Jaguar XJ-S. Manual - part 9

ENGINE

H.E. VS. NON-H.E.: The H.E. (High Efficiency) engine, with 11.5:1 compression (12.5:1 outside the US) and a swirl
combustion head designed by Porsche expert Michael May, was introduced in July 1981 and indicated by the letters
“H.E.” on the back of the car in place of the former “V12” emblem. In 1986, the H.E. emblem was unceremoniously
dropped and a V12 emblem was used once again, but the H.E. combustion chamber design continued to be used in all
Jaguar V12 engines until it ceased production.

If you have an engine laying around and need to know which it is, the trick is to look at the spark plugs. The plugs on
the pre-H.E. tilt forward or rearward and are relatively easy to replace. The plugs on the H.E. tilt toward the centerline
of the engine just enough to make them a real pain to get a socket on.

ENGINE NUMBERS: The engine number is stamped on the top rear center of the block just forward of the joint with
the GM400 transmission bellhousing, but it is typically hard to find because it is covered with grime. Paul Hackbart
sends this tip: “Take your oil dipstick out and get on the passenger side of car. You can stick it through near the oil
pressure sender and scratch away until you see it. Just make certain you clean it off afterwards.”

The XK’s Unlimited catalog includes a guide of engine numbers for the XK 6-cylinder and the V12. It provides the
following info on the V12:

7S1001>

E-type Series III

3/1971-2/1975

7P1001>

XJ12 Series I

1972-73

7P4000>

XJ12 Series II

1973 (Carbs)

7P25001>

XJ12 Series II

1974-79 (EFI)

7P?>

XJ12 Series III

1979-8?

8S1001>

XJ-S

up to 1980

8S18001> XJ-S

H.E.

1981-87

For more detail on XJ-S engines, Richard Mansell sends this helpful data from “The XJ-S Collectors Guide”:

8S4551

Feb 76 Canister type oil filter introduced

8S5203

Oct 76

Revised EFI

8S6454

Modified fuel pump

8S7017

Apr 77 GM400 introduced

8S8632

Nov 77 Stronger manual trans selector shafts

8S10195 May 78 Modified air filter box to stop blowing off!!

8S11262 Oct 78

Ignition amplifier re-located

8S13094 Oct 78

Twin V groove water pump pulley introduced

8S16401 Nov 80 Digital P injection introduced*

8S17194 Nov 80 Sump plug relocated

8S18001 Jul 81

HE Introduced

Most changes after this are listed by VIN number but the following are listed too:

8S24175

Metric threaded cylinder heads

8S26992

Piston spec modified

8S27297

Inlet manifold modified to remove holes for cold start injectors

8S31737

Modified drive plate

8S41339

Spark plugs changed from B6EFS to BR7EFS

8S41344

Sump oil baffle plate changed

8S44227

Water pump bearing size increased

8S44317

Full flow oil cooling replaces relief flow

8S45527

GM400 revalved, modified sump pan

* Apparently the November 1980 introduction of Digital P is incorrect, as Ron Kelnhofer owns a Digital P car built in
June 1980. His engine number is 8S17116SB, which does not conflict with the data in the listing, so perhaps only the
date is incorrect.

5.3 vs. 6.0 LITER: The Jaguar V12, from its introduction in the E-type MkIII up to 1993, has been a 5.3 liter engine
(326 c.i.), with a bore of 90 mm and a stroke of 70 mm.

Engines are often described by the relationship of bore to stroke. When the bore equals the stroke, the engine is
described as “square”. Early gasoline engines tended to have long strokes and small bores, described as “under-
square”. Racing engines have evolved to having the bore larger than the stroke, or “over-square”. The Jaguar V12 was
designed to reestablish Jaguar’s eminence as a world-beater in the racing community (and prior to the fuel crisis of the
early 70’s), hence the considerably over-square design. It was quite successful in this regard, still winning LeMans
races in the late 80’s.

The popularity of over-square engines in racing is actually somewhat artificial. Most racing programs divide
competition into classes based on engine displacement. An over-square design provides the most power for a given
displacement, since it permits higher RPM and provides room for large valves. However, these priorities do not
translate well to street use. Over-square engines tend to be heavy for their displacement; a larger displacement engine
of comparable size and weight can be constructed with a nearly square configuration. The over-square layout also
results in larger surface areas in the combustion chamber, which absorb combustion heat and reduce fuel efficiency.
And while the design provides excellent power at high RPM, it tends to lack torque at lower RPM; since people like
their engines to be turning slowly when cruising on the freeway, an over-square engine can seem anemic under these
operating conditions.

Ford suspended production of the V12 for 1993, and reintroduced it in 1994 as a 6.0 liter (366 c.i.). More than merely
an engine enlargement, the change made the V12 much less over-square, since the change was entirely an increase in
stroke; the new engine has a 90 mm bore and a 78.5 mm stroke. This would tend to make the engine much more
suitable for street use. It remains more over-square than most engines, and hence can provide excellent performance at
high RPM, but is more tolerant of stop-and-go driving conditions and tall final drive ratios. The Michael May-designed
H.E. combustion chambers remain in use in the larger engine, while the compression ratio has been reduced to 11.0:1.

Tom Walkinshaw Racing (TWR) was offering 6.0 litre engines much earlier. According to Richard Mansell, “TWR
started making ‘sporty’ XJ-S’s in 1984. One of the options then was a 6.0 litre engine.” John Goodman reports that
TWR also made 6.2 and 6.4 litre versions, and maybe even a 6.7.

Later on the JaguarSport XJR-S also had a 6.0. Mansell: “When JaguarSport officially started producing the XJR-S in
1988 only a 5.3 litre engine was available. It was not until mid-89 that the 6.0 litre was introduced as standard. This
was then discontinued in 1993 as by then the standard XJ-S now had a 6.0 litre engine.”

Note, however, that the 1993-on updated engine has a lot of other features these earlier engines lacked, such as a
revised bolt pattern for connecting the GM400 transmission.

WHAT’S IN A REDLINE?: Some people, probably accustomed to American pushrod V8’s, feel that the 6500 RPM
redline marked on the tach is really aggessive and far too high for an engine this big for everyday use. Nothing could
be farther from the truth; this is not an American pushrod V8, it’s an OHC V12 with an unusually short stroke. Roger
Bywater, who worked in the engine development department at Jaguar when this engine was designed, provides a more
realistic understanding of just what that 6500 RPM redline is all about: “6500 r.p.m. is certainly safe and 7000 would
not be a cause for concern. In fact I know of basically standard 5.3 V12s cobbled together with second hand bits being
taken to near 8000 in race cars without suffering any problems at all. On the other hand an elderly engine does deserve
a certain amount of respect. I expect the one thing that would result is that the timing chain and tensioner would start to
show signs of distress a bit sooner if subjected to continual high r.p.m. In reality, there is not much point in revving a
standard V12 beyond 6000 because it will be running out of breath anyway and therefore won't be making much
power.

“The real problem taking these engines to 6000 and above is that the GM 400 torque converter distorts under
centrifugal loads so that the blading can make contact creating fine metallic particles which then cause accelerated wear
of the transmission. A way around this is to use a furnace braized converter which is more rigid and able to tolerate the
higher r.p.m. without distorting so much.”

END OF AN ERA: The final Jaguar V12 engine was built April 17, 1997.

HOT SHUTDOWNS: It is never a good idea to shut down an engine immediately after running it hard; it is always
better to run it at reduced power for a few minutes first to let it “cool down”. This has nothing to do with the
temperature reading of the coolant; the problem lies with parts within the engine that get much hotter at full load than at
low load, and can be subjected to high thermal stresses if the transition from high load to off is too sudden.

This problem is especially serious in the case of the Jaguar XJ-S. Several problems the car seems to have, including
vapor locks, distributor seizings, and ignition amplifier failures, may be exacerbated by hot shutdowns. The underhood
temperatures may skyrocket after a hot shutdown, and Jaguar is known to have had underhood temperature problems
during development of this car.

Whenever you are driving the car hard, always drive the car leisurely for a few minutes before shutting it off. If you are
forced to shut the engine off after running hard -- having a mechanical problem, for example -- at least open the bonnet
to allow the heat to rise out of the engine compartment, providing some convective cooling.

See page 227 for tips on improving post-shutdown cooling.

KNOCKING/PINGING/PINKING/DETONATION/WHATEVER:  Regardless of what you call that sound, it ain’t
good for an engine. A brief description of what’s going on:  When an engine is running properly, the fuel/air mixture
within the cylinder is ignited by the spark plug and the flame front grows continuously and spreads throughout the
combustion chamber until the entire charge has been burned. However, while this is going on, the piston is moving
upwards towards the head, compressing the charge and thereby heating it. In the most severe cases of knocking, the
compression causes the charge to self-ignite before the spark plug even fires. The result is that the entire charge ignites
at once, rather than the gradual ignition of the flame front moving through the charge. This “explosion” has been
likened to hitting the piston with a hammer.  It can damage the piston, connecting rods, and the bearings in both ends of
the con rods.

What usually happens is less severe, however. The spark plug fires well before the piston reaches the top of its stroke,
so the flame front has begun its travel while the compression is still in progress. Since the burning charge is expanding,
it is compressing the unburned charge into the far corners of the combustion chamber. The combined effects of the
piston rising and the flame-induced pressure causes the remaining portions of the charge to self-ignite. The actual
amount of charge exploded in this fashion can vary anywhere from a tiny portion to the entire charge, so knocking can
be either severe or barely detectable.

There are many factors that contribute to knocking. The most notorious is compression ratio; the higher the
compression ratio, the more likely it is for the charge to be detonated. Another key issue is the octane of the fuel, which
is a measure of how hot it must be before it self-ignites; the higher the octane, the hotter the mixture must get before it
will burn. And ignition timing is a factor, since lighting the mixture earlier will cause more of the charge to be burned
before the piston gets to TDC and therefore increase the peak pressure.

Other factors include the intake air temperature, the fuel temperature, and cylinder wall and head temperatures. EGR,
which puts some inert gases into the mixture, makes it harder to ignite and therefore reduces the tendency to knock.
Also, there are some minor details that can complicate the issue; sharp edges in the combustion chamber can act as
“glow plugs” and ignite the charge prematurely. Carbon deposits can increase the compression ratio, as well as provide
glowing embers to preignite the charge.

Knocking can be difficult to detect on the Jaguar V12. All those little cylinders mean that each knock is small, and all
that sound deadening built into the car keeps the driver from hearing much of anything in the engine compartment.
Basically, if you can hear it at all, you might need to be concerned. On the other hand, Mike Wilson reports: “I asked
the local Jaguar rep and he had the audacity to say that "All Marelli cars ping". He said it was even in the owners
manual! So, I came home and read mine and sure enough, there it was in black and white! It said that a small amount
of pinging was normal and if it happens on flat roads under no load, to see your dealer for further assistance.”

If something needs to be done about pinging, the usual reactions include changing to better octane fuel or retarding the
timing. On the later XJ-S with Marelli ignition, you can’t adjust the timing by just rotating the distributor, so a jumper
was provided that can be pulled to put the system onto a more retarded map when needed. Even if we try to buy good
fuel, occasionally we always seem to get a tankful of real crap, and this jumper is a handy fix to get us to the next fillup.

Joe Ziehl shares some experience: “My mechanic told me to first try a higher octane fuel because while retarding the
timing may help, the preignition might be caused by something other than spark plugs, such as carbon in cylinders or
on pistons. He also recommended that I treat the gasoline and run the car hard for a few days. This made a significant
improvement in the pinging.”

Jeff Elmore reports: “I had been getting some slight pinging under medium acceleration after the car had warmed up. I
had tried many things, including checking the timing, high octane gas, etc. Then I tried the temperature at the
thermostats. It was 213°F on one side and 203°F on the other. I just changed the thermostats and topped off the
coolant (almost half a gallon low), and the pinging is gone. The car now runs better as a result, with my guess being
that a lower CWT sensor means more fuel and power.”

Andrew Stott reports: “Autocar magazine had an XJ12 HE on long term test and in their 12,000 mile report (May 8
1982) they had quite a bit about the knocking noise and clouds of smoke at around 4,000rpm in 1st following a couple
of weeks of gentle, town driving. Apparently, the Jaguar engineers discovered this quite early on in the development of
the May heads and ran special endurance tests to highlight any problems, none were found.

“In their 36,000 mile report (April 9 1983) Autocar actually had one of the heads removed and found nothing at all
amiss, not the slightest suggestion of pinking damage, and no measurable ovality or wear in the bores. There are
pictures in the report. They also ran performance tests and found the car to be just as it was at 12,000 miles.

“Both these reports are in the Brooklands book on the XJ6 & XJ12 Series III (1979-1985), ISBN 0 946489 98X.”

The experience on the internet discussion lists indicate there is one sure-fire cure for knocking: the Italian Tune-Up.
Get the car fully warmed up, then while cruising along at about 60 mph, move the shifter into 2 and punch it. Hold the
pedal to the metal until somewhere close to redline, then let off and coast back to 60 -- and repeat. The first time or
two, the car will show its displeasure by stumbling and blowing great clouds of black smoke out the rear. After a few
such accelerations, the car will react much better to being punched, even feeling as though it is anxious to do it again,
and there will be no trace of smoke. Owners consistently report there is no longer any trace of engine knock either, and
the car runs better all around.

Obviously, an Italian Tune-Up wouldn’t be a good idea if the engine has serious mechanical faults such as fuel supply
problems, overheating problems, etc. It also wouldn’t be good to run it through a speed trap.

People think I’m makin’ this stuff up about the Italian Tune-Up. Bill de Creeft provides a quote from a British car
magazine after the HE engine came out: “...if one runs the car for not less than a working week of relatively gentle
driving, typically commuting with no longer journeys between, then, once properly warm, accelerates flat out, the
engine goes through a period between 4500 and 5000 rpm of loud detonation accompanied by pale but noticeable
exhaust smoke. You learn, after the first rather frightening occasion, to keep your foot down regardless, to accelerate
through the knocking which, together with the smoke, stops and doesn't return until after the next period of town
running. Jaguar,and Michael May, say that in gentle driving or with a lot of cold starts and short journeys combustion
deposits build up in the head and on the valves. On hard acceleration these deposits heat up and burn, causing
detonation but clearing, as they burn off into smoke. Jaguar says that in tests they conducted before the engine's launch
(in July '81) in which such deposit-induced detonation was sustained artificially for long periods of hard running,
showed no sign of piston or head damage.”

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