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Jaguar XJ-S Cold Air Intakes

Jaguar XJ-S

Cold Air Intake Photographs

Somewhere along the line, Jaguar forgot that engines are happier breathing cool outdoor air than hot engine compartment air.  This page presents several ideas for remedies to that design hack.  There are lots of pictures here so it will take a while to fully load, but with any luck at all you'll get the text first so you can be reading while the pictures load.

Kirby Palm provided cold air to the intakes with some sections of 3" exhaust pipe, some generic intake hose, some cutting and some JB Weld.  Apologies for the appearance of some of the pix; almost all the items shown are black, and left alone the photos look pretty but indiscernable.  The gamma setting on many of these pix has been raised, which makes them look awful but you can clearly see the details.

The first step is to cut out the restrictive intake trumpets to make big holes in the air filter housing covers and fit them with a short section of pipe to serve as a connection point for the intake hose.  Palm cut the short sections of pipe at an angle because it makes for such a nifty installation on the inside.  After applying JB Weld and letting it dry, some satin black paint makes it look nice:

Note that the alternative to that nifty angled pipe end is to cut it nearly flush with the front surface of the housing -- the pipe cannot protrude very far into the housing without interfering with the filter element.

Of course, some people will prefer to weld or braze this assembly.

Since the air temperature sensor for the EFI system is in the left side trumpet, it must be relocated back into the housing cover proper.  This is easily done by drilling a hole and installing it with a washer and nut; there's no need for a fancy boss as on the trumpet.  Make sure to choose the location carefully so that the tip of the sensor will not contact the filter media.

This change alone will make a significant improvement in performance, since it will allow freer airflow into the engine.  Since the purpose of those trumpets that were sawn off was to contain intake noise within the air filter housing, this change will also allow a sonorous roar to come out when the car is floored.  Some like the sound, others may not; Jaguar obviously considered it unbecoming in a luxury automobile.  Owners wishing to make up their own mind before doing anything irreversible can simply remove the air filter covers, tie the filters in place with some wire, fit the air temp sender to the end of the harness and leave it hanging, and take the car for a test drive.  Note: driving the car without air filters is not recommended.  Ever.

Yet more improvement -- in fuel economy as well as performance -- can be attained by getting cooler air into these intakes.  By providing suitable ducting coming from somewhere up front, the roar is also minimized.

In Palm's installation, the cold air is routed into the engine from the headlight compartments; there is an existing rectangular opening just behind the upper radiator grille on each side that will permit air into the headlight compartment, but an unseen panel within the compartment must have an opening cut in it to permit the air to flow through to the back end where the ducting will be connected.  Several people who have tackled this modification have agreed that cutting the hole in that unseen panel is the most difficult part of the task; once the headlights are removed the panel is right there where you can see it, it's mild steel, there's no need for neatness since it doesn't show, but the angle of the panel is somehow arranged so that almost no power tools will fit in there.

On Palm's '83, the back end of the headlight housings had holes cut and sections of 3" pipe fitted using JB Weld, similar to the installations on the air filter housing covers.  On the left side, a couple of relays under a plastic cover had to be relocated.

Here's the left side, ready for flex duct:

And the right side:

If you look carefully, you will notice some Gano radiator hose filters, a GM CS130 alternator where the air pump used to be, and an electric radiator fan.

Once the sections of exhaust pipe are in place, the only remaining task is installing a section of flexible duct.  Such ductwork is available in auto parts stores for exactly this task, since many cars use such cold air intake systems from the factory.  Just pick a suitable size and length.  Obviously, it would help to check the available sizes of flex duct before selecting the pipe used to make the pieces installed in the headlight compartments and the air filter housings.

Here's the left side of Palm's car, as completed:

You can see the relocated air temp sensor.

Here's the right side:

Palm's car has the four round headlight system, and all four headlights are really shallow so there's lots of room behind them -- so much, in fact, that Palm reinstalled the aforementioned relays in this area.  It's not known how the Euro style one-piece headlights or the later US polycarbonate oval headlights will affect such a cold air intake installation.

Al Askevold made a very similar installation to Palm's, but his car was a '90 convertible -- meaning it has ABS brakes, which means that the air filter housings are shifted forward compared to earlier cars.  Hence, the idea is the same, but the cold air hoses are a bit shorter:

Peyton Gill did a very similar modification to his '86, except that instead of using exhaust pipe he used gray plastic electrical conduit fittings.  They are a little smaller than the 3" stuff used on Palm's car -- about 2-1/2" OD, probably 2" ID -- but still plenty large enough for this job, and perhaps twice the area of the OEM air intake.

One of the benefits of using conduit fittings is that there is a sort of offset connector available, and Gill used it to make a really nice connection at the back end of the headlight compartment.

Chris Carley went a different direction with the intake mods on his '91 -- outboard:  "Pure Kirbert but out through the inner fender just forward of the wheel arch into the behind the headlights airbox. Only one hole to drill."

That electric fan doesn't look original.

Greg Meboe wanted a cold air intake on his car, but the XJ12 requires routing the hoses differently.  Rather than routing through the headlight housings, Meboe routed to the top center area above the radiator.  Here's a pic of his engine compartment:

Scott Horner went a different route -- literally!  One of his intakes is visible in this pic:

And here's the neat plumbing in the engine compartment:

Uhhhh, the intake system isn't the only thing non-original on Horner's car.  Note the six double-ended ignition coils!

Tom Bennett took a different tack on his XJ-S:  "I have made a 4-1/2" x 1" slot  which tapers into 3" round pipe scoop for each side using a heat gun and 3" plastic pipe and a bit of MDF as a former."  These photos were taken during work; he plans to add flex hose.

"Made in Qatar"?  Yes, that's where Bennett hails from.  One might conclude that a cool air intake would be helpful in his area of the world!

Looks like Tom has been having fun with his injector harness, too!

John Goodman points out that while the XJ-S may be sucking hot engine compartment air, the benefits of cooler air were not lost on the designers of the XJR-S.  The picture below is of the intake on one side of Goodman's car; this same picture appears on the XJR-S Engine page, but here the gamma has been adjusted higher to make the configuration easier to discern.

Note that that is not the standard air filter housing and trumpet; Goodman says, "The air filter trumpet is shorter and bigger diameter than the standard H.E."

Interesting idea; not physically connected, so the engine can bounce around on its mounts.  But it's still apparent that most of the air entering the intake will be cool air coming through that pipe rather than warm air from the surroundings -- at least while the car is moving at any speed.  Goodman reports that later XJR-S's had flex hoses connecting up this intake, as shown in this picture (with somebody pointing out the dual resistor packs on the XJR-S):

Goodman notes that it is possible to order the XJR-S parts and install them on a basic XJ-S from Jaguar, although since they are JaguarSport items they are not likely to come cheap.  For more info, visit the XJR-S site -- which includes a listing of part numbers unique to the XJR-S.

Finally, apparently the last few years the XJ-S was in production it came with a cold air intake system, as seen in this pic of a '94 seen on EBay:

The hood on the XJ-S was revised with a center bulge for the 6-cylinder engine, and in the early 90's that bulged hood was applied to V12 models as well.  It looks like Jaguar took advantage of the raised bulge to provide this cold air intake system for the V12.  Unfortunately, such a system could not be applied to earlier XJ-S's without replacing the hood as well.

Anthony DiPace owns a '94 with this intake system, and spent some time taking temperature measurements at various places inside the engine compartment while driving.  "After a 30-min drive in the Orlando FL area I recorded a temperature of 150 degrees under the bonnet."  Fahrenheit, folks, don't panic -- that's about 66ºC.  He got readings even higher, but his instrument maxed out at 158.  He then took readings right in front of those intakes, on top of the upper radiator rail, to find out how much cooler the air was there than in the engine compartment.  "The results were only 5 degrees cooler throughout the operation."

This is most disappointing, and may indicate that even these later cars may need some modification to get intake air at outdoor temperature into the engine.  Such a mod may be as simple as building a small box to extend the intake forward beyond the front of the radiator and A/C condenser.

Summation: One way or another, getting cool air to the engine is highly recommended for all Jaguar V12 owners.  It's effective, cheap and easy to do, and there are no downsides at all.

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