Out of complete curiosity I filled my car with 99 octane petrol at Tesco the
other day.

See http://www.greenergy.com/products/99_octane.html

99.9p/litre versus 95.9p for 95 Octane. Basically I suppose the same price
when measured in "pence per octane"

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?


David

vortex2 wrote:
Is there any negative side to running higher octane
fuel in your engine?

Expense.

vortex2 wrote:
Out of complete curiosity I filled my car with 99 octane petrol at Tesco the
other day.

See http://www.greenergy.com/products/99_octane.html

99.9p/litre versus 95.9p for 95 Octane. Basically I suppose the same price
when measured in "pence per octane"

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?


David


Poverty ;-)

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

Don't be so sure. It may run smoother and could, with tuning, increase
power, but it does not guarantee better fuel economy. Increasing the octane
actually reduces the energy content of the fuel. It is likely that the
formula has been tweaked to restore this, or very slightly increase it over
standard fuel, but you shouldn't expect a large increase in economy.

Higher octane fuel is generally much worse for the environment, due to the
need for larger quantities of nasty aromatics, like benzene.

Christian.

Christian McArdle wrote:
Increasing the octane actually reduces the energy content of the fuel.

I thought it just made it less susceptible to detonation.

Increasing the octane actually reduces the energy content of the fuel.

I thought it just made it less susceptible to detonation.

That's obviously the main feature and why you would want higher octane fuel.
However, it has the side effect of reducing the energy content of the fuel.

Take LPG, for example. This has a much higher octane rating and so can be
used in petrol engines very successfully without detonation. However, it has
a much lower energy content, which is why it gets much lower mpg than 95RON.

There are methods to restore the energy content of the fuel whilst
maintaining a high octane, but it won't happen by default.

Christian.

Christian McArdle wrote:
Increasing the octane actually reduces the energy content of the fuel.
I thought it just made it less susceptible to detonation.

That's obviously the main feature and why you would want higher octane fuel.
However, it has the side effect of reducing the energy content of the fuel.

What then is the actual reduction in the "energy content" between
petrols with different octane ratings?

That's obviously the main feature and why you would want higher octane
fuel.
However, it has the side effect of reducing the energy content of the
fuel.

What then is the actual reduction in the "energy content" between
petrols with different octane ratings?

That would depend very much on the individual fuel. Obviously, higher octane
fuels from reputable manufacturers will have been formulated to restore the
loss of energy content, so I would be surprised if there is any on general
sale (LPG excepted) that has a lower energy content in practice.

Christian.

The message
from "vortex2" contains these words:

I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?

It costs more! Not all engines are capable of making the best of higher
octane fuel - in fact, very few are.

Try asking in uk.rec.cars.maintenance instead.

--
Skipweasel
Pay no attention to that man behind the curtain.

Guy King wrote:
The message
from "vortex2" contains these words:


I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?


It costs more! Not all engines are capable of making the best of higher
octane fuel - in fact, very few are.

Try asking in uk.rec.cars.maintenance instead.

Depends on the engine management software. My old Saab 9-3 LT gives 10%
improved consumption using "big name" brands like Esso or Shell compared
to the bottom of barrel stuff from Tesco, Asda and cut price
independents. So for paying 1-2% more there's a 5-fold return.
But on a car with a less tuned engine you probably wouldn't get much
difference.

john2

In article ,
john2 wrote:
Depends on the engine management software. My old Saab 9-3 LT gives 10%
improved consumption using "big name" brands like Esso or Shell compared
to the bottom of barrel stuff from Tesco, Asda and cut price
independents.

All the Tescos round here sell branded Esso.

--
*I'm not as think as you drunk I am.

Dave Plowman London SW
To e-mail, change noise into sound.

"john2" wrote in message
...

Depends on the engine management software. My old Saab 9-3 LT gives 10%
improved consumption using "big name" brands like Esso or Shell compared
to the bottom of barrel stuff from Tesco, Asda and cut price independents.
So for paying 1-2% more there's a 5-fold return.

That is unlikely.
There is virtually no difference between them and they frequently come from
the same tank.

dennis@home wrote:

That is unlikely.
There is virtually no difference between them and they frequently come from
the same tank.

I can't recall which mag did the work, but recently saw a quite detailed
analysis following a batch of tests of different fuels. They compared
supermarket petrol, against branded and also (IIRC) Shell optimax. They
used three test vehicles; a Nissan Micra, a VW Golf GTI, and a Subaru
Imprezza WRX. The test was well done using a dynomometer to assess power
and torque delivery, and the tanks were correctly cleaned and the EMUs
reset between tests.

The results were interesting - the main upshot however was that on the
Micra the different (and more expensive) petrols made very little if any
difference to either the performance or the drivability of the car. On
the Golf there was some improvement in performance on the optimax (about
8 - 10 bhp IIRC) and a slight improvement in driveability. However on
the Imprezza there was a quite substantial improvement in power (over 25
bhp) and driveability.

So what you say about there being no difference seems to stack up - but
only on some types of car.

(Personally I find there is a discernable difference on my Subaru
between 99 and 95 RON, and it runs like a dog on any supermarket
offering I have tried)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
dennis@home wrote:

That is unlikely.
There is virtually no difference between them and they frequently come
from the same tank.

I can't recall which mag did the work, but recently saw a quite detailed
analysis following a batch of tests of different fuels. They compared
supermarket petrol, against branded and also (IIRC) Shell optimax. They
used three test vehicles; a Nissan Micra, a VW Golf GTI, and a Subaru
Imprezza WRX. The test was well done using a dynomometer to assess power
and torque delivery, and the tanks were correctly cleaned and the EMUs
reset between tests.

The results were interesting - the main upshot however was that on the
Micra the different (and more expensive) petrols made very little if any
difference to either the performance or the drivability of the car. On
the Golf there was some improvement in performance on the optimax (about
8 - 10 bhp IIRC) and a slight improvement in driveability. However on
the Imprezza there was a quite substantial improvement in power (over 25
bhp) and driveability.

So what you say about there being no difference seems to stack up - but
only on some types of car.


Th key issue is what the engine is optimised for.

If optimised for high octane, lower octane fuel will not burn optimally
- sure the anti-knock will stop any damage, but the combustion will then
be too late for optimal power. Putting higher octane fuel in will net
more power and more MPG.

If optimised for lower octane, the higher octane will burn too slow, and
again, the ignition timing may be automatically advanced to partially
compenatee, but at the end of the day, its not likely that the engine
will develp better power or efficiency, since it needs the higher comp
ratio to do that as ell as the better fuel.


(Personally I find there is a discernable difference on my Subaru
between 99 and 95 RON, and it runs like a dog on any supermarket
offering I have tried)



Ah, in the glorious days of carburettors and five star petrol, my MGs
ran best on 5 star, and a damp cool misty day, and weer rough old dogs
on 4 star on a dry hot day.

BTW as the formula one crowd discovered some years back when they were
unrestricted on fuel, apart from it being '95 octane' or something,
there are any amount of aromatic hydrocarbons you can add that will net
you huge power increases in high comp engines, acting as flame
retarders, and huge extra MPG, by being super dense..the fuel may have
passed the test for '95 octane' but pump fuel it was not. Highly
corrosive, highly carcinogenic and very very nasty stuff..

John Rumm wrote:
dennis@home wrote:

That is unlikely.
There is virtually no difference between them and they frequently come
from the same tank.


I can't recall which mag did the work, but recently saw a quite detailed
analysis following a batch of tests of different fuels. They compared
supermarket petrol, against branded and also (IIRC) Shell optimax. They
used three test vehicles; a Nissan Micra, a VW Golf GTI, and a Subaru
Imprezza WRX. The test was well done using a dynomometer to assess power
and torque delivery, and the tanks were correctly cleaned and the EMUs
reset between tests.

The results were interesting - the main upshot however was that on the
Micra the different (and more expensive) petrols made very little if any
difference to either the performance or the drivability of the car. On
the Golf there was some improvement in performance on the optimax (about
8 - 10 bhp IIRC) and a slight improvement in driveability. However on
the Imprezza there was a quite substantial improvement in power (over 25
bhp) and driveability.


The survey was on Fifth Gear, Channel 5 a couple of months ago. I
probably have a recording somewhere.

john2

dennis@home wrote:
"john2" wrote in message
...


Depends on the engine management software. My old Saab 9-3 LT gives 10%
improved consumption using "big name" brands like Esso or Shell compared
to the bottom of barrel stuff from Tesco, Asda and cut price independents.
So for paying 1-2% more there's a 5-fold return.


That is unlikely.
There is virtually no difference between them and they frequently come from
the same tank.

I have had good results from supermarket petrol but other times it feels
like I just piled a few heavy bags of sand in the boot when I filled up.
Also big name petrol at a price that sounds too good to true is usually
a disaster. I really think there's something going one here, not all
big name 95 petrol is the same and garages selling it really cheap must
be mixing it with something else or selling something different to the
label.

If your local supermarket petrol is reliably good, then fair enough, but
round here they certainly aren't.

john2

"Guy King" wrote in message
...
The message
from "vortex2" contains these
words:

I'm nearly convinced. Is there any negative side to running higher
octane
fuel in your engine?

It costs more! Not all engines are capable of making the best of higher
octane fuel - in fact, very few are.

Try asking in uk.rec.cars.maintenance instead.

My Dad got more MPG from 99 Octane in his old Sierra.

"vortex2" wrote in message
...
Out of complete curiosity I filled my car with 99 octane petrol at Tesco
the other day.

See http://www.greenergy.com/products/99_octane.html

99.9p/litre versus 95.9p for 95 Octane. Basically I suppose the same
price when measured in "pence per octane"

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?


David


For those who have pointed out the blindingly obvious - yes I know it does
cost more!

I should point out the manual for my car says:

"The engine can be driven witht he octane ratings 91, 95 and 98 RON."
"98 RON is recommended for maximum effect (sic) and minimal fuel
consumption."

If I see 4% less fuel usage then I have a neutral cost for using
superunleaded.

David

On Fri, 5 May 2006 11:18:53 +0100, "vortex2"
wrote:

I'm nearly convinced. Is there any negative side to running higher octane
fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.
A look in the data section of the handbook should clarify it.

In article ,
EricP wrote:
I'm nearly convinced. Is there any negative side to running higher
octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

That is simply wrong. High octane pertol burns *more slowly* than low. You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?

--
*Don't squat with your spurs on *

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 05 May 2006 15:36:59 +0100, "Dave Plowman (News)"
wrote:

In article ,
EricP wrote:
I'm nearly convinced. Is there any negative side to running higher
octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

That is simply wrong. High octane pertol burns *more slowly* than low. You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?

Sigh.

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

In article
EricP wrote:
snip

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

Combustion chamber, compression ratio, it's the crank that has a stroke
not the piston ...

Rob Morley wrote:
EricP wrote:
Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

Combustion chamber, compression ratio, it's the crank that has a stroke
not the piston ...

Hm. "stroke", or "throw"?

In article ,
EricP wrote:
That is simply wrong. High octane pertol burns *more slowly* than low. You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?

Sigh.

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

Not in any of the many many technical publications on IC engines I've read
over the many many years. ;-)

The stroke of the piston and the size of the combustion chamber determine
the compression ratio. If you have too high a compression ratio for the
octane of fuel used you'll have to compromise the performance and economy
by retarding the ignition. This is to *prevent* the mixture exploding and
causing pinking. If the octane rating is higher than required, absolutely
nothing untoward occurs.

Basically you've got things the wrong way round. Too low an octane rating
can damage an engine. Not the other way round.

--
*Whatever kind of look you were going for, you missed.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
The stroke of the piston and the size of the combustion chamber determine
the compression ratio.

No they don't.


Basically you've got things the wrong way round. Too low an octane rating
can damage an engine. Not the other way round.

AOL.

EricP wrote:
"Dave Plowman (News)" wrote:
In article EricP wrote:
I'm nearly convinced. Is there any negative side to running higher
octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel.

That is simply wrong. High octane pertol burns *more slowly* than low. You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?


Sigh.

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

"The stroke of the pistons"... do you mean the swept volume, or what?
Where does volumetric efficiency come into this, do you think?

"Chris Bacon" wrote in message
...
EricP wrote:
"Dave Plowman (News)" wrote:
In article EricP wrote:
I'm nearly convinced. Is there any negative side to running higher
octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel.

That is simply wrong. High octane pertol burns *more slowly* than low.
You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?


Sigh.

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

Correct.

"The stroke of the pistons"... do you mean the swept volume, or what?

Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and others).

Where does volumetric efficiency come into this, do you think?

It's got nothing to do with the compression ratio. (I may stand corrected).


Volumetric efficiency is related to the amount of air that is able to enter
the combustion chamber during the induction stroke
(4 stroke engine). It's helped by using better cylinder head design and
construction (which includes better induction manifold design and
construction). It's also helped by valve timing "overlap", and probably by
improved exhaust system design.
_Amongst other things_.

I used to own a BSA Blue Star 350cc OHV _single_ cylinder 1934 motorcycle.
This bike had _twin_ exhaust ports and exhaust systems. The only reason for
this, in my opinion, must have been an improved volumetric efficiency ( the
single inlet and single exhaust cylinder head valves were the same size).

Sylvain.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember EricP
saying something like:

I'm nearly convinced. Is there any negative side to running higher
octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

That is simply wrong. High octane pertol burns *more slowly* than low. You
won't damage any petrol engine by using a road fuel with a higher octane
rating than it actually requires. The only harm is to your wallet.

A look in the data section of the handbook should clarify it.

Perhaps you'd give a direct quote from one?

Sigh.

Dave it is all to do with the stroke of the pistons and size of
compression chamber. Believe me, it's factual!

Factual ********, you mean.
--

Dave

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

Quite the opposite. Higher octane fuels are able to take higher compression
ratios without exploding.

Basically, a diesel engine works by compressing the mixture enough so that
it could explode without a spark (it doesn't stick the fuel in until the
compression's done for that reason). Diesel engines use high compression
ratios (i.e. 20:1) to ensure that the fuel will definitely spontaneously
burn when injected. They also prefer low octane fuel that will burn without
encouragement, although with sufficient compression and a suitably designed
fuel system, they will burn any old filth, including high octane petrols.

A petrol engine doesn't want the fuel will go off early. It wants the burn
to start when the spark fires. To do this, you either have to reduce the
compression ratio (8:1 or thereabouts) or use higher octane fuel that
doesn't explode under pressure.

If you use a high octane fuel in a low compression engine, you're just
wasting money, as neither the high octane nor the cheaper fuel would have
exploded anyway, so you get no benefit whatsoever from the increased octane
rating.

The octane rating of a fuel gives little indication of its energy content,
except that most higher octane substances have lower energy content. This is
especially true when oxygen containing compounds are introduced, as the
oxygen can't be burnt, so is "wasted" mass. However, such compounds have
truly excellent octane rating. Ethanol, for example, is 130 octane, but only
contains something like 60% of the energy.

Christian.

Christian McArdle wrote:
The octane rating of a fuel gives little indication of its energy content,
except that most higher octane substances have lower energy content.

Heptane has an octane rating of 0 IIRC, so where does that
leave the above peculiar statement?

The octane rating of a fuel gives little indication of its energy
content,
except that most higher octane substances have lower energy content.

Heptane has an octane rating of 0 IIRC, so where does that
leave the above peculiar statement?

Well, for a start, n-heptane with a RON of 0 has more energy content than
iso-octane with a RON100, so it fits into the general pattern. However,
there are genuine counter-examples out there, although most just have a
lower octane than you would expect for the energy. Finding a high octane,
high energy fuel is more difficult!

The common octane improvers, such as benzene and toluene, which have octanes
in excess of 100, have lower energy content. Toluene, for example, has
40.5MJ/kg, compared to 44.4MJ/kg for iso-octane.

When you start adding oxygen (i.e. alcohols, rather than pure hydrocarbons),
you get much lower energy content for a massive increase in octane.

Christian.

The message
from EricP contains these words:

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

Er - no. Higher octane is more resistant to detonation, allowing higher
compression ratios, more advanced ignition timing and hotter engines.

--
Skipweasel
Pay no attention to that man behind the curtain.

EricP wrote:
"vortex2" wrote:
Is there any negative side to running higher octane fuel in your engine?

Yes, you could be wrecking your engine if the compression ratio can't
take the faster burning fuel. In simple terms, it goes bang faster
than lower octane ratings, so the engine must be flexible enough to
take it.

That's the wrong way around, there's enough misinformation around
already. You could say "it goes bang more predictably", I suppose.
Your first sentence would be sort of more correct for lower octane
fuels.

vortex2 wrote:
Out of complete curiosity I filled my car with 99 octane petrol at Tesco the
other day.

See http://www.greenergy.com/products/99_octane.html

99.9p/litre versus 95.9p for 95 Octane. Basically I suppose the same price
when measured in "pence per octane"

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).



One of the car shows on TV did a test and one car it made no difference
at all, another it increased the max hp marginally and another it
helped in the low-mid range but not in the high end. So it seems it's
good for some cars and not for others. Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

In article .com
wrote:
snip
Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

So would fixing the timing :-)

In article ,
Rob Morley wrote:
Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

So would fixing the timing :-)

You'd certainly expect the knock sensors to do their job.

IIRC, the M series is among the few where super is recommended.

--
*Don't worry; it only seems kinky the first time.*

Dave Plowman London SW
To e-mail, change noise into sound.

Rob Morley wrote:
In article .com
wrote:
snip
Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

So would fixing the timing :-)

It would, but BMW say it's normal and won't do anything.

In article .com,
wrote:
Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

So would fixing the timing :-)

It would, but BMW say it's normal and won't do anything.

I thought the M Series engines were meant to run on Super?

--
*There are two sides to every divorce: Yours and **** head's*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article .com,
wrote:
Tescos 99 stops my M3 from
making horrible low rpm pinking noises.

So would fixing the timing :-)

It would, but BMW say it's normal and won't do anything.

I thought the M Series engines were meant to run on Super?



The handbook says one will get more power and mpg from super but the
minimum RON is 95. Until recently all I could get around here was 97
and it still pinked. 99 from tescos works well but it still backfires
when cold. All "perfectly normal".

"vortex2" wrote in message
...
Out of complete curiosity I filled my car with 99 octane petrol at Tesco
the
other day.

See http://www.greenergy.com/products/99_octane.html

99.9p/litre versus 95.9p for 95 Octane. Basically I suppose the same
price
when measured in "pence per octane"

My car (5 year old Volvo) has never run better.

I've yet to see if there's an economy benefit (I'm sure there will be).

If yours is a turbo then yes you will find a marked improvment in
drivability and go. Volvo turbo's are renown for needing 98octane or more to
give their best.

MPG should be better by a couple of mpg too, as long as your driving style
is the same.

Tim..