[v12-engine] High-Compression Flat Head?

When the H.E. was developed, it had a “fireball” combustion chamber,
11.5:1 compression (12.5:1 in Europe), and a timing system that
provided full advance at light throttle but much less advance at full
throttle to avoid detonation with such high compression ratios. The
fuel economy of the XJ-S improved markedly, although reportedly the
gains were much smaller for cars driven hard. This makes sense:
having the high CR combined with full advance at light throttle
should result in impressive fuel economy.

So, here’s my question: what did the fireball combustion chamber have
to do with it? If you took a pre-H.E. flat head engine, installed
pistons with a smaller pocket in the middle to achieve a compression
ratio of 11:1 or more, and installed the H.E. distributor with its
advance curves that provide full advance at light throttle but very
little advance at heavy throttle to avoid detonation, wouldn’t you
also get excellent fuel economy? And good power – as with the H.E.,
the timing may be retarded at WOT, but the compression ratio is so
high that it’s a wash. Plus, you no longer have the pocketed exhaust
valve to limit flow at high power.

– Kirbert

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In reply to a message from Kirbert sent Mon 13 Mar 2006:

Kirbert,
I’ll bet Roger will have to end up stepping in to completely answer
that question, but based on his comments of the past, the
compression ratio was only one part of the package that improved
gas mileage. (Remember too, they cheated and changed the
differential ration to 2.88) Optimal flame propagation will
increase pressures without promoting detonation. Turbulance also
allows reliable burning of a more rarified mixture. It seems to me
that those two together would allow the same power to be gained
from a lighter throttle using less mixture.
In addition, I’m not sure you could safely get the same benefit
from a high-compression flat head with HE timing. My understanding
is that the fireball head creates a more controlled rise in
pressure as the burn spreads, reducing chances for detonation. The
safety margin for detonation on a high-compression flat-head engine
with HE timing might be compromised. It might go unnoticed for
quite some time until that hot day after gentle driving where you
punch it…and then wonder what went wrong.

Tony Evans Omaha, NE
91 V-12 XJ-S Convertible–
tonysxjs
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If I recall from what Roger wrote, the problem with the flat head was
charge stagnation at low speed operation - or where a road car would
spend most of its time, and that lead to incomplete combustion. The HE
introduced the swirl and turbulence to provide complete combustion,
while raising the CR increased thermal efficiency.

Roger did also say that they were able to burn lean mixtures at high
compression ratios, which was part of the plan to increase fuel
efficiency, whereas the lean mixture wouldn’t burn correctly at lower CR’s.

Craig

Kirbert wrote:

.

So, here’s my question: what did the fireball combustion chamber have
to do with it?

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So, here’s my question: what did the fireball combustion chamber have
to do with it? If you took a pre-H.E. flat head engine, installed
pistons with a smaller pocket in the middle to achieve a compression
ratio of 11:1 or more, and installed the H.E. distributor with its
advance curves that provide full advance at light throttle but very
little advance at heavy throttle to avoid detonation, wouldn’t you
also get excellent fuel economy? And good power – as with the H.E.,
the timing may be retarded at WOT, but the compression ratio is so
high that it’s a wash. Plus, you no longer have the pocketed exhaust
valve to limit flow at high power.

– Kirbert

Isn’t this similar to what Roger Bywater’s paper investigated? Moving the
May combustion chamber design into the piston?------------
Robert
87XJ-SC
73XJ12HE

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Craig Talbot wrote:

If I recall from what Roger wrote, the problem with the flat head was
charge stagnation at low speed operation - or where a road car would
spend most of its time, and that lead to incomplete combustion. The HE
introduced the swirl and turbulence to provide complete combustion,
while raising the CR increased thermal efficiency.

OK, so the CR and related ignition timing were intended to address
fuel economy issues while the fireball head was to address another
issue, incomplete combustion at low speeds, which probably hurt fuel
economy but are more likely an emissions issue?

Still, if this is the case, perhaps there’d be value in going with a
flat head and >11:1 CR plus some interesting design in the piston
crowns to help the stagnation issue. I think you’re gonna be buying
new pistons anyway, so what we’re saying here is that people with pre-
H.E.'s could replace the pistons and the distributor and achieve
significantly better fuel economy with no penalty, and possibly even
an improvement, in performance.

Maybe, for example, if the crown of the piston were merely sloped
gently so that when it approaches the flat head it tends to pinch
slightly at one side and drive the charge towards the other side.
It’d be nowhere near the effect of the swirl chamber in the fireball
head, but maybe it’d be enough to minimize the issue of incomplete
combustion to acceptable levels.

Roger did also say that they were able to burn lean mixtures at high
compression ratios, which was part of the plan to increase fuel
efficiency, whereas the lean mixture wouldn’t burn correctly at lower
CR’s.

Yeah, but then the whole lean mixture issue became moot because they
had to run closed-loop to minimize NO emissions. You don’t need the
fireball head to run closed-loop.

In fact, just exactly what fuelling system you’d use with this high-
CR flat head I’m proposing would be another interesting question. If
you just tossed a MegaSquirt in there and trimmed it properly you’d
probably be OK, but it’d be interesting to see how well it’d work if
you just tossed an H.E. Digital P system in there and ran it. With
CR and ignition timing comparable to the H.E., the H.E. fuelling maps
might work fine. As I understand it, the biggest difference between
the pre-H.E. and H.E. fuelling is that the Digital P is far superior
to the D Jetronic in terms of accuracy (not to mention the capacity
for closed-loop operation). Of course, you’d have to bring the
pressure regulators, rail, and injectors along, since they’re
different than the D Jetronic injectors.

Which, of course, brings us to the idea of doing this whole thing
from the other way around. Start with an H.E. 5.3 car, replace the
heads with flat heads and a new set of pistons (you might even be
able to modify the existing pistons a bit, or perhaps install really
thick head gaskets to keep the CR within reasonable limits), and run
it. What you’d end up with, hopefully, would be a car with the fuel
economy of an H.E. 5.3 but more performance at the top end. One big
question might be whether the car would ever pass emissions.

– Kirbert

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In reply to a message from Kirbert sent Tue 14 Mar 2006:

Yeah…Interesting thought. It appears that the burning of the
fuel/air is dependant on, among other things, turbulence. The
theory seems to be that the highly turbulent frame front leads to
an increased surface area of the frame front which allows more
mixture to burn because more is exposed to the flame front. Makes
sense. So maybe you could ‘‘indent’’ the piston crown with
the ‘‘fireball’’ shape and have a flat head.
I think if you’re after extra power on the Jag V12 then instead of
spending time going down this path you’d be better off spending
your time digging a large hole in the back lawn and shovelling
dollar notes into it!!!(Humour.)

Matt Furness–
The original message included these comments:

Maybe, for example, if the crown of the piston were merely sloped
gently so that when it approaches the flat head it tends to pinch
slightly at one side and drive the charge towards the other side.
It’d be nowhere near the effect of the swirl chamber in the fireball
head, but maybe it’d be enough to minimize the issue of incomplete
combustion to acceptable levels.


MattFurness
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So maybe you could ‘‘indent’’ the piston crown with
the ‘‘fireball’’ shape and have a flat head.

Funnily enough, Roger was recently talking about this.

Gordan

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On Tue, 14 Mar 2006, MattFurness wrote:

In reply to a message from Kirbert sent Tue 14 Mar 2006:

HEY! Kirbert; odd that you bring up the sloped piston crown,
a guy named Smokey Yunick in Daytona bch. experimented with
just that, back around 79-82, but he had two slopes, I think
he called it the YIN-YANG chamber. again it was about
introducing more turbulence, wish I had the money to
experiment. anywho its another lost idea unless sombody trys
it again.

RON___–
ronbros
daytona fl. usa, United States
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ronbros wrote:

HEY! Kirbert; odd that you bring up the sloped piston crown

Y’know, thinking about it more, I think just the increase in CR might
be a big help here. I can see things getting stagnant in the
combustion chamber when the compression is only 7.5:1 or whatever,
while just going to 11:1 without any other changes will probably
improve the flame propagation characteristics.

– Kirbert

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In reply to a message from Kirbert sent Wed 15 Mar 2006:

good points, I think that the main issue is maintaining proper
turbulance to keep that tiny amount of fuel atomized as any petrol-
combustion motor is not efficient under light throttle aplications
and due to our v-12’s large number of cylinders, each one is only
receiving a small amount of fuel under many comonly used throttle
positions. I have corresponded with Rob Beere and actually had a
similar design used for my re-build last year when I had my custom
pistons machined; these pistons are shaped in such a way to allow
the use of the better-flowing flat head and still have the fuel
efficiency and safety of even flame burn and fuel atomization. Rob
sells some great pistons according to a fellow I met from red deer
alberta at a real estate confrence had ordered these and was quite
happy. I have never used these pistons and I have no affiliation
with the co…

Snowing in SA today, gotta leave her at home :(.

www.rob-beere-racing.co.uk–
Regards, Keith Cox, 1987 Canadian VDP V-12
Salmon Arm, British Columbia, Canada
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In reply to a message from V-twizzle sent Fri 17 Mar 2006:

Atomization; that is exactly why I went to 10-1 pistons and
Honda fuel injectors,now run 43psi fuel pressure at idle
much finer fuel droplets equals better atomization. --BUT;(I
hope this doesnt reveal my age) the flat chamber, the 1st
ones I remember was around 1949-50 I had an old 31 chevy 6,
took the head off one day ,nothin to do just bored, looked
at chamber and noticed the exhuast valve way down in this
funny pocket, I absolutly did not no what I was doing. it
perked my interest got out my books and Chevy started that
design in 1928 on there 1st 6 cylinder and carried it all
the way to 1962. If you ever get the chance to pull a head
off the early Corvette in-line 6 you will see the the so
called MAYS type chamber, the engineering was for the same
principles, induced turbulance. any way if you wanted a fast
Chevy before 1955 you would try to find an aftermarket
head,called a WAYNE head it had a flat chamber and cross
flow manifolds. I guess there isnt anything new, just
reapplication of old ideas. but I do like some of this new
tech, like direct chamber injection , turbocharging tech,
and what about AUDI winning SEBRING with a DIESEL. now thats
new technology. electronics are taking things right out of
sight!! long live the TRANSISTOR thanks again RON–
ronbros
daytona fl. usa, United States
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In reply to a message from tonysxjs sent Mon 13 Mar 2006:

Just a thought if this thread keeps going, the PRICE of
PRE- HE heads are going up- in value. RON–
ronbros
daytona fl. usa, United States
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Ron,

Does that mean that I might eventually recover my maintenance costs
by parting out?

Just kidding. It’s too painful to consider. MY HEADS ARE NOT FOR SALE!

Ed Sowell
1976 XJ-S
http://www.efsowell.us/ed/myJag.html

Just a thought if this thread keeps going, the PRICE of
PRE- HE heads are going up- in value. RON

ronbros

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In reply to a message from Ed Sowell sent Tue 21 Mar 2006:

HI! ED SOWELL:: this is not to be derogatory about these
wonderfull JAG V-12s, I bought 4 unit engines from a scrap yard
for $50. each all flat head types, so I have some parts to
sell.I could not have the courage to let them go to the
smelter. ALL that I know dont amount to much, when it comes
to REALITY. anyway im going to a car auction this weekend,
let us see what a rare78 JAGUAR XJS ROADSTER, hi-performance
will sell for. thanks RON–
ronbros
daytona fl. usa, United States
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I really wasn’t offended, Ron. Just making a joke.

I know exactly what you mean about wasting any piece of
one of these cars. A year or so ago I helped a former list
member sell off his collection of miscellaneous parts
after selling his car. Got rid of most of them, sometimes
shipping seemingly useless little pieces to distant lands
in eBay transactions whereby only FedEx made any money.
The parts I couldn’t sell are still in the garage, even though
they won’t fit my car and no one wanted them.

Ed Sowell
1976 XJ-S
http://www.efsowell.us/ed/myJag.html

HI! ED SOWELL:: this is not to be derogatory about these
wonderfull JAG V-12s, I bought 4 unit engines from a scrap
yard for $50. each all flat head types, so I have some parts
to sell.I could not have the courage to let them go to the
smelter. ALL that I know dont amount to much, when it comes
to REALITY. anyway im going to a car auction this weekend,
let us see what a rare78 JAGUAR XJS ROADSTER, hi-performance
will sell for. thanks RON

ronbros

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Yeah, that’s where I’ve been this past week, down in Tampa visiting
relatives, Sebring, and Randy Wheelis. I’m afraid I tortured Wheelis
pretty badly, baking him in the sun, walking his a** off, then
freezing him to the point where I think he ended up wearing all the
clothes he had along on the trip.

ronbros wrote:

but I do like some of this new
tech, like direct chamber injection , turbocharging tech,
and what about AUDI winning SEBRING with a DIESEL. now thats
new technology.

Well, not really, although they’re certainly promoting it as such.
The rules for that particular racing class (LeMans Prototype 1, or
LMP1, or just P1) stipulate that all the air the engine breathes must
be drawn through a pair of particular size openings. This
fundamentally limits the HP to about 650, regardless of the size
engine used. For example the Audi R8 used a dual-turbo’ed V8 of
something like 4.5 litres, the Panoz used a much larger naturally-
aspirated pushrod V8, and some competitors go the other way with
fairly small engines, even 4-bangers, with gobs of turbo boost.

Apparently the limit remains at about 650 HP regardless of gasoline
vs. diesel, meaning that combusting the same amount of air with
either fuel releases about the same amount of energy. Of course, to
get the same HP with a diesel requires that the diesel engine be
larger than the gasoline engine had been. The Audi R10 has a dual-
turbo’ed V12 of 5.5 litre.

So, why did Audi go with diesel? Officially because the diesel
engine, while still limited to the same 650 HP as the gasoline engine
was, will provide them something like 840 ft-lb of torque. While
that’d appear to be a very good reason, remember that HP is what
makes a race car fast, and more torque with the same HP means less
rpm which means all you’re doing is changing drive ratios. I suspect
the real reason for the switch to diesel is to promote diesel, which
is already very popular in Europe but hasn’t caught on here in the US.

Compared to the V8 of the R8, the 120-degree V12 in the R10 is lower
and longer. This allowed the whole rear end of the car to appear
more compact, as though it had a smaller engine under there rather
than a larger one.

BTW, much was touted about the diesel fuel itself. The Audi
supposedly didn’t run on conventional diesel fuel but rather a new
blend that burns cleaner. Word is that it was actually 90% the
regular stuff mixed with 10% something else.

The Audis weren’t the only diesel cars entered. The entry list
included another P1 car with a diesel engine. It didn’t start the
race, though. I have no idea what the story was there.

Whatever, the Audi R10 is very fast indeed – just as the Audi R8
was, and in exactly the same fashion. If you’ve never seen these
racing Audis at work, you are missing something indeed. They are
blindingly fast while being totally silent. You can blame the
silence on the turbos, but one hastens to point out that there are
LOTS of turbos out there and all the others are quite noisy. The
Audis are completely silent, on throttle or off.

They also corner like nobody’s business. All the other cars look
like they’re racing, while the Audis seem like they’re out for a
pleasant afternoon drive. All the sounds you hear other cars making -

  • the grinding sound of the brakes approaching the corner, the
    scrubbing sounds of the tires digging in going through the corner,
    the knocks and rattles as the wheels bounce over rough surfaces, the
    whirr of the gears, all these sounds are completely absent in the
    Audis. The car moves like a ghost around the track – a very, very
    fast ghost.

Only one Audi finished, and it led wire-to-wire. The other Audi R10
had mechanical troubles during practice the day before and the team
stayed up all night, with curtains around the work area for secrecy,
taking the engine out and doing something with it. It started the
race but quickly retired. Reported problem was overheating, but
there’s no assurance that they’d tell us the real reason.

BTW, the Porsche P2 prototypes made their debut at Sebring as well.
They didn’t do too well in the final standings, but they impressed
all who saw them. Totally unlike the Audis, they have sound and fury
to spare. They were only a click slower than the Audis despite being
in a slower class.

They had problems right off, though. Both had failures in the first
hour, electrical is what was reported, that put them in the pits for
a while. From then on it was a game of catch-up. One was so far
back that it was largely hopeless, and when it broke down later
(reportedly a broken halfshaft) it made little difference to the
standings. But the other worked its way back up into the running,
catching back up to the back end of the class leader with each yellow
flag and then passing him to unlap himself when the course went green
again. In this fashion, he eventually managed to regain the class
lead. With 20 minutes to go in the 12 hours, he suddenly failed and
pulled off the side of the road. The official explanation was
another broken halfshaft, but those who were standing on that corner
say that was hogwash, all the lights suddenly went out on the car as
it went past.

Other minor reports:

On Turn 10, the spectators can stand around the inside of the turn,
but there’s no spectator access to the outside. Outside the turn
there’s perhaps 50 yards of open grass for runoff, then a wall with
stacks of tires in front of it. There was a corner worker standing
on top of the wall. The guy tripped and fell headfirst into a stack
of tires, getting himself jammed with only his feet sticking out the
top – in plain view of a couple hundred spectators. They had to
stop the race in order to get help to him, since it wasn’t possible
to get there without crossing the track. In the resulting melee, an
ambulance came very close to colliding with the only Ferrari in the
race, as the Ferrari was circulating under a full course caution but
didn’t realize that the ambulance planned to drive straight off the
corner rather than following the pavement around the corner.

Some guy driving a P2 car was going around the long sweeper leading
to the hairpin when his engine broke. He coasted off the inside of
the curve and came to a stop in a nice, safe location up against the
guard rail – just ten feet or so from where all the spectators were
partying on the other side of the fence. He was sitting there
dejected when some party animal tossed him a beer over the fence.
Whatta they gonna do, disqualify him for drinking? He ended up
sitting there in his car for HOURS, guzzling beer after beer and
watching the race grind on. He ended up with a neat circle of beer
cans surrounding his dead car, most empty but some full due to the
poor aim of the tossers. When the race ended, the wrecker came out
and towed him around the track to the pits, with him waving joyously
to the crowd.

The GT2 class is normally ruled by Porsches, which is why my choice
to win is always “anyone but Porsche”. Their competition over the
past few years has included the Panoz Esperante (front-engine RWD
V8), something called a Stryker, and a couple of models of Ferrari.
The Strykers are always slow, although this year they proved stout
and ran consistently start to finish. One Panoz and a Ferrari were
giving it go, though, and ended up swapping the class lead back and
forth between them for hours, relegating the endless succession of
Porsches to no better than third. The Ferrari seemed to have the
edge by a hair. Every now and then, both the Panoz and the Ferrari
would pit together, allowing a Porsche to lead for a few laps, then
it would pit and we’d be off to the races with the Panoz and Ferrari
again. The Panoz conveniently lost his rear bumper somewhere halfway
through the race, probably giving him a weight benefit. Anyhow,
somebody screwed up with less than an hour to go, and the Ferrari
ended up back in 3rd with no chance of improving that position. The
Panoz went on to win the class, some Porsche second, the Ferrari
third.

The GT1 class had two Corvettes, two Aston Martins, and two Saleens
entered. All six cars finished. One Corvette had some problem,
reportedly a transmission, that put him in the pits for a while, so
he ended up out of contention. The other Corvette won the class.
One Aston Martin (car number 007!) lost its hood at speed, making one
of the more dramatic video clips from the race. They got a new hood
on it, though, and got it back in the race quickly enough for it to
finish in 3rd place. The other Aston Martin (009) finished second.
The Saleens were last. To talk about the speed of these cars: the
Aston Martins are beautiful and they sound beautiful, but when all is
said and done they are consistently about a second a lap slower than
the Corvettes. The Saleens simply are not competitive, something I
don’t understand since on paper they certainly LOOK like they should
whup a**. It seems as though their 7-liter Ford aluminum block
engines don’t have the pop that the Corvette’s 7-liter aluminum block
engines have. One guy suggested that Mr. Saleen mainly has
experience with super- and turbocharging Mustangs (and Saleens, for
that matter) and lacks expertise with naturally aspirated engines.
Still, you’d think with the money being spent to field a couple of
cars year after year they’d find some way to get that car competitive.

Oh, well, enough.

– Kirbert

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