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:
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 ;-)

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

Expense.

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.

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.

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.

"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.

"Christian McArdle" wrote in message
.. .
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.


I wouldn't have thought there would be a significant difference in energy
content. High octane fuel is less susceptible to premature detonation but a
consequence of this is a slightly slower burning fuel. The reason it sounds
"better2 could be a result of that. It's likely that you'll get slightly
worse mpg for a engine tuned for 95RON.

If the ignition timing can be altered to take advantage of the fuel, you'll
get more power and fuel economy than before.

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 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.

So increasing the octane rating does not reduce the energy content?

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

"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

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.

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.

So increasing the octane rating does not reduce the energy content?

No, increasing the octane rating does reduce the energy content. This then
can be compensated for by reformulating the fuel to increase the energy
content to mask the effect.

Christian.

In article ,
Mike Barnes wrote:
I often fill up with 97 RON fuel (not 99, I've never seen that) and
although I don't monitor fuel consumption carefully, it's my impression
that it does give more miles per gallon than the usual 95. I'm also
pretty sure that the effect isn't great enough to make up for the
increased cost (often a bigger difference than the 4p you quote).

My engine was designed for 97 RON although it will run happily on 95.
The manufacturer's (Audi's) consumption figures refer to 97, which leads
me to believe that it's better than the figure for 95, but it might be
that they have to select same the fuel for performance and economy
figures, and choose best performance.

I travel to the North of Scotland quite often and usually do one way on 95
octane, and the other using Super 97-99 or whatever. I use the cruise
control where possible set at the same speed. And I can't honestly say
I've found a verifiable difference in either performance or economy. My
car is sort of the same as yours saying 95 octane on the filler but
suggesting in the handbook higher octane may be better. So I'd guess
*most* EU cars are optimised for 95 octane.

My old Rover, however, with no ECU control over ignition, objects loudly
to 95 but runs well on 97. Of course it originally ran on 4 Star leaded.

--
*Why don't sheep shrink when it rains?

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

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.

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.

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.

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

So would fixing the timing :-)

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 ...

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.

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.

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.

"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..

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.

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?

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?

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"?

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.

In article
Chris Bacon wrote:
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"?

That's like saying of a circle "diameter or radius?"

"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.

In article ,
Chris Bacon wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.

No they don't.

Of course they do. It's the volume of the cylinder and combustion chamber
with the piston at BDC related to the volume with it at TDC.

--
*I don't have a license to kill, but I do have a learner's permit.

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

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 |
\================================================= ================/

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

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

No they don't.

Of course they do. It's the volume of the cylinder and combustion chamber
with the piston at BDC related to the volume with it at TDC.

Rolls eyes - the "stroke of the piston" does not equal
the volume. Your first statement is nothing like your 2nd.

In article ,
Chris Bacon wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.

No they don't.

Of course they do. It's the volume of the cylinder and combustion
chamber with the piston at BDC related to the volume with it at TDC.

Rolls eyes - the "stroke of the piston" does not equal
the volume. Your first statement is nothing like your 2nd.

The quoted stroke of the *engine* is a different matter since that's a
linear measurement. The 'stroke' of the piston is fine to describe its
movement from BDC to TDC.

--
*Middle age is when it takes longer to rest than to get tired.

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