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..

In article ,
The Natural Philosopher wrote:
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.

No standard MG was ever designed for 5 Star. Early Rover V-8s were, though.

Rough running on a hot day was usually down to fuel evaporation and SU
pumps. Later cars had a constantly circulating fuel rail to help keep it
cool

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..

--
*When cheese gets its picture taken, what does it say? *

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

Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
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.

No standard MG was ever designed for 5 Star. Early Rover V-8s were, though.

I don' care what they were designed for, I know what they ran best on ****.


Rough running on a hot day was usually down to fuel evaporation and SU
pumps. Later cars had a constantly circulating fuel rail to help keep it
cool

You really aren't listening are you.

The Natural Philosopher wrote:

No standard MG was ever designed for 5 Star. Early Rover V-8s were,
though.


I don' care what they were designed for, I know what they ran best on ****.

Does that make it a pussy wagon then?


--
Cheers,

John.

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

In message , John
Rumm writes
The Natural Philosopher wrote:

No standard MG was ever designed for 5 Star. Early Rover V-8s were,
though.
I don' care what they were designed for, I know what they ran best
on ****.

Does that make it a pussy wagon then?

Funny you should say that - I managed to do it in an MG (years ago), but
hardly to be recommended, there's much more room in a rover

--
geoff

On Sat, 6 May 2006 23:45:26 UTC, raden wrote:

Funny you should say that - I managed to do it in an MG (years ago), but
hardly to be recommended, there's much more room in a rover

Not an MG Midget, I trust?

I always laugh at the memory of the Bond Bug. Clearly targeted at the
very young (just passed test) kind of driver - cheap to run, etc. But
also totally useless as a passion wagon, with that great engine bulk
between the seats. Doomed to failure!

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

John Rumm wrote:
The Natural Philosopher wrote:

No standard MG was ever designed for 5 Star. Early Rover V-8s were,
though.


I don' care what they were designed for, I know what they ran best on
****.

Does that make it a pussy wagon then?


Definitely.

In article ,
The Natural Philosopher wrote:
I don' care what they were designed for, I know what they ran best on ****.

Then they were probably well off tune, dear boy. Or it was all in your
mind.


Rough running on a hot day was usually down to fuel evaporation and SU
pumps. Later cars had a constantly circulating fuel rail to help keep
it cool

You really aren't listening are you.

I've been around long enough to know that most who find differences in
petrol are fooling themselves - unless using too low an octane rating for
the design of the engine.

--
*If you ate pasta and anti-pasta, would you still be hungry?

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

On Sat, 6 May 2006 23:15:55 UTC, "Dave Plowman (News)"
wrote:

I've been around long enough to know that most who find differences in
petrol are fooling themselves - unless using too low an octane rating for
the design of the engine.

There is just one difference - the price.

Many years ago I worked on a non self service forecourt. There was a
class of customer who clearly bought 'five star' because they could
afford it, and wanted to flaunt it. I doubt that much has changed.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
I don' care what they were designed for, I know what they ran best on ****.

Then they were probably well off tune, dear boy. Or it was all in your
mind.

Rough running on a hot day was usually down to fuel evaporation and SU
pumps. Later cars had a constantly circulating fuel rail to help keep
it cool

You really aren't listening are you.

I've been around long enough to know that most who find differences in
petrol are fooling themselves - unless using too low an octane rating for
the design of the engine.

Quite right. The old A series high comp engines in midgets and the like
worked better on 5 star, especially once you got them to breathe a bit
better and sorted out the timing a bit.

They WERE designed to work on 5 star. Especially once I had finsished
with em.

They WOULD work on 4, with slightly retarded ignition, to stop them
knocking, but they weren't as good..

The Natural Philosopher wrote:
Quite right. The old A series high comp engines in midgets and the like
worked better on 5 star, especially once you got them to breathe a bit
better and sorted out the timing a bit.

They WERE designed to work on 5 star. Especially once I had finsished
with em.

OK, you say you've done some performance tuning on "A" series engines.
What did this comprise of. Be specific. I don't think you know what
you are talking about, so here's a chance to redeem yourself.

In article ,
The Natural Philosopher wrote:
I've been around long enough to know that most who find differences in
petrol are fooling themselves - unless using too low an octane rating
for the design of the engine.

Quite right. The old A series high comp engines in midgets and the like
worked better on 5 star, especially once you got them to breathe a bit
better and sorted out the timing a bit.

Since I had a two 1275 Midgets, I'm quite well up on that engine. I've
also totally re-built several.

Neither of mine was 'better' on 5 star. Of course if you modify the
engine, you're starting a new ball game. But that's not what you said
originally.

They WERE designed to work on 5 star. Especially once I had finsished
with em.

By 'working' on them it would be possible to make them only suitable for
aviation petrol. Or to run on 2-star. But that's not what they were
designed for - my point.

They WOULD work on 4, with slightly retarded ignition, to stop them
knocking, but they weren't as good.

Mine both ran on standard timing. And didn't pink on 4-star. Perhaps your
timing technique or timing marks were inaccurate? Or perhaps they just
simply needed a de-coke. Also, a slightly weak mixture encourages
detonation.

--
*I like cats, too. Let's exchange recipes.

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

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