Adding metanol, incidentally inhibits the explosive characteristic as well.) This premature detonation, known as pinking or knocking, is very bad for your engine and over a short time can damage internal components such as bearings and journals. Running on is also symptom of the wrong petrol. These problems typically occur when RON 95 petrol is used in a high compression engine tuned for RON 98. Modern engine management computers may use "knock" sensors and !Removed! the timing of the ignition to protect the engine from damage. You will not usually notice much, by the way of these types of symptoms, when you use RON 98 in a low compression engine tuned for RON 95.

Anyone use Tesco's 99Ron Momentum petrol? What you think of it?

not tried this yet.... Has anyone else got experience to offer on the economy difference between super unleaded and regular ?

I reckon you would need to get about 6% better fuel economy to make it worthwhile at todays prices ( about 7p more per litre)

Any way, the real point of this post was I had the same question and tried to research RON 95 petrol v's RON 98/99 petrol, and had the most fun time I have had in a while trying to sift through anecdotal "evidence", incomplete detail (people failing to state whether they use std or premium), people chipping with their diesel info, etc, etc. So out of sheer frustration, I decided to conduct my own research.

To keep things as consistent as possible, I decided to use a single brand.

I was already using Shell V-Power because in my earlier research I picked up various snippets of info that claimed the additives used by Shell were "better" at keeping your engine clean and ship-shape on the inside and wanted to "test" this out for myself. As I had already been using Shell V-Power and had a couple of tanks under my belt by the time I decided to "conduct" this new research, it was a logical base from which to launch. Shell V-Power Unleaded and Shell Fuelsave Unleaded were duly selected.

A large percentage of the driving on this test was travelling on A road single carriageway doing a mix of 55 - 66 mph indicated (75%). The remainder consisted of Motoways doing 68 - 75 mph indicated (15%) and 10% urban 30 - 44 mph indicated.

So after using 3 tanks of V-Power RON 98 (Feb - Jun) and 4 tanks of Fuelsave RON 95 (Jun - Jul), I have concluded that there is no benefit whatsoever in using RON 98, and in fact, 2 out of the 3 tanks (the first and the third) of V-Power produced worse economy even taking into account the seasonal change from winter into spring (meaning the third tank should have been better than the second). June and July have been fairly consistent temperature wise 12 - 18 deg C (mostly toward the 10 deg end), although through June there was quite a bit of rain. The rain might be part of the reason for the drop in MPG of the second Fuelsave tank (55.4 mpg).

As for the detergent component of the additives, Shell at least, uses the same detergents in Fuelsave as V-Power - at least from what I have read.

Here is my data:

Date   Fuel type -------------- Miles  Litres  MPG
02/12  Shell Premium Unleaded   481.0  40.44   54.1
05/12  Shell V-Power Unleaded   187.0  14.87   57.2
06/12  Shell V-Power Unleaded   477.0  41.11   52.7
06/12  Shell Fuelsave Unleaded  458.0  34.37   60.6
06/12  Shell Fuelsave Unleaded  431.0  35.35   55.4
06/12  Shell Fuelsave Unleaded  549.0  42.14   59.2
07/12  Shell Fuelsave Unleaded  531.9  40.04   60.4

I hope this helps others in some way.

Very helpful indeed , thankyou for your time and effort on this. I am convinced now that it makes no discernable difference so I will save myself some pennies and stick to Shell regular unleaded.

[Cyker]

If they used turbo-charged 1.0VVTi's it'd probably work better (Plus the weight saving would provide a large mpg boost; I really don't get why the HSDs have such large engines - The Yaris HSD's petrol engine is the biggest engine in the range!)

Is it something to do with the Atkinson cycle causing a significant lack of torque in acceleration, which is topped up by the electric side of the hybrid? That's why when I try and drive up a steep hill with 2/8 bars of Battery the car is slower and much harsher than if I attempt it with a full Battery where it pretty much flys up. There's a balance between making the car driveable with a low Battery and fuel econony?

I guess an idea situation is an Atkinson 1.0 engine which is fine when you have full or even half battery and would be very economical (remember the original Insight), but you'd lose interest in such a car when you tried to go up a steep hill with a full car but with a depleted battery (you could have been stuck in a traffic jam at the bottom for example).

Perhaps a simplistic explanation is that an Atkinson engine without a hybrid system would be like the old non turbo diesel engines from the early 1980's. Great on the flat, fabulous fuel economy, but shocking on a hill or under acceleration.

Ahh, that's a good point... Yeah, they would have needed a bigger Atkinson-cycle engine to deliver the same torque as a regular Otto-cycle engine. But then it makes me wonder - Why go Atkinson-cycle at all then? The Atkinson-cycle is more efficient but if you have to make it bigger to provide the required pull, you get a weight penalty plus you lower the mpg anyway (Bigger cylinders automatically cost you more fuel, esp. in petrol engines).

The 1.0VVTi would be much smaller and lighter, and on paper is only slightly less efficient in terms of raw peak mpg, but as Aygo owners know it can rev up to deliver a surprisingly good punch for its size.

The Atkinson is very efficient at the expense of torque which would make it great for a generator engine but not for anything that needs to deliver any sort of pull; The HSD would need to gear it down quite a lot (eCVT in action baby!) to keep the car moving under load, possibly to the point of it hitting the rev limiter

I think they did intend on the leccy motor to make up the shortfall but as you say that doesn't leave much contingency if the battery is exhausted...

Heh, maybe when hybrids become more popular, ricers will start modding them for power and we'll see 1.0 and 1.3VVTi's being retrofitted into them!

Or maybe the 1.5 Atkinson will get swapped with the 1.5 from the T-Sport!

[Opifex]

Looking back over my records, I have filled with 98 octane petrol three times and each time the mpg has been about 10% lower than the fill-ups before and after. Each time it was on the long motorway run from UK to Provence so the conditions before and after were about the same. My normal tipple is supermarket 95 octane and I've only used the posh stuff when it was that or use E10, but looking back the E10 seems to lower the mpg by less than the 98 octane so I'll be using the cheaper stuff in future.

A bit off-topic, I've often seen Shell V Power recommended for keeping the engine in good condition and thought I'd try it when my wife's old Polo had a mysterious stalling habit. Two fills with Shell V Power and the problem disappeared.

[Joseph D]

I had exactly the same question as the OP, so rather than start a new thread, I thought I would reply to this one.

Yes, I filled up for the first time with Sainsbury's unleaded (Morecambe, Lancashire, if that makes a difference), drawn by the super-cheap price (£1.279) and have noticed an immediate drop in MPG from my normal late 50's to early 60's to now struggling to get above the early 50's. <snip>

Just an update, I have just finished the Sainsbury's Unleaded tank and in the end I got 57 mpg which is not to be sneezed at. My last 3 tanks got 59.2, 61.6, 60.4 mpg, so this latest figure is not really outside the margin of error.

About half way through the tank I accidentally reset the mpg and milage readings on the Consumption screen (which I am not in the habit of doing) and because of this I noticed that the the mpg figure was more normal than when at the beginning of the tank. The final mpg displayed on the screen was something like 60.1.

That got me thinking, is the engine management computer smart enough to adjust for different grades of petrol? Probably not - as much as this would be a good thing. But I still wonder, what caused the bizarre readings at the start of the tank.

[kenphd]

i use bp it my be a few pence more but it will be a better fuel in the lon run

[Terry953]

i use bp it my be a few pence more but it will be a better fuel in the lon run

You pays your money and takes your choice, if you want to make an informed choice digest the information here :-- http://miniwww.tripod.com/gasoline.htm#9

[Joseph D]

You pays your money and takes your choice, if you want to make an informed choice digest the information here :-- http://miniwww.tripo.../gasoline.htm#9

Wow, Terry, what a document!

I have found it most interesting, although I can tell you that I have not read it in its entirety. That will take me several sessions to fully take it all in.

I note that in my earlier post, I was a little inaccurate in the detail of pre-ignition and octane, [now updated and hopefully more accurate], but the gist of my post still holds true - don't waste money on higher RON rated fuel than is required by your engine.

Also a couple of other take aways from the linked document:

• All fuels are not equal, even among "brand" names, as the additive package use by one company over another can and does make a difference. I would hazard a guess also that one brand of fuel is not "the best" for all vehicles.
  
• Formulations of fuels are altered for technical reasons seasonally to overcome problems related to temperature and altitude and this primarily is the reason for what we Prius/Hybrid owners can testify to from our observations in regards to Summer v's Winter economy figures.
  

Anyway, thanks again Terry for the link to this highly informative document.

[Cyker]

My last three tanks of V-Power Diesel were getting me ~66mpg, and my last tank which was Sainsburys diesel has clocked in at 74mpg!

[Wayne2015]

From a technical perspective an engine tuned for RON 95 will not benefit from RON 98. And as modern low compression petrol engines are the target market for RON 95, then that is what you should use in them. The Prius' Atkinson cycle-like engine even more so because in effect it is a super (or should that be hyper) low compression engine.

The average punter assumes that the higher the RON (Research Octane Number) the more power (or grunt or umph) the petrol has, but this is not the case. This misunderstanding is not helped by distributors calling RON 95 standard or regular and RON 98 super, premium, ultimate or momentum (the sole purpose of which is to extract more £££'s out of the unsuspecting).

In fact the RON is an indicative "antiknock index".

"The fuel property the octane ratings measure is the ability of the unburnt end gases to spontaneously ignite under the specified test conditions. Within the chemical structure of the fuel is the ability to withstand pre-flame conditions without decomposing into species that will autoignite before the flame-front arrives. Different reaction mechanisms, occurring at various stages of the pre-flame compression stroke, are responsible for the undesirable, easily-autoignitable, end gases."

(Adding ethanol, incidentally inhibits the spontaneous ignition characteristic as well.) This spontaneous ignition, known as pinking or knocking, is very bad for your engine and over a short time can damage internal components such as bearings and journals. Running on is also symptom of the wrong petrol. These problems typically occur when RON 95 petrol is used in a high compression engine tuned for RON 98. Modern engine management computers may use "knock" sensors and delay* the timing of the ignition to protect the engine from damage. You will not usually notice much, by the way of these types of symptoms, when you use RON 98 in a low compression engine tuned for RON 95.

[Edited to be more accurate, due to new information. The quote in italics above is directly from here section 6.3 What fuel property does the Octane Rating measure?, as it explains octane ratings much better and technically more accurate than I did originally.]

[Edit: * the nanny censor will not let me use the more natural term r e t a r d. LOL. That is the problem when censorship takes place out of context. Grrrr]

Anyone use Tesco's 99Ron Momentum petrol? What you think of it?

not tried this yet.... Has anyone else got experience to offer on the economy difference between super unleaded and regular ?

I reckon you would need to get about 6% better fuel economy to make it worthwhile at todays prices ( about 7p more per litre)

Any way, the real point of this post was I had the same question and tried to research RON 95 petrol v's RON 98/99 petrol, and had the most fun time I have had in a while trying to sift through anecdotal "evidence", incomplete detail (people failing to state whether they use std or premium), people chipping with their diesel info, etc, etc. So out of sheer frustration, I decided to conduct my own research.

To keep things as consistent as possible, I decided to use a single brand.

I was already using Shell V-Power because in my earlier research I picked up various snippets of info that claimed the additives used by Shell were "better" at keeping your engine clean and ship-shape on the inside and wanted to "test" this out for myself. As I had already been using Shell V-Power and had a couple of tanks under my belt by the time I decided to "conduct" this new research, it was a logical base from which to launch. Shell V-Power Unleaded and Shell Fuelsave Unleaded were duly selected.

A large percentage of the driving on this test was travelling on A road single carriageway doing a mix of 55 - 66 mph indicated (75%). The remainder consisted of Motoways doing 68 - 75 mph indicated (15%) and 10% urban 30 - 44 mph indicated.

So after using 3 tanks of V-Power RON 98 (Feb - Jun) and 4 tanks of Fuelsave RON 95 (Jun - Jul), I have concluded that there is no benefit whatsoever in using RON 98, and in fact, 2 out of the 3 tanks (the first and the third) of V-Power produced worse economy even taking into account the seasonal change from winter into spring (meaning the third tank should have been better than the second). June and July have been fairly consistent temperature wise 12 - 18 deg C (mostly toward the 18 deg end), although through June there was quite a bit of rain. The rain might be part of the reason for the drop in MPG of the second Fuelsave tank (55.4 mpg).

As for the detergent component of the additives, Shell at least, uses the same detergents in Fuelsave as V-Power - at least from what I have read.

Here is my data:

Date  Fuel type -------------- Miles Litres MPG02/12 Shell Premium Unleaded   481.0 40.44  54.105/12 Shell V-Power Unleaded   187.0 14.87  57.206/12 Shell V-Power Unleaded   477.0 41.11  52.706/12 Shell Fuelsave Unleaded  458.0 34.37  60.606/12 Shell Fuelsave Unleaded  431.0 35.35  55.406/12 Shell Fuelsave Unleaded  549.0 42.14  59.207/12 Shell Fuelsave Unleaded  531.9 40.04  60.4

I hope this helps others in some way.

Nice and detailed - great report!