[OT] 99 Octane petrol
 

Dave Plowman (News) wrote:
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.

Rubbish, Its the DESIGN of the ENGINE that determnes the compression ratio,

No, its the THICKNESS OF THE HEAD GASKET.

No. It MUST BE THE SHAPE OF THE PISTON.


Don't you love people who are arguing about something, who are just
using different words to say the same thing?

[OT] 99 Octane petrol
 

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..

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

In article
Dave Plowman (News) wrote:
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.


That's all it does - you're talking about swept volume, which is of
course a volume rather than a distance, and even then takes no account
of volumetric efficiency.

[OT] 99 Octane petrol
 

Dave Plowman (News) wrote:
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.

But that isn't what you were talking about, is it. You said:

"The stroke of the piston and the size of the combustion chamber
determine the compression ratio."

They don't, do they.

[OT] 99 Octane petrol
 

The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article Chris Bacon wrote:
Someone else wrote, but the attributions were munged yet again:
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.

Rubbish, Its the DESIGN of the ENGINE that determnes the compression ratio,

True...

No, its the THICKNESS OF THE HEAD GASKET.

True for some engine designs...

No. It MUST BE THE SHAPE OF THE PISTON.

True...


Don't you love people who are arguing about something, who are just
using different words to say the same thing?

You cannot determine the compression ratio from the stroke of the piston
and the size of the combustion chamber, letting the latter include the
thickness of the head gasket (if present), for the same piston shape.

[OT] 99 Octane petrol
 

Rob Morley wrote:
Dave Plowman (News) wrote:
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.

That's all it does - you're talking about swept volume, which is of
course a volume rather than a distance

Erm, "yee-haw", as they are apparently fond of saying in
America. Well Done.

[OT] 99 Octane petrol
 

"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.

[OT] 99 Octane petrol
 

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

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

Chris Bacon wrote:
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article Chris Bacon wrote:
Someone else wrote, but the attributions were munged yet again:
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.

Rubbish, Its the DESIGN of the ENGINE that determnes the compression
ratio,

True...

No, its the THICKNESS OF THE HEAD GASKET.

True for some engine designs...

No. It MUST BE THE SHAPE OF THE PISTON.

True...


Don't you love people who are arguing about something, who are just
using different words to say the same thing?

You cannot determine the compression ratio from the stroke of the piston
and the size of the combustion chamber, letting the latter include the
thickness of the head gasket (if present), for the same piston shape.

You can if you know the bore..

[OT] 99 Octane petrol
 

Sylvain VAN DER WALDE wrote:
"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.

[OT] 99 Octane petrol
 

Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?


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

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

As it's [CR] normally measured, nothing. It was un harang rouge.


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).

At higher RPM, having twin exhaust valves is an improvement over one,
cetrainly. This is reflected in ancient engines which were constructed
with performance in mind, as well as modern ones. However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot).

[OT] 99 Octane petrol
 

The Natural Philosopher wrote:
Chris Bacon wrote:
You cannot determine the compression ratio from the stroke of the piston
and the size of the combustion chamber, letting the latter include the
thickness of the head gasket (if present), for the same piston shape.

You can if you know the bore..

:) !

[OT] 99 Octane petrol
 

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

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

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

[OT] 99 Octane petrol
 

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

[OT] 99 Octane petrol
 

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

[OT] 99 Octane petrol
 

In message , Bob Eager
writes
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?


There are limits ...


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!


--
geoff

[OT] 99 Octane petrol
 

At higher RPM, having twin exhaust valves is an improvement over one,
cetrainly. This is reflected in ancient engines which were constructed
with performance in mind, as well as modern ones. However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot).

Another sweeping generalisation that is only correct 50% of the time.

On any engine there will be some performance limitation areas. You work
on the one that makes the most difference forest. This may be physically
strength - the inability to maintain RPM without exploding, the ability
of the valve gear to work at high RPM or the breathing. The breathing
restrictions may chiefly be the exhaust, or it may be the induction.

Its solely down to the particular design and layout of the engine.

I once asked an F1 engine designer what dictated the way the engines
went together..

"Not much. Short stroke over square because you can rev the **** out of
them without exploding, and that gives us the maximum head area to put
the valves in, then 4 valves because once you get up to 18K RPM you need
all you can get, induction and exhaust.and 4 fits into a round head
better than any other nimber - could use 6 or 8, but then you get
complicated and heavy for marginal gains....then the devil is in the
details of gas flowing the manifolds and getting the valves to work at
that speed, plus the injection and ignition mapping"

No mention of one area being more relevant than another. One accepts
that with turbocharging, inlet design is almost superfluous, as you an
simply increase boost pressure to the cylinders by screwing down the
waste gates etc..

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

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..

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

In article ,
The Natural Philosopher wrote:
However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot).

Another sweeping generalisation that is only correct 50% of the time.


But a true one. Exhaust gases are under highish pressure. Inlet merely -
at best - atomospheric. On the cylinder head and inlet manifold attention
to the inlet tract by reducing restrictions etc that shouldn't be there
but are due to the costs of removing them in manufacture, etc will pay far
more dividends than the same work carried out on the exhaust ports. And
most production cars are already fitted with free (enough) flowing
exhausts.

--
*7up is good for you, signed snow white*

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

[OT] 99 Octane petrol
 

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.

[OT] 99 Octane petrol
 

In message , Chris Bacon
writes
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.

Things can't "comprise of", can they ?



--
geoff

[OT] 99 Octane petrol
 

On Sun, 7 May 2006 14:53:39 UTC, raden wrote:

In message , Chris Bacon
writes
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.

Things can't "comprise of", can they ?

Well, it's Bacon; what did you expect? People are quoting him far too
often, though...!

--
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

[OT] 99 Octane petrol
 

In message , Bob Eager
writes
On Sun, 7 May 2006 14:53:39 UTC, raden wrote:

In message , Chris Bacon
writes
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.

Things can't "comprise of", can they ?

Well, it's Bacon; what did you expect? People are quoting him far too
often, though...!


But note the restraint in my answer ...


--
geoff

[OT] 99 Octane petrol
 

On Sun, 7 May 2006 15:58:14 UTC, raden wrote:

In message , Bob Eager
writes
On Sun, 7 May 2006 14:53:39 UTC, raden wrote:

In message , Chris Bacon
writes
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.

Things can't "comprise of", can they ?

Well, it's Bacon; what did you expect? People are quoting him far too
often, though...!


But note the restraint in my answer ...

Very commendable under such provocation!

--
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

[OT] 99 Octane petrol
 

"Chris Bacon" wrote in message
...
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and
others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?


Hmm! Let's try.

With the piston at B.D.C. (bottom dead centre), at the start of the
compression stroke; the cylinder and combustion chamber will be filled with
an optimum amount of fuel/air mixture. As the piston rises to T.D.C. (top
dead centre), that fuel/air mixture will be compressed to an extent
determined by the stroke/bore ratio of that particular engine and the
capacity of the
combustion chamber. Yes, using a thicker cylinder head gasket (if available)
will reduce the compression ratio; and using a different suitable piston (if
available) will raise that compression ratio.

Comments: The length of the stroke is controlled by the combined design of
the cranckshaft and connecting rod.
The bore size is the diameter of the piston.

Is that enough? I always stand to be corrected.

Sylvain.




snipped

[OT] 99 Octane petrol
 

"Dave Plowman (News)" wrote in message
...
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.


Static timing wasn't everything. Ignition timing "retarding" devices
(distributor vacuum units) often became blocked, or just failed; and the
automatic advance centrifugal weights' spindle could seize up. The weight
control springs could also weaken, or even be the wrong ones fitted
(exchange distributor).

Sylvain.


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

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

[OT] 99 Octane petrol
 

"Chris Bacon" wrote in message
...
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and
others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?


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

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

As it's [CR] normally measured, nothing. It was un harang rouge.


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).

At higher RPM, having twin exhaust valves is an improvement over one,
cetrainly. This is reflected in ancient engines which were constructed
with performance in mind, as well as modern ones.


However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot)

I believe that 2 stroke (racing?) engines were greatly improved (over a
narrow revolutions band) by tuning the exhaust.

Sylvain.

[OT] 99 Octane petrol
 

In article ,
Sylvain VAN DER WALDE wrote:
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.


Static timing wasn't everything. Ignition timing "retarding" devices
(distributor vacuum units) often became blocked, or just failed; and the
automatic advance centrifugal weights' spindle could seize up. The
weight control springs could also weaken, or even be the wrong ones
fitted (exchange distributor).

Absolutely. The advance curve should be checked if pre-detonation is
experienced with the correct static timing. But only if sure the engine
doesn't need a de-coke and the mixture is correct. Also check the
operation of the vacuum unit.

--
*Taxation WITH representation ain't much fun, either.

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

[OT] 99 Octane petrol
 

In article ,
Sylvain VAN DER WALDE wrote:
However, tuning the exhaust system gives lesser results in comparison
with the effects of tuning the input system (by quite a lot)

I believe that 2 stroke (racing?) engines were greatly improved (over a
narrow revolutions band) by tuning the exhaust.

You can tune an exhaust to resonate at certain frequencies. This then
produces an extractor effect. Useful on racing engines with a narrow power
band, but not so much so on a road engine. The same effect is also used on
inlet tracts.

--
*I'm not your type. I'm not inflatable.

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

[OT] 99 Octane petrol
 

raden wrote:
Bob Eager writes
raden wrote:
Chris Bacon writes
The Natural Philosopher wrote:
[engine tuning]
OK, you say you've done some performance tuning on "A" series engines.
What did this comprise of.

Things can't "comprise of", can they ?

Well, it's Bacon; what did you expect? People are quoting him far too
often, though...!

But note the restraint in my answer ...

Can't see how I've upset *you*. Stupid boring non-contributing
*******s perhaps....

[OT] 99 Octane petrol
 

Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and
others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?

Hmm! Let's try.

As the piston rises to T.D.C. (top dead centre), that fuel/air mixture
will be compressed to an extent determined by the stroke/bore ratio of
that particular engine and the capacity of the combustion chamber.

You're sort of getting there, in that you've added the bore as well as
the stroke, which was missing from the quote I included above.

[OT] 99 Octane petrol
 

Sylvain VAN DER WALDE wrote:
[ engine tuning/ compression ratio ]
Comments: The length of the stroke is controlled by the combined design of
the cranckshaft and connecting rod.

Why the *combined* design of the crackshaft and the contorting rod?
Surely just the throw of the crank?

[OT] 99 Octane petrol
 

In message , Chris Bacon
writes
raden wrote:
Bob Eager writes
raden wrote:
Chris Bacon writes
The Natural Philosopher wrote:
[engine tuning]
OK, you say you've done some performance tuning on "A" series engines.
What did this comprise of.

Things can't "comprise of", can they ?

Well, it's Bacon; what did you expect? People are quoting him far too
often, though...!

But note the restraint in my answer ...

Can't see how I've upset *you*. Stupid boring non-contributing
*******s perhaps....


Me - a non-contributor?

To this thread, maybe

and quiet of late because I've been busy saving the world,

but hardly a non contributor

... but then, you're a bit of a newbie and as such, blessed with the
ignorance which goes with it

--
geoff

[OT] 99 Octane petrol
 

In message , Chris Bacon
writes
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Sylvain VAN DER WALDE wrote:
"Chris Bacon" wrote...
Dave Plowman wrote:
The stroke of the piston and the size of the combustion chamber
determine the compression ratio.
[CPB disagreed]
Chris.
You're making a fool of yourself. Just listen to Dave Plowman (and
others).

Above is what DP says determines the CR. Do you *really* agree, or
can you add something to that statement to make it right?

Hmm! Let's try.
As the piston rises to T.D.C. (top dead centre), that fuel/air
mixture
will be compressed to an extent determined by the stroke/bore ratio of
that particular engine and the capacity of the combustion chamber.

You're sort of getting there, in that you've added the bore

I rather think that was your contribution


--
geoff