Sainsbury's Super Unleaded

[Jonathan Kay]

Could you do the experiment blinded as to what fuel is in? Get someone else to fill it and not tell you...

 

Jonathan

[AMMO]

If you are not running high enough compression to warrant super unleaded I wouldn't bother. My 260 bhp 2 litre Duratec was built with 11:1 compression ratio and runs fine on Tesco 95 octane fuel. No misfires or nothing weird. I used to put Optimax or BP 97 octane in for trackdays but the last couple of times I couldn't be bothered and just ran the 95 octane with no problems.

 

The big power engines I have built with 12:1+ CR run 97 octane super unleaded. In the old days of racing air cooled V twins with 12.7:1 CR we did testing with the then available 98 octane BP Supergreen (the best performance pump fuel at the time) against 100 octane Agip world Superbike control fuel and 109 octane ELF. Didn't see any difference on the dyno, so stuck to the cheaper 98 octane pump fuel. The ELF fuel cost a fortune, gave me a headache and made me vomit when I breathed the fumes of some that had been spilt. The exhaust fumes from the bike would make your eyes water.

 

A few years ago at a dyno shootout at Emerald, Peter Carmichael turned up with his K-Series and did back to back testing of 95 octane against 97 octane fuel. The engine made more power on the 95 octane. The conclusion was that the 95 octane fuel has higher calorific value.

 

My rule of thumb for quite a few years has been anything up to 11.2:1 I suggest customers use 95 octane. For compression ratios higher than 11.2 then go to the higher octane fuel.

 

We had one case where some 12:1 engines I built were run by the customer with 95 octane fuel. Nothing bad happened. Which makes me think that 95 octane fuel will run at higher compression ratios than my safe rule of thumb 11.2:1.

 

 

[Looptheory]

Quoting AMMO: 

If you are not running high enough compression to warrant super unleaded I wouldn't bother. My 260 bhp 2 litre Duratec was built with 11:1 compression ratio and runs fine on Tesco 95 octane fuel. No misfires or nothing weird. I used to put Optimax or BP 97 octane in for trackdays but the last couple of times I couldn't be bothered and just ran the 95 octane with no problems.

 

The big power engines I have built with 12:1+ CR run 97 octane super unleaded. In the old days of racing air cooled V twins with 12.7:1 CR we did testing with the then available 98 octane BP Supergreen (the best performance pump fuel at the time) against 100 octane Agip world Superbike control fuel and 109 octane ELF. Didn't see any difference on the dyno, so stuck to the cheaper 98 octane pump fuel. The ELF fuel cost a fortune, gave me a headache and made me vomit when I breathed the fumes of some that had been spilt. The exhaust fumes from the bike would make your eyes water.

 

A few years ago at a dyno shootout at Emerald, Peter Carmichael turned up with his K-Series and did back to back testing of 95 octane against 97 octane fuel. The engine made more power on the 95 octane. The conclusion was that the 95 octane fuel has higher calorific value.

 

My rule of thumb for quite a few years has been anything up to 11.2:1 I suggest customers use 95 octane. For compression ratios higher than 11.2 then go to the higher octane fuel.

 

We had one case where some 12:1 engines I built were run by the customer with 95 octane fuel. Nothing bad happened. Which makes me think that 95 octane fuel will run at higher compression ratios than my safe rule of thumb 11.2:1.

 

 

That seems pretty conclusive then i reckon , thank you AMMO

[Ozzy]

I thought the bigger problem at the moment, was the amount of Ethanol in cheaper fuels, and the detrimental effect it has on older cars with rubber seals/hoses, which is why a lot of people are using the expensive stuff. Or is that another myth?

 

Oz.

[Jonathan Kay]

*arrowup* *arrowup*I don't think that's a myth. FBHVC have notes on discussions with the Department for Transport

 

Jonathan

[Garry7]

My Duartec Roadsport has been on the road since June this year and has run pretty much exclusively on Tesco 95 ron for its 1700 miles to date. Only problem so far has been running out of it on the motorway!!

It has had a couple of tankfuls of Shell 95 but has run the same throughout.

I accept that it is probably too soon to find out about the ethanol effect but thought I'd post it up anyway.

[Dr Slotter]

Quoting AMMO: 

A few years ago at a dyno shootout at Emerald, Peter Carmichael turned up with his K-Series and did back to back testing of 95 octane against 97 octane fuel. The engine made more power on the 95 octane. The conclusion was that the 95 octane fuel has higher calorific value.

To add to this, the 95 octane fuel will probably have had a higher calorific value but that is independent of its octane rating. Apologies for some repetition of points already made by other people, but it'll make more sense if I do that!

 

Broadly speaking, you'l get more power out of an engine running a higher compression ratio because more useful energy is extracted from the fuel as it is more efficient thermodynamically. The down side of higher compression ratios is the tendency for fuel to explode randomly (pre-ignition/knock) rather than burn nicely. To get around this you need to use higher octane fuel.

 

One of the ways to make higher octane fuel is to add ethanol, which has a lower energy density (calorific value) than gasoline, thus lowering the energy density per volume. When used in an engine that needs it, although lower energy density fuel is being used, the total power output is greater because the thermodynamic cycle is more efficient than the fuel contains less energy (if you see what I mean!) e.g.

 

Lower compression ratio engine of 45% efficency using a fuel with 100 'energies' = 45 'useful energies'

Higher compression ratio engine of 55% efficency using a fuel with 90 'energies' = 49.5 'useful energies'

 

(made up numbers)

 

If you use the higher octane rated fuel in a lower compression ratio engine that does need need the anti-knock properties you just end up with less energy out.

[Jonathan Kay]

Please could you explain about lower octane fuel having higher calorific value? Is this a well-known fact, and what's the underlying chemistry?

 

Thanks

 

Jonathan

[Dr Slotter]

Probably best explained by more arbitary numbers!

 

Gasoline = 100 'energies' per volume

Ethanol = 80 'energies' per volume

 

95 octane fuel = 100% gasoline

98 octane fuel = 90% gasoline, 10% ethanol

 

95 octane fuel = 100 'energies' per volume

98 octane fuel = (90% x 100) + (10% x 80) = 98 'energies' per volume

[Jonathan Kay]

Thanks

 

Does all current UK fuel that has RON >95 use ethanol to achieve that?

 

Jonathan

[Dr Slotter]

And to put this back into my previous example:

 

(1) Lower compression ratio engine of 45% efficency using a the 95 octane fuel with 100 'energies' = 45 'useful energies'

 

(2) Higher compression ratio engine of 55% efficency using a the 95 octane fuel with 100 'energies' = 55 'useful energies' in theory but the resulting pre-ignition would drop the thermal efficency massively.

 

(3) Lower compression ratio engine of 45% efficency using a the 98 octane fuel with 98 'energies' = 44.1 'useful energies' i.e. hardly any difference to (1).

 

(4) Higher compression ratio engine of 55% efficency using a fuel with 98 octane fuel with 98 'energies' = 53.1 'useful energies' i.e. more power even though the 'energies' per volume is less.

 

This is all massively simplified and doesn't take into account, for example, ECUs changing the ignition timing to account for the fuel type being used.

 

 

[Dr Slotter]

Quoting Jonathan Kay: 

Thanks

 

Does all current UK fuel that has RON >95 use ethanol to achieve that?

 

Jonathan

 

I'm not sure to be honest, it all depends on the requirements of the formulation. I think ethanol (or indeed methonal) is popular with standard retail pump fuel because it can be bio-derived and helps with emmissions (less NOx etc. and a lower carbon to hydrogen ratio for CO2). There are quite a few different types of octane boosters such as iso-octane, toluene and some others I can't remember, there was one that was banned because it had a lot of lead in it for example. Tolulene used to be used a lot in racing fuels to produce fuel suitable for very high compression ratio engines where outright power is most important, but not sure about it at the moment.

[Jonathan Kay]

Thanks

 

Jonathan

[AMMO]

One thing I forgot to mention was that at the time I was looking into fuels I was told that the octane rating of fresh fuel at the pump is often higher than advertised. This is so that the octane rating can be a guaranteed minimum.

 

In other words if the fuel is left in the tank for a long period of time even after it has deteriorated it is still the correct octane rating. I was told that the BP Supergreen 98 octane fuel available in the 90's actually exceeded 100 octane. This would explain why when compared to Agip 100 octane WSBK control fuel on the dyno there was no difference in engine performance. It might also explain why the 12:1 engines designed and mapped to run on 98 octane still ran fine with 95 octane. My theory is that the 95 octane fuel when fresh is actually higher than advertised. It would be good if someone working in the industry could actually confirm this as I have no proof. Just based on what I was told many years ago.

 

I have left half a tank of fuel in the Caterham when it was off the road and the engine has always started up fine with no misfires and perfect running on fuel that was several months old. In fact I can think of only once when fuel has caused misfires and that was when it was found to have water in it. Otherwise misfires are always something else, usually electrical.

 

Fuel is something I never worry about in my engines. You buy either 95 or 97 octane according to the compression ratio. Most customers who have spent a lot of money on a performance engine will always go for Shell or BP. For engines with lower compressions supermarket 95 octane seems fine. I can vouch for my local Tesco. There are always big queues there so I assume the fuel is always fresh. All in all, the stuff you buy at the pump, although rather expensive, seems to do its job.

[Dr Slotter]

Yep, octane ratings on pumps are in theory a 'guaranteed minimum' for the fuel they deliver. Fuel does obviously deteriorate over time, the extent of which depends on how it is kept and the resulting change in perceived performance obviously depends what you run it in. Pump fuel has a higher octane on delivery to the forecourt to ensure that it meets the minimum rating on pump delivery.

 

AMMO's example of pretty standard fuel kept in a 'sealed' dark container (car fuel tank) and then run in a relatively low compression engine (I assuming that his Caterham is such from his comments) is one where the deterioration of the fuel and performance reduction would both be minimal. An opposite example would be when I used to race karts with very high compression ratio two stroke engines we used the highest octane fuel we could use, blended with the appropriate volume of fancy two-stroke oil, octane boosters etc. That mixture would last about three weeks before it made an engine run like a very poorly thing.

 

My attitude to pump fuel, based on what I've seen with my own cars and knowing a bit about how it all works, is the following:

 

- all bog-standard 95 octane fuel is pretty much the same, supermarket or branded station. As AMMO says, you could argue going to a busy forecourt gets you fresher fuel rather than a small village station that gets a delivery every month. The fuel is likely to come from any of the UK's refineries, although clearly geographical convenience means a particular forecourt will get fuel from the same source most of the time. My Caterham (a 175bhp Duratec) mostly receives 95 octane fuel from either Tesco or BP purely down to which direction I'm going when leaving home.

 

- 'premium' fuel is a bit different in that different producers choose to vary the formulation and additive package to differentiate their product in the marketplace. Depending on how they have produced the higher octane rating (see my previous post), the life of fuel can be different. Different additives cause fuel to deteriorate at a different rate but not so much that you'd notice. If the hardware/software on a vehicle needs and can detect/make use of higher octane fuel you can usually see a few MPG increase as it can run more efficently. AFAIK in the UK the premium fuel for a particular branded is made in one place, vPower at Ellesmere Port for example, so there could be a benefit there for consistency but also the fuel has to travel further to be delivered! Both my Clio 182 and Focus ST had engine that could do that and I did see small improvement of MPG, particularly in the Clio. I'm more sceptical about the benefit of fuels that coat your engine in 'stuff' and 'clean' it. It is true that the majority of losses in an ICE are due to friction, but most of the contacts where that can be reduced are not any where near where the fuel ever goes.

 

 

 

Edited by - Dr Slotter on 1 Sep 2012 11:00:16

[MonkeyBoy]

Not much to add, other than confirm that it's the same base fuel but it's the better quality additive package that costs more. Other benefits are that some additives will better lubricate the fuel pump and some types of fuel injectors, some additives prevent the fuel 'going off' for longer, and more expensive fuels have 'better' detergent additives. Not saying that it's worth paying more for or not.

 

Cheers

 

[Z3MCJez]

Thanks Ammo and Dr Slotter. Interesting food for thought.

 

I have tested (in my tintop) 1000 miles of 95 Shell vs 97 Shell and recorded about 2mpg better with the 97. This more than negated the additional cost, and although I haven't done a test on statistical significance, I believe that the driving conditions were not such that 2mpg was a different mix of driving.

 

I also use 97 in the Caterham, in an engine which is clearly designed for 95 (Sigma 140). However, it does everything, when warm, at foot to the floor (It's a track-only car) and I'm prepared to "invest" in the additives. Again, I use Shell whenever I can. I've heard the calorific value point from a friend in the industry, but he believes that the difference is unlikely to be noticeable, even at the margins, if the fuel is branded. He won't use supermarket fuel, full stop, and he drives a 2002 Honda barge.

 

Jez

 

ETA The tin top was designed for 97

 

Edited by - Z3MCJez on 3 Sep 2012 23:58:51

[john milner]

I've read posts on many forums that say things such as premium rated fuel "only" giving 2-3mpg extra. That works out at about 10% or 13-14p a litre which if true is quite a big difference. I can't see how the octane rating can be doing anything so if there is any benefit it must be from the additives.

 

One thing I have learnt is that oft-mentioned knock sensor functionality is usually described incorrectly. Having one doesn't allow higher octane fuel to be used but allows an engine to run on lower rated fuel without any problems. e.g. if the engine is optimised for 100 then 95 is OK albeit not ideal.

 

Not sure what I got out of my last fill (standard Shell). It was probably similar to standard supermarket but too difficult to judge as I had to re-fill early. Currently running on standard BP.

I'm likely to get through a couple of tankfuls of Sainsbury's Super over the weekend so might learn something useful.

[Dr Slotter]

Quoting 11884: 

I've read posts on many forums that say things such as premium rated fuel "only" giving 2-3mpg extra. That works out at about 10% or 13-14p a litre which if true is quite a big difference. I can't see how the octane rating can be doing anything so if there is any benefit it must be from the additives.

 

One thing I have learnt is that oft-mentioned knock sensor functionality is usually described incorrectly. Having one doesn't allow higher octane fuel to be used but allows an engine to run on lower rated fuel without any problems. e.g. if the engine is optimised for 100 then 95 is OK albeit not ideal.

 

Octane rating by itself does not giver extra power, just allows more efficient combustion in certain designs of engines. In my 2) example earlier, data from a knock sensor would cause the ECU of the engine to change the timing for prevent pre-ignition effectively making it the same as example 1).

[john milner]

Octane rating by itself does not giver extra power, just allows more efficient combustion in certain designs of engines. In my 2) example earlier, data from a knock sensor would cause the ECU of the engine to change the timing for prevent pre-ignition effectively making it the same as example 1).

 

I doubt that a standard ECU would be able to derive any extra power from higher octane fuel. From my very limited experience and other anecdotal evidence there might be something in the additives that aids economy although I'm far from convinced yet.

Sainsbury's Super is probably the best price for a premium rated fuel and has quite a few favourable comments from those who need higher RON. Tesco's Finest(or whatever it is called) has the worst comments.