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Unfortunately, this is not a properly-designed exhaust system. The general concensus is that the stock exhaust system
on the XJ-S is very restrictive, and the cats are a key part of that restriction. Simplest fix: take off the downpipes and
cats and bash all the innards out of them and reinstall.
Of course this will reduce the restrictions considerably, but for the optimal flow it’d be nice to have smooth pipes
instead. One possibility is to replace the US-spec downpipes with the European versions that have no catalytic
honeycombs inside. Unfortunately, they don’t have oxygen sensor ports either, and it’d be nice to maintain those.
However, oxygen sensor ports are commonly available from places like Jeg’s (page 714) or Summit (page 717) and can
be welded into the downpipes.
If you must face the emissions inspector, neither of those options will be acceptable. There are others that might be,
however. First, you could consider fitting some aftermarket catalytic convertors, preferably something broad and flat to
fit under the car and less restrictive than the originals. Or, you could consider retrofitting the later OEM cats to the
early car! According to John Napoli: “I happened to be at my local Jag dealer as someone was taking delivery of a new
pair of V12 head pipes. I noticed that these pipes did not have the corrugated metal inserts in each of the four down
tubes. These inserts are ostensibly part of the catalyst system, and are present on many V12s (including my ’82 XJ-S
H.E.). Anybody who has seen head pipes with these inserts in place would reasonably conclude that they add a lot of
restriction to the exhaust. The replacement pipes I saw today have a different shape to the cats -- more streamlined and
seemingly smaller than the cylindrical cats on the head pipes with the inserts. The parts man said that both types of
pipes are available (with the inserts and without), both are fully certified smog-wise, and that the design without the
inserts is considered a better performer because of the reduced back pressure. The downstream cats are required with
both designs. I did not inquire as to price, but it seems that anyone replacing their cats should consider these
replacements, as the Jag V12 rewards you for anything that helps it breathe better.”
EXHAUST PIPE TIPS: The XJ series Jaguars have a unique style of tip on the exhaust system, a sort of S-shaped
extension that places the outlets right out on the corners of the car. This is not a mere styling feature; these tips were
supposedly designed to correct a problem with exhaust fumes recirculating back into the car. The shape puts the outlets
out into the airstream coming around the car rather than into the dead air space behind the car. If you wish to replace
these extensions with some generic replacement tips, be prepared for fume problems when driving.
Of course, the aerodynamics are significantly different between the various XJ models and all of them have the S-
shaped tips. While the fume problem may be the case with some of them, it’s not likely to be the case with all of them.
Some people claim to have no problems, while others complain bitterly of the odors. Pay your own money, take your
own chances.
You might not really want to replace them anyway. The generic pipe tips available locally are usually cheap chrome-
plated steel, and the chrome comes off quickly and the steel underneath rusts away to nothing. The stock Jaguar tips
are made of stainless steel, so there is no plating to flake off. No matter how dirty they get, they can always be made to
look new again with a little work with some Comet cleanser.
J. C. Whitney offers stainless steel exhaust pipe tips, basically a 9” long straight piece of stainless steel pipe cut off
either straight or at an angle at the end and held in place with two setscrews. The ones to fit “1-5/8" to 1-7/8" OD pipe”
will fit the stock XJ-S muffler nicely; catalog number 12xx0949U for the straight cut end, 12xx0952Y for the angle cut
tip. Note that the outlets on the mufflers are turned down slightly, so these tips will not sit horizontally but will angle
downward a bit.
TAIL PIPES: Ernie Laprairie reports: “Just had two dual-tip Pacesetter resonators installed instead of the bulky Jag
style. Looks great and still quiet, only about 8 inches long plus chrome double tips on each side.”
ADDING A CROSSOVER PIPE: One typical performance enhancement to dual exhaust systems is to add a crossover
pipe: a connection between the two exhaust streams to permit each exhaust pulse to escape through both systems. This
idea has been used with dramatic results on V8’s, and many cars come with them from the factory.