[xk] 54 Engine rebuild

I’m still not sure about how to deal with the rear seal issue but,
i am thinking of fitting 9:1 pistons from ??? Anyone have
comments, thank You–
Manny 1
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In reply to a message from Manny 1 sent Sun 22 Aug 2010:

Manny,

You can buy new pistons at reasonable prices. AE still
makes them as well as others. If you are going that far you
might consider boring out the cylinders and putting
oversized pistons in.

Wes Keyes–
Wes Keyes
York Maine, United States
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In reply to a message from Manny 1 sent Sun 22 Aug 2010:

Manny
The 9:1 pistons were offered in the 140, when equipped with
the C-type head and 2’’ H8 carbs. Unless you’ve got a C-type
head and 2’’ carbs, the 9:1 pistons serve no useful purpose.
The only thing you may notice is a slightly higher operating
temperature.
Joel–
The original message included these comments:

I am thinking of fitting 9:1 pistons from ??? Anyone have
comments, thank You
Manny 1


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Manny,
My 1954 XK 120 engine number F 2648-9S came with 9: 1 pistons I have had
the car when it was four years old. So some came from the factory that way
and did not have the 2 inch carbs.
Bob.----- Original Message -----
From: “ex jag” jcrprops@sbcglobal.net
To: xk@jag-lovers.org
Sent: Monday, August 23, 2010 8:06 AM
Subject: Re: [xk] 54 Engine rebuild

In reply to a message from Manny 1 sent Sun 22 Aug 2010:

Manny
The 9:1 pistons were offered in the 140, when equipped with
the C-type head and 2’’ H8 carbs. Unless you’ve got a C-type
head and 2’’ carbs, the 9:1 pistons serve no useful purpose.
The only thing you may notice is a slightly higher operating
temperature.
Joel

The original message included these comments:

I am thinking of fitting 9:1 pistons from ??? Anyone have
comments, thank You
Manny 1


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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In reply to a message from bob lockas sent Mon 23 Aug 2010:

Bob
I guess I was misinformed. I stand corrected, sorry.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Joel,
Jaguar offered recommendations and parts for “Tuning Modifications on XK120 Cars for Competition” already in 1951, see story in August 17th, 1951, issue of “Autocar”.
This had suspension upgrades in the form of stiffer springs, torsion as well as semi elliptic, higher lift cams, which later became standard, lightened flywheel, Balanced solid center clutch, “RF” needles for the S.U.s (“RB” with 9:1), distributor 2748 in place of 2747 (retain the 2747 with 9:1), NA 10 Champion plugs (NA12 with 9:1), an upgraded torsional damper for the crank, and dual exhaust.
Pistons for 7:1, 8:1, and 9:1 compression were available.
The article shows 150 B.H.P. for the standard engine with 7:1 pistons and 160 B.H.P. with 8:1 pistons, so right there they claim an increase of 10 B.H.P. for just the compression ratio increase.
With the higher lift cams fitted the engine put out 181 B.H.P. with 8:1 pistons and 190 B.H.P. with 9:1 pistons, - in both cases with rejetted 1¾" carbies. So at least Jaguar felt that there was a significant advantage to higher compression, as long as gasoline of adequate knock resistance was available.
The improved output with higher compression is due to higher thermal efficiency from the combustion process. Higher thermal efficiency indicates that more of the energy in the combustion is converted to mechanical work. When more mechanical work is extracted from the process, less is wasted , and, at least theoretically, less heat should go to the cooling system, which to my way of thinking should make the higher compression ratio engine actually run a smidgen cooler.
Just my two cents worth.
Roar— On Mon, 8/23/10, ex jag jcrprops@sbcglobal.net wrote:

From: ex jag jcrprops@sbcglobal.net
Subject: Re: [xk] 54 Engine rebuild
To: xk@jag-lovers.org
Date: Monday, August 23, 2010, 9:06 AM
In reply to a message from Manny 1
sent Sun 22 Aug 2010:

Manny
The 9:1 pistons were offered in the 140, when equipped
with
the C-type head and 2’’ H8 carbs. Unless you’ve got a
C-type
head and 2’’ carbs, the 9:1 pistons serve no useful
purpose.
The only thing you may notice is a slightly higher
operating
temperature.
Joel

The original message included these comments:

I am thinking of fitting 9:1 pistons from ???
Anyone have
comments, thank You
Manny 1


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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[forums.jag-lovers.org]–
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In reply to a message from Roar Sand sent Mon 23 Aug 2010:

Roar,

Your post provides a nice summary of the XK engine mods which are
often not well spelled out; and eventually led to the adoption of
the the ‘‘S’’ prefix engined cars.

Regarding higher compression resulting in a cooler running engine,
my reading of the literature leads me to believe that a simple
piston change is unlikely to achieve this. While increasing
compression ratios may lead to improved thermal efficiency if
carried across the engine design, a change of this sort is more
often done to increase power output that to enhance efficiency.
This same bugaboo haunts the designers of modern gasoline engines
who have the ability to use compression changes to improve MPG, but
are seemingly forced by marketing considerations to devote their
skills to pursue output increases instead. Apparently the two
objectives lead to quite different, and opposing, engine design
changes .
Karl–
karl
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In reply to a message from Roar Sand sent Mon 23 Aug 2010:

Roar
As I said, I was misinformed. In all honesty though, it’s
tough to notice an increase in performance by gaining 9
horsepower. Your theory on thermal energy and efficiency
makes sense. Although, an increase in compression results in
higher thermal energy from the same amount of potential
energy, due to less waste, which in turn creates higher
mechanical energy. But, more thermal energy means more heat,
doesn’t it? I’m not an engineer, just an ignorant gearhead,
so I may very well be wrong about this too.
Joel–
The original message included these comments:

The article shows 150 B.H.P. for the standard engine with 7:1 pistons and 160 B.H.P. with 8:1 pistons, so right there they claim an increase of 10 B.H.P. for just the compression ratio increase.
With the higher lift cams fitted the engine put out 181 B.H.P. with 8:1 pistons and 190 B.H.P. with 9:1 pistons, - in both cases with rejetted 1�’’ carbies. So at least Jaguar felt that there was a significant advantage to higher compression, as long as gasoline of adequate knock resistance was available.
The improved output with higher compression is due to higher thermal efficiency from the combustion process. Higher thermal efficiency indicates that more of the energy in the combustion is converted to mechanical work. When more mechanical work is extracted from the process, less is wasted , and, at least theoretically, less heat should go to the cooling system, which to my way of thinking should make the higher compression ratio engine actually run a smidgen cooler.
Just my two cents worth.
Roar


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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In reply to a message from ex jag sent Mon 23 Aug 2010:

Joel,

A ‘‘perfect’’ engine would expand the combustion products all the way
back to atmospheric conditions, transforming all of the energy in
the fuel to mechanical work. generally speaking, the heat created
by an engine is the result of inefficiency ; chemical energy made
into heat instead of ‘‘work’’. Of course, the perfect engine does not
exist.

It may help to think abut it like a light bulb; the electricity not
made into light is wasted as heat.

Karl–
The original message included these comments:

mechanical energy. But, more thermal energy means more heat,
doesn’t it? I’m not an engineer, just an ignorant gearhead,


karl
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In reply to a message from Roar Sand sent Mon 23 Aug 2010:

Believe it or not, but in a way, both views are apparently correct.

Whether heat transfer to the cooling system increases, or
decreases, with increase in compression ratio, depends upon the
compression ratio that you start out with.

''Changing the compression ratio of an engine changes the heat
transfer to the coolant very little. Increasing the compression
ratio decreases heat transfer to the coolant slightly, up to about
a 10:1 compression ratio. Increasing the compression ratio above
this value increases heat transfer to the coolant slightly. There
is about a 10% decrease in heat transfer as the compression ratio
is raised from 7:1 to 10:1.

These changes in heat transfer occur mainly because of the
combustion characteristics that change as compression ratio is
raised (e.g. flame speed, gas motion etc.) The higher the
compression ratio, the more expansion cooling will occur during the
power stroke, resulting in cooler exhaust. Compression ignition
(Diesel) engines, with their high compression ratios, generally
have lower exhaust temperatures than spark ignition engines. Piston
temperatures generally increase slightly with increasing
compression ratio.’’

The above is quoted from this textbook:
Reference: ‘‘Engineering Fundamentals of the IC Engine’’, Willard W.
Pulkrabek, 2nd edition, 2004, page 393.

So, evidently, according to this one textbook anyway, if you
increase the compression ratio up to about 10:1, you may actually
experience a decrease in heat transfer to the coolant. Increasing
the compression ratio much above 10:1 apparently increases heat
transfer to the coolant.–
The original message included these comments:

The improved output with higher compression is due to higher thermal efficiency from the combustion process. Higher thermal efficiency indicates that more of the energy in the combustion is converted to mechanical work. When more mechanical work is extracted from the process, less is wasted , and, at least theoretically, less heat should go to the cooling system, which to my way of thinking should make the higher compression ratio engine actually run a smidgen cooler.


Gary Grant S818919DN
Ottawa, Canada
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Joel,
Your comment posted while I was busy writing.
On the subject of energy, - as you mentioned, there is only so much potential energy, which is represented by the amount of fuel in the incoming charge. So if the incoming charge is not altered, the amount of potential energy you can get out of it, does not change.
To my way of thinking then, when you extract more mechanical work out of that charge by improving thermal efficiency, there should be less energy in the form of heat lost to exhaust gases and cooling system.
If I could find it, I would give you quote and page number from Dr. John B. Heywood’s “Internal Combustion Engine Fundamentals”. I know it’s in there, but I don’t remember where. That’s “Oldtimers’ Disease” for you.
Roar— On Mon, 8/23/10, ex jag jcrprops@sbcglobal.net wrote:

From: ex jag jcrprops@sbcglobal.net
Subject: Re: [xk] 54 Engine rebuild
To: xk@jag-lovers.org
Date: Monday, August 23, 2010, 10:48 PM
In reply to a message from Roar Sand
sent Mon 23 Aug 2010:

Roar
As I said, I was misinformed. In all honesty though, it’s
tough to notice an increase in performance by gaining 9
horsepower… Your theory on thermal energy and efficiency
makes sense. Although, an increase in compression results
in
higher thermal energy from the same amount of potential
energy, due to less waste, which in turn creates higher
mechanical energy. But, more thermal energy means more
heat,
doesn’t it? I’m not an engineer, just an ignorant
gearhead,
so I may very well be wrong about this too.
Joel

The original message included these comments:

The article shows 150 B.H.P. for the standard engine
with 7:1 pistons and 160 B.H.P. with 8:1 pistons, so right
there they claim an increase of 10 B.H.P. for just the
compression ratio increase.
With the higher lift cams fitted the engine put out
181 B.H.P. with 8:1 pistons and 190 B.H.P. with 9:1 pistons,

  • in both cases with rejetted 1¾’’ carbies. So at
    least Jaguar felt that there was a significant advantage to
    higher compression, as long as gasoline of adequate knock
    resistance was available.

The improved output with higher compression is due to
higher thermal efficiency from the combustion process.
Higher thermal efficiency indicates that more of the energy
in the combustion is converted to mechanical work.
When more mechanical work is extracted from the process,
less is wasted , and, at least theoretically, less heat
should go to the cooling system, which to my way of thinking
should make the higher compression ratio engine actually run
a smidgen cooler.
Just my two cents worth.
Roar


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Karl,
Yeah, every engine design is a compromise, and where the priorities are put will depend on market forces.
Designers strive to shape the combustion chamber and the ports, leading to and from it, to be tolerant of high compression in the interest of both power and fuel efficiency. And especially in the case of the ports, what benefits economy, does often work against power, may be not torque in the usual working range, but definitely ultimate top end.
Tolerance of high compression depends on many factors, of which swirl, tumble, and temperature of the combustion chamber surfaces are but a few.
This day and age emissions also play a very large role in the compromises. As an example, high compression is good for power and fuel economy, but it is bad for the formation of NOX, - one reason there are so few Diesel passenger cars available in this country, as we have very tough limits on NOX emissions relative to Europe.
I agree that simply a piston change to achieve a higher compression ratio, will not cure the overheating tendencies of an XK, but I think that incrementally it is a step in the right direction.
Roar— On Mon, 8/23/10, karl klkirkman@aol.com wrote:

From: karl klkirkman@aol.com
Subject: Re: [xk] 54 Engine rebuild
To: xk@jag-lovers.org
Date: Monday, August 23, 2010, 11:19 PM
In reply to a message from Roar Sand
sent Mon 23 Aug 2010:

Roar,

Your post provides a nice summary of the XK engine mods
which are
often not well spelled out; and eventually led to the
adoption of
the the ‘‘S’’ prefix engined cars.

Regarding higher compression resulting in a cooler running
engine,
my reading of the literature leads me to believe that a
simple
piston change is unlikely to achieve this. While increasing

compression ratios may lead to improved thermal efficiency
if
carried across the engine design, a change of this sort is
more
often done to increase power output that to enhance
efficiency.
This same bugaboo haunts the designers of modern gasoline
engines
who have the ability to use compression changes to improve
MPG, but
are seemingly forced by marketing considerations to devote
their
skills to pursue output increases instead. Apparently the
two
objectives lead to quite different, and opposing, engine
design
changes .
Karl

karl
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In reply to a message from karl sent Tue 24 Aug 2010:

My two cents:

If the same amount of air/fuel mixture gets compressed to a
higher level, as in 9:1 compared to 8:1, then both the
pressure and the temperature of the mixture is going to be
higher at the end of the stroke. That’s the ideal gas law.
(I realize that this mixture isn’t ‘‘ideal’’ but that means
only corrections, not fundamental changes.)

If that fixed amount of mixture is then burned in a smaller
space than at the lower CR it will again result in both the
temperature and pressure being higher than at the lower CR.
In fact, what I’ve always thought is that it’s that higher
pressure that supplies the force on the piston top to
generate more power than at lower CR’s.

Then the piston moves down to another
pressure/volume/temperature condition. If all of this
happened instantaneously no heat would be transferred to the
engine or anywhere else and the conditions at the end state
could be calculated pretty exactly. But it doesn’t happen
instantaneously, and since the temperature in the combustion
chamber must be higher at a higher CR, then there must be
some increase in heat transfer from the gases to the head
and cylinder walls, and maybe the exhaust gas temperature is
going to be higher too, depending on how much heat is
actually lost to the block and head.

I realize that there are complications- like I don’t know
what happens to the heat of combustion as temperature and
pressure change. But I can’t see how a higher CR can lead
to lower engine temperatures, and neither can I see how
these higher temperatures can lead to better thermal
efficiency, since any heat lost to the cooling system or to
the exhaust gas is a loss of efficiency.

But, then again, I’ve learned a lot from this list and maybe
this is another opportunity.

Bruce Wright
#674699
Bruce Wright XK120 OTS #674699
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In reply to a message from karl sent Tue 24 Aug 2010:

If anyone is interested, J.B. Heywood explains it a little more in
his textbook ‘‘IC Engine Fundamentals’’, page 703.

He also agrees that above 10:1, increasing compression ratio
transfers more heat to the coolant. Below 10:1, increasing
compression ratio decreases heat transfer to the coolant.

Apparently increasing compression ratio (at constant throttle
opening) changes the gas properties of the intake charge such that:

a) cylinder gas pressures and peak burned gas pressure both
increase. This would be due to the gas being compressed more
before, and during, burning, as compared to a lower compression
ratio. The more a gas is compressed, the more its temperature goes
up.
b)gas motion increases, because of increased turbulence, causing
better atomization and mixing and more complete combustion
c) combustion is faster, because of increased charge density. The
charge molecules are compressed closer to one another thus
increasing flame speed
d)the surface area/volume ratio of the combustion chamber, when the
piston is at TDC, increases, thus allowing more heat of combustion
to transfer to the cylinder head and coolant
e) the gas temperature late in the expansion stroke and during the
exhaust stroke is reduced. This is because, the more a gas expands,
the more its temperature decreases. With a higher compression
ratio, the gas expands more than with a lower compressuion ratio,
during the expansion and exhaust strokes.

The above effects a,b,c and d tend to increase heat transfer to the
coolant, while effect e tends to decrease heat transfer to the
coolant.

Apparently for compression ratios above 10:1, when you increase the
compression ratio, effects a,b,c and d are more important and
overwhelm the effect e) and heat transfer to the coolant increases.

And for compression ratios below 10:1, when compression ratio is
increased, the gas expansion cooling effect e) is more important
and overwhelms the other effects, and heat transfer decreases.

He even explains that generally head and exhaust valve temps
decrease with increasing compression ratio, due to lower expansion
stroke and exhaust stroke temperatures which cool off the valves
better. Piston and sparkplug temps increase, due to higher peak
combustion temperatures at higher compression ratios.

Once the compression ratio is increased enough to cause knocking,
the very high gas pressures and temps result in very much localized
huge increase in heat transfer to the piston and head, eventually
causing much damage, because the heat cannot be transferred away
fast enough.–
Gary Grant S818919DN
Ottawa, Canada
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Gary,
Apparently Heywood agrees with Pulkrabek, because I do remember reading that above 10:1 compression the trend reverses. Why this is so is unclear to me.
Roar> Whether heat transfer to the cooling system increases, or

decreases, with increase in compression ratio, depends upon
the
compression ratio that you start out with.

''Changing the compression ratio of an engine changes the
heat
transfer to the coolant very little. Increasing the
compression
ratio decreases heat transfer to the coolant slightly, up
to about
a 10:1 compression ratio. Increasing the compression ratio
above
this value increases heat transfer to the coolant slightly.

Gary,
Thanks for the reference to page 703 in Haywood.
Roar— On Tue, 8/24/10, Gary Grant grant3@sympatico.ca wrote:

From: Gary Grant grant3@sympatico.ca
Subject: Re: [xk] 54 Engine rebuild
To: xk@jag-lovers.org
Date: Tuesday, August 24, 2010, 2:29 PM
In reply to a message from karl sent
Tue 24 Aug 2010:

If anyone is interested, J.B. Heywood explains it a little
more in
his textbook ‘‘IC Engine Fundamentals’’, page 703.

He also agrees that above 10:1, increasing compression
ratio
transfers more heat to the coolant. Below 10:1, increasing

compression ratio decreases heat transfer to the coolant.

Apparently increasing compression ratio (at constant
throttle
opening) changes the gas properties of the intake charge
such that:

a) cylinder gas pressures and peak burned gas pressure both

increase. This would be due to the gas being compressed
more
before, and during, burning, as compared to a lower
compression
ratio. The more a gas is compressed, the more its
temperature goes
up.
b)gas motion increases, because of increased turbulence,
causing
better atomization and mixing and more complete combustion
c) combustion is faster, because of increased charge
density. The
charge molecules are compressed closer to one another thus

increasing flame speed
d)the surface area/volume ratio of the combustion chamber,
when the
piston is at TDC, increases, thus allowing more heat of
combustion
to transfer to the cylinder head and coolant
e) the gas temperature late in the expansion stroke and
during the
exhaust stroke is reduced. This is because, the more a gas
expands,
the more its temperature decreases. With a higher
compression
ratio, the gas expands more than with a lower compressuion
ratio,
during the expansion and exhaust strokes.

The above effects a,b,c and d tend to increase heat
transfer to the
coolant, while effect e tends to decrease heat transfer to
the
coolant.

Apparently for compression ratios above 10:1, when you
increase the
compression ratio, effects a,b,c and d are more important
and
overwhelm the effect e) and heat transfer to the coolant
increases.

And for compression ratios below 10:1, when compression
ratio is
increased, the gas expansion cooling effect e) is more
important
and overwhelms the other effects, and heat transfer
decreases.

He even explains that generally head and exhaust valve
temps
decrease with increasing compression ratio, due to lower
expansion
stroke and exhaust stroke temperatures which cool off the
valves
better. Piston and sparkplug temps increase, due to higher
peak
combustion temperatures at higher compression ratios.

Once the compression ratio is increased enough to cause
knocking,
the very high gas pressures and temps result in very much
localized
huge increase in heat transfer to the piston and head,
eventually
causing much damage, because the heat cannot be transferred
away
fast enough.


Gary Grant S818919DN
Ottawa, Canada
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We seem to be debating the characteristics of combustion and it’s by
products with the increases in compression without factoring in the
energy and perhaps the heat necessarily expended to do it!

IMHO, It might be a thermal “wash” after all is measured and calculated.

Something to think about: Does the engine run hotter with the later 4
ring pistons (4th below the gudgeon pin) than with the originals? Run
hotter with an overbore?

Regards,

Rick____________________________________________________________
Obama Urges Homeowners to Refinance
If you owe under $729k you probably qualify for Obama’s Refi Program
http://thirdpartyoffers.juno.com/TGL3141/4c7429a027de6145e23m03vuc

In reply to a message from Gary Grant sent Tue 24 Aug 2010:

Well, there you are. I did learn something! Thanks to Gary
Grant and J. B. Heywood.

I’m still having a little trouble understanding why the
bottom-of-the-stroke temperature is lower. That implies
it’s a ‘‘path’’ process, not a ‘‘state’’ process. Guess I’d
better read the book.

Bruce Wright
#674699
The original message included these comments:

If anyone is interested, J.B. Heywood explains it a little more in
his textbook ‘‘IC Engine Fundamentals’’, page 703.


Bruce Wright XK120 OTS #674699
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A belated comment on this thread.

According to Anders Clausager - JDHT - book on XK140/XK150 in detail, of the
8900 or so XK140 engines made all were 8:1 cr EXCEPT approximately 80 were
built/supplied with 7:1 cr and approximately the same 80 were built/supplied
with 9:1 cr.

The determining factor being availability of fuel quality but there being no
direct correlation between whether C-Type head or A-Type head was fitted,
and whether H8 or H6 carburetters were fitted. Indeed there were C-Type
headed engines supplied with 7:1 cr. The probability was that many 9:1 cr
engines may well have been ordered where owner had racing intensions with
availability of high-octane fuel and thus most likely to have also specified
C-Type Head and H8 carburetters, but no direct correlation that you can say
all 9:1 cr engines did in fact also have H8 carburetters fitted, and
certainly no evidence that this was the case - quite the opposite in fact as
per Bobs car below.

But fuel remains the main problem today regarding use of 9:1 pistons or not,
and certainly for a road car I would most definitely NOT modify an existing
8:1 cr XK to become 9:1 cr. The theoretical 5-10 hp gain is unlikely to be
achieved, if in fact a driver could actually tell anyway, unless all other
aspects of engine and driveline condition were in 100% as-new condition and
state-of-tune, but they would constantly have issues with obtaining the 100
octane fuel required to optimise their 9:1 cr needs.

In deed, in Australia, where 9:1 cr was most common for E-Types, I regularly
advise people rebuilding their engines to consider rebuilding with 8:1 cr
pistons so they will have everyday useable performance and fuel
availability.
Thos who have any racing aspirations have many options over and above 8:1
versus 9:1 pistons to realise any power gains, and more time is gained on a
track with handling/braking modifications than you get with a few extra
horsepower anyway.

My bottom line is if you want to use your XK for road use - stay with 8:1 cr
regardless of everything else. If you want to use your XK regularly and
more competively for track/racing purposes then do whatever you are
comfortable with, and having said that - same comment re H8 carburetters.
Only benefit of fitting H8 carburetters onto a road-use XK is the wow-factor
and bragging rights when you open the bonnet. There is no performance
benefit at all and low/medium rpm typical of road use, but you do have
constant driveability/tuning/fuel-leakage problems to contend with. If you
want to race, or drive often at the red-line on the road, then yes, there
are a few extra horsepower available to compensate for the normal use
down-side.

Roger Payne - XK140MC OTS; E-Type 4.2 S.1 OTS; DSV8.
Canberra.-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
bob lockas
Sent: Tuesday, 24 August 2010 1:36 AM
To: xk@jag-lovers.org
Subject: Re: [xk] 54 Engine rebuild

Manny,
My 1954 XK 120 engine number F 2648-9S came with 9: 1 pistons I have had

the car when it was four years old. So some came from the factory that way
and did not have the 2 inch carbs.
Bob.

----- Original Message -----
From: “ex jag” jcrprops@sbcglobal.net
To: xk@jag-lovers.org
Sent: Monday, August 23, 2010 8:06 AM
Subject: Re: [xk] 54 Engine rebuild

In reply to a message from Manny 1 sent Sun 22 Aug 2010:

Manny
The 9:1 pistons were offered in the 140, when equipped with
the C-type head and 2’’ H8 carbs. Unless you’ve got a C-type
head and 2’’ carbs, the 9:1 pistons serve no useful purpose.
The only thing you may notice is a slightly higher operating
temperature.
Joel

The original message included these comments:

I am thinking of fitting 9:1 pistons from ??? Anyone have
comments, thank You
Manny 1


ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Roger,
I am a little confused by your statement:

The theoretical 5-10 hp gain is unlikely to be

achieved, if in fact a driver could actually tell anyway,
unless all other
aspects of engine and driveline condition were in 100%
as-new condition and
state-of-tune, but they would constantly have issues with
obtaining the 100
octane fuel required to optimise their 9:1 cr needs.

The report in Autocar, previously mentioned, claimed that 85 to 90 octane fuel was needed for 9:1 compression ratio XK engimes, and you say 100.
Granted, neither are specific as to whether the numbers represent “Motor” or “Research” method, however, my engine with 9:1 and “B” head seems to run nicely on our unleaded premium fuel, which runs at 93 or 94 R+M/2 octane.
Admittedly I have not checked to see what basic spark advance is set at by the shop, but I do know that the carbies are jetted on the rich side, based on the fact that I have yet to achieve significantly over 13 MPG, or 18 liters per 100 km.
Regards,
Roar