[x300] Questions about the XJR's (x300 versus x308)

X300
1

I am currently a Volvo owner/driver, but I am looking to
trade up to a ‘‘new’’ car. For a while I was thinking about
either an E39 540i 6-speed or a E38 740i sport package. My
family’s from the UK though and I’ve always been a fan of
Jaguars and so I took a look at the XJR.

Basically I’m curious about the major differences in
reliability between the X300 XJR’s with the blown AJ6 versus
the 98-00 X308’s with the v8. I’m interested in
reliability, tuneability, handling, and interior quality. I
am aware of the nikasil problem with the early v8’s and I’m
wondering if I should steer clear of v8 cars with 50-70k
miles on them. What’s the policy on replacing engines if
the problem were to pop up? Other than that I’m mostly
interested in how the electricals and suspension hold up
between the X308’s and the X300’s as well as the reliability
of the blown AJ6.

I’m also interested in how well the engines hold up to
increased boost levels (with a proper ECU reflash of course)
, as well as when they start to throw rods, etc under
increased boost. I really like the idea of having a
refined, luxurious sports sedan that’s just a blower pulley,
exhaust and reflash away from the high 400’s as far as crank
HP goes. I know thats’ the case on the AJ-V8 cars, but how
well do the AJ6 cars respond to upped boost? I’m also
curious about what the driveline can handle on the different
cars. I have heard that the X308 XJR’s use the same
transmission as the E55 AMG, but I’m not sure if that’s true
, and I am interested in what the X300’s transmission can
handle as well.

Finally I’m curious about how these cars handle, how
composed they are at high speeds, and how they might compare
to each other as well as to cars like the e39 540i and other
contemporary late 90’s to present sport sedans.

I know I’m asking alot, so thanks in advance for any info

Finally–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

2

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

I was part of the development team of the 95MY X300 XJR (X306 to
give it the specific code). The base engine is very reliable at std
performance levels. I was so impressed with the car I bought one
myself. It is a 96MY manual car with 70,000miles & full service
history. I have recently uprated it myself by fitting the
supercharger (SC) from the X308 XJR. It took me about a year to
design and have machined and fabricated all the parts, but only
about 2 weekends to fit them. I calculate it will now produce about
400bhp & 470lb.ft of torque. I am confident that the base engine
will be durable at this performance level otherwise I wouldn’t have
done it. I don’t intend to put the vehicle on a chassis dyno, as
this would be a very abusive test of a vehicle at this performance
level. Most chassis dynos can’t provide adequate vehicle cooling
for such a test. Instead I will check the in-gear accel times on
the road against the std figures to judge the performance increase.
Even more performance would be possible with an even bigger
supercharger, its just a matter of how much money you want to spend.

There is some limited scope for increasing the size of the crank
pulley to run the std SC faster but you will trade off its
durability as it is already running near its max speed. I expect
the engine would still outlast the SC itself. The max size of the
crank pulley is constrained by clearance to the anti-roll bar and
other components in the belt drive. The SC pulley is already at its
minimum size.

If you increase the performance of the std engine I would ensure
you run it on 98RON (approx 93 pump octane fuel) or higher so as
not to put excessive demands on the knock control system. If you do
this you can get away without remapping the ECU up to about 400bhp.
However you will need to measure the air fuel ratio of the exhaust
at max power to check it is still OK (11.5:1 or richer)(next task
on my own car).

It is possible to fit a smaller SC pulley on an X308 and possibly
a larger crank pulley but the same comments apply about
overspeeding the SC unit, as for X306. I can’t comment on the
durability of the base engine at elevated performance, as I have no
personal experience. The transmission in an X308 is a Mercedes
unit, not ZF as used on all the naturally aspirated X308s. I can’t
comment whether it is specifically the same as used in the AMG E55.

If you have any more detailed questions about the modifications I
made to my own car, feel free to contact me direct.–
The original message included these comments:

Basically I’m curious about the major differences in
reliability between the X300 XJR’s with the blown AJ6 versus
the 98-00 X308’s with the v8. I’m interested in

–
Andy Stodart - 1996 XJR owner and ex-Jaguar XJR engineer
Northampton, United Kingdom, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

3

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

people run any of the XJR’s on anything less than 98/93?
That seems like a real smart idea (not).

How much work did it take to fit the eaton m112 onto the
AJ6, and do you have any idea if the AJ6 internals would be
up for ~500 horsepower? What dort of driveline weaknesses
did the X300’s have, and when would you srart to run into
problems with killing transmissions, diffs, cv joints, etc.

also, aside from the transmission did the X308 have any
other driveline differences from the X300’s, and would it be
better suited for making ~500 horsepower?

As far blower upgrades, I know the X308 XJR uses the same
blower as the SVT lightning pickup truck in the US, so it
wouldn’t be too hard to find a more efficient screw-type
blower that could safely get things up to that magical 500hp
number. I’m looking to end up with a car that can hold it’s
own against the new M5, aka 11 or 12 second 1/4 miles and a
0-60 time in the 4-4.5 second range.–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

4

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

This is like a message from royalty.

‘‘I calculate it will now produce about 400bhp & 470lb.ft of
torque.’’

HOLY HELL! And a manual transmission to boot. Wow. I
understand that the XJR uses a beefy GM auto transmission,
but what sort of manual transmission is used? It, too, must
be very strong if you’re confident enough to run 400/470
through it.–
The original message included these comments:

Andy Stodart - 1996 XJR owner and ex-Jaguar XJR engineer

–
jaguarSean '97 VDP
Walpole, MA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

5

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

so the X300 XJR doesen’t use a ZF unit either?

I’m still real curious about the rear ends of these cars and
how they hold up. What style is the independant rear
suspension? Is it the same weird one using a single lower
control arm with the halfshaft as a stressed component? If
so I know that design is a real common iRS for hot rods.

I’m also still wondering about the nikasil issues on the
older V8 XJR’s–
The original message included these comments:

understand that the XJR uses a beefy GM auto transmission,

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

6

Ummm,

Try finding anything higher than 91 octane in plentiful quantities anywhere
in California.

Been running my XJR and my 420HP Mustang Cobra (also Supercharged) on 91
since I bought them.

91 octane supports up to 17lbs of boost.

XJRGUY> From: ACBarnett abarnett@wpi.edu

Reply-To: x300@jag-lovers.org
Date: Mon, 13 Mar 2006 19:05:00 +0100
To: x300@jag-lovers.org
Subject: Re: [x300] Questions about the XJR’s (x300 versus x308)

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

people run any of the XJR’s on anything less than 98/93?
That seems like a real smart idea (not).

How much work did it take to fit the eaton m112 onto the
AJ6, and do you have any idea if the AJ6 internals would be
up for ~500 horsepower? What dort of driveline weaknesses
did the X300’s have, and when would you srart to run into
problems with killing transmissions, diffs, cv joints, etc.

also, aside from the transmission did the X308 have any
other driveline differences from the X300’s, and would it be
better suited for making ~500 horsepower?

As far blower upgrades, I know the X308 XJR uses the same
blower as the SVT lightning pickup truck in the US, so it
wouldn’t be too hard to find a more efficient screw-type
blower that could safely get things up to that magical 500hp
number. I’m looking to end up with a car that can hold it’s
own against the new M5, aka 11 or 12 second 1/4 miles and a
0-60 time in the 4-4.5 second range.

ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

7

Its my understanding that the X300XJR use a GM 4L80E trans same as Chevy
Silverado and HMMWV etc.

Griff

ACBarnett wrote:> In reply to a message from jaguarSean sent Mon 13 Mar 2006:

so the X300 XJR doesen’t use a ZF unit either?

I’m still real curious about the rear ends of these cars and
how they hold up. What style is the independant rear
suspension? Is it the same weird one using a single lower
control arm with the halfshaft as a stressed component? If
so I know that design is a real common iRS for hot rods.

I’m also still wondering about the nikasil issues on the
older V8 XJR’s

The original message included these comments:

understand that the XJR uses a beefy GM auto transmission,

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

8

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

17 psi of boost from the stock XJR blower on the stock
fuel/ignition maps?

I’m in MA and I can get 93 at most any station, and 100 race
gas for strip trips and dyno runs so i’m not too worried
about that…

I’m still curious about what is known about the bottom end
strength of the AJ6 versus the AJ-V8 as well as when the
diffs/halfshafts/cvjoints cop out.–
The original message included these comments:

91 octane supports up to 17lbs of boost.

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

9

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

17 psi of boost from the stock XJR blower on the stock
fuel/ignition maps?

I’m in MA and I can get 93 at most any station, and 100 race
gas for strip trips and dyno runs so i’m not too worried
about that…

I’m still curious about what is known about the bottom end
strength of the AJ6 versus the AJ-V8 as well as when the
diffs/halfshafts/cvjoints crap out.–
The original message included these comments:

91 octane supports up to 17lbs of boost.

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

10

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

The X300 runs the AJ16 engine not the AJ6.

You might want to try the Race forum ‘next door’ if you seriously
wish to find out about destruction testing limits of transmissions
etc. People here are pretty much road car drivers as far as Jaguar
sedans are concerned, although we do have people with tuning
insights.

Being in MA and a speed freak looking to beat sports BMWs in a
large Jag luxury sedan, have you run across (or into) a guy called
Nico? :-)–
Peter Crespin 66 2+2 ‘E’
Buxton, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

11

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

thanks, I realize that alot of this site is maintinence
centered (like brickboard for volvos) and I’m asking some
bigtime performance questions. I’m not too afraid of the
engine strength as even 500 crank wouldn’t be too much
stress for the engine as far as hp/liter goes. Even the
‘‘weak rod’’ volvo motors with 9mm rods are good for about 300
crank out of a 2.3 liter engine which is alot more stress
hp/liter wise than 500 from 4 liters. The forged rods in
the AJ-v8 also sound like a real good start, especially if
the pistons are forged too (are the rods in the aJ16 forged
too?).

and no, I don’t know nico, is that his username on the board
here?–
The original message included these comments:

You might want to try the Race forum ‘next door’ if you seriously

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

12

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

The AJ6/AJ16 have very solid lower ends, 7 main bearings, etc. I
do not recall anyone having a problem.

Most people who have failures in supercharged engines tend to be
with pistons. This of course is at the entreme end.–
The original message included these comments:

I’m still curious about what is known about the bottom end
strength of the AJ6 versus the AJ-V8 as well as when the
diffs/halfshafts/cvjoints crap out.

–
uncle
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

13

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

Hi AC

Not sure I’ve ever come across a rod that wasn’t forged, unless you
count billet titanium…? Always happy to learn something new
though. Not sure a cast rod would survive much. Cast cranks, yes,
but even there I think forged is good for ultimate toughness and
grain strength.

Don’t worry about the Nico thing. I was only kidding. He’s our
resident race specialist who blows off M3s in a normally-aspirated
sedan by leaving out the spare wheel and back seat IIRC. He keeps
us all on our toes and swerves around the potholes in Boston MA so
look out if you’re in the city :-)–
Peter Crespin 66 2+2 ‘E’
Buxton, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

14

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

durrr, stupid me, I should have known better. What I meant
was is the crank forged in either the AJ16 or the AJ-v8, and
are the pistons cast or forged?

what sedan does he have, and how much are the I-6’s capable
of making when naturally aspirated. I’m also kinda curious
about what the redlines of both engine types are as well as
how much higher each one can go…–
The original message included these comments:

Not sure I’ve ever come across a rod that wasn’t forged, unless you

–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

15

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

This thread really seems to have generated some discussion. I will
try to answer the various questions aised in the whole thread.

All 6 cylinder and 8 cylinder XJRs are designed to run on 95RON
(approx 90 pump octane fuel)
I’ve probably spent about 150hrs fitting the Eaton M112 SC to my
96MY XJR.
I’ve no idea if the AJ16 or AJ26 bottom ends could handle 500bhp.
Given that the SC required to produce the required airflow would
probably take best part of another 100bhp, you are looking at

600bhp in equivalent loading on the engine. I suspect the AJ16 is
more robust as it has 7 main bearings and generous cylinder spacing
to allow wide bearings and bearings panels. But neither of these
engines were designed for such performance levels. Likewise I’ve no
idea what are the limiting components in the rest of the driveline.
What you are proposing is so far outside the design specification.

The manual transmission in my XJR is the std Getrag 290 unit used
in all 4.0L manual XJ40s and X300s, neither of which were ever sold
in the US.

Jaguar dispensed with using the driveshaft as the upper link when
XJ40 was launched. X300 uses the same suspension architecture as
XJ40.

Automatic X300 XJRs do indeed use GM Hydramaitc 4L80E
transmissions, unlike 4.0L NA X300 which uses ZF 4HP24E and the
3.2L which uses the ZF 4HP22. As well as a variety of US SUV
applications the 4L80E transmission is also used in the Bentley
Arnage which produces 850Nm of torque and 450bhp so I suspect the
transmission can cope with a significant engine performance
upgrade. However the gearbox ECU would need remapping to increase
the line pressures during shift to prevent clutch band wear.

The crank in AJ16 is forged and the pistons are cast.
Inceidentally, there is no piston oil cooling.

Maximum engine speed is limited by torsional vibration on the 4.0L
AJ16 engines, as it is a particluarly long engine. If you were to
remap the engine ECU to allow you to run above the 5750rpm max
continous running speed you would damage the TD damper. The cam
drive & valve train is good for higher speed as illustrated by the
higher revving shorter stroke 3.2L engine.

A naturally aspirated 4.0L AJ16 can produce about 270bhp without
increasing the max engine speed through conventional tuning.

Even if you overcame the torsional vibration problems the AJ16
engine will never produce particularly high specific output because
it is limited on valve area.

I think I’ve answered all your questions about AJ16 engines. I
can’t comment on AJ26 (V8s) as I never worked on them.–
Andy Stodart - 1996 XJR owner and ex-Jaguar XJR engineer
Northampton, United Kingdom, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

16

Andy,

Thanks for your contributions to this list.

I was under the impression that the pistons in the X300 XJR were forged, not
cast.

XJRGUY

From: XJRengineer andystodart@metronet.co.uk
Reply-To: x300@jag-lovers.org
Date: Tue, 14 Mar 2006 21:48:01 +0100
To: x300@jag-lovers.org
Subject: Re: [x300] Questions about the XJR’s (x300 versus x308)

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

>

The crank in AJ16 is forged and the pistons are cast.
Inceidentally, there is no piston oil cooling.

I think I’ve answered all your questions about AJ16 engines. I
can’t comment on AJ26 (V8s) as I never worked on them.

17

AC,

If you are thinking that contemporary Jags use forged crankshafts, you might
be in for a surprise. The last crankshaft used in the V12s were cast iron
… not forged. These engines produced more power and torque than their
predecessors. And guess what, the V8s also use a cast iron crankshaft.
Perhaps we need to rethink our ideas about forging being better as Jaguars
are certainly well known for their high power to displacement ratios.

Or perhaps its a testament to the ability of foundries to produce very high
quality / high strength castings in a material renown for its durability and
easy machining.

John P.

18

In reply to a message from John R. Pring sent Wed 15 Mar 2006:

yeah, it’s like how all cranks in the 40’s and early 50’s
were forged and then everyone went back to cast cranks as
the quality improved. i’m more wondering what sorts of
issues i’d have making 400-450 hp out of a AJ16 or ~500
horsepower from an AJ-v8.–
ACBarnett
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

19

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

Like the burning bush!! Fantastic first hand informational
nuggets here. Weeeee!–
The original message included these comments:

I think I’ve answered all your questions about AJ16 engines. I
can’t comment on AJ26 (V8s) as I never worked on them.

–
jaguarSean '97 VDP
Walpole, MA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

20

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

JaguarSean,

Are you becoming an XJRengineer groupie? Only joking.

It’s great to have someone of Andy’s calibre as a contributor to
our forum but, I just wished that he’d stayed with Jaguar and
worked on the XJ8 too.–
The original message included these comments:

Like the burning bush!! Fantastic first hand informational
nuggets here. Weeeee!
jaguarSean '97 VDP

–
Gary London,UK, 98 XJ8 4 www.jag-lovers.org/v.htm?1122951577
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –