When I bought my XKR it had a cone filter that pulled in a lot of hot air... and it is 108 degrees F here in Tucson right now. I bought the air filter box and intake piping from a fellow forum member. The fit is close, but I had to trim a tab off of piping to clear the intercooling system. Also, the small bolts that secure the piping to the throttle body don't line up with the bracket. It is easy to secure snugly with cable ties (zip) for now. I took it for a blast down the street prior to taking the pic and I haven't cleaned things up yet. The XKR drove great and seemed to be *slightly* more powerful, but that's just using a butt dyno. =) I'll get a feel for things over the next day.

Oh, yeah, I also had to grind a lip from the inside of the filter box inlet to get the MAF sensor to fit in properly.

 

I took the Jagger out for a spin tonight to see how it is responding to the cold air box. There is additional power after the engine has warmed. It used to be that the power would drop off quite a lot after warm up, but that has been minimized. Yes!

 

Smart move. You saved yourself some power...

 

Keep in mind that the XKR box has an extra opening at the front that is solenoid activated to let more air in when needed (at least mine has that).

Doug

 

That only came in on later 4.2 engines, I have fitted/swapped 8 and R air boxes about with no probs, dont think there are any differences ?

 

Doug,
I meant to post on that - when I took the snorkel off to clean the TB the little trap door was stuck open. The return spring is pretty feeble and enough grit had got into the plastic hinge to seize it so I had a permanent and unwanted warm air intake. Worth checking the door moves smoothly when you've got the filter box apart.

 

Hmmm... very interesting. It implies that the engineers believe that more airflow is warranted at high load. The conclusion would be that those without one might consider doing something to get more air into the box.

 

If the flap was the size of a letterbox it might do something but it isn't.
It also has a high aspect ratio and is on the atmosphere side of the filter.
I really don't see it doing much to an airflow of several hundred L/sec.

 

Well how big is it?

Bear in mind that the snorkel itself is on the atmospheric side, and is not all that big. So if one looks at it as a percentage increase and a the fact that it shortcuts the snorkel then a different perspective might be had. Consider also the the cross sectional area of the TB bore itself is less than a letter slot.

Air filters, at least good air filters, don't present much of a problem in terms of restriction. This has been proven time and again on 7+ litre carbureted motors.

 

Just been out to measure and my recollection is wrong. The flap area isn't far off the same as the wheel arch inlet area so it might have an effect. It would be difficult to say, without measuring pressure drops everywhere, if the obstruction caused by the air inlet to the filter is significant compared with the duct from filter to TB with all its odd resonators.

 

A good rule of thumb might be that if it got past the bean counters, then it must be needed

Additionally, having a bypass of the snorkel would cause more of the induction noise so beloved by SC owners.

 

I did not know that the 4.2 had the ability to open a flap in the filter box to flow more air! Does anyone have a photo of it that they can post?

I used the XK8 intake pipe since it does not have the noise reducing ports. I saw in the forum how folks have used plastic welding techniques to close those off. The XK8 pipe doesn't have them (see pic in orig. post).

 

I can't really get at it with a camera and don't want to pull off the outlet pipe + filter body top.
It is an oval flap pivoted like a butterfly valve of the same sort of shape and dimensions as the intake pipe. It is at the front of the filter box with a solenoid inside.
The filter box carries an electrical connector for it.
No pic in JTIS either, sorry.

 

When I originally bought my XKR I immediately started looking into what typical bolt-ons might be available. Ones that were readily available when I originally bought my Corvette were K&N filter (of course), lower temp thermostat, adjustable fuel pressure regulator, very easy ways of reprogramming the ECU, and gizmos to improve air intake such as throttle body airfoil and modifications to the basic inlet mechanism.

The only so-called easy bolt-on for the Jaguar was the K&N filter and that is when I noticed the secondary intake flap (as pointed out this is at least the same size as the snorkel). So I figured that air flow, at least at the box, was not going to be an issue. However what is an obvious issue is the snaking tube that runs from the box to the throttle body and then has to make a 90-degree bend downwards. It seems that an obvious area of improvement for these engines would be to have relocated the throttle body right at the front of the engine facing forward (as in the Chevy LT-1 and LS engines). Air flow from the inlet to the throttle body was a straight short shot which intuitively has to be better than the convoluted path in our engines.

Doug

 

Doug,
I'm sure you're right. It is a very complex subject but as a rough idea a sharp 90° turn approximately doubles the flow resistance of a pipe. There is one 45°, one swept 90° and a horrible 90° into the TB in the output pipe. I can't be bothered to measure pressure drops but my gut feeling is that the outlet pipe is the worst flow restricting culprit.
It is interesting, though, that the flap is a butterfly rather than a letterbox which suggests they might have been worrying about it opening passively due to depression in the filter box.

 

I will look at the intake snorkel again today. Perhaps replacing the snorkel with a larger diameter black PVC pipe will be an improvement. I'd have to cut the snorkel hole in the fender well area to match the larger pipe diameter, then match it into the air box. A 4" diameter section of pipe, approx. 8" in length, may do the trick. Hmm... that would gain the advantages of the possibility of more air intake under WOT without the need for a solenoid operated flap, AND it would be cool air. Hmm...

 

Well, it chimes with the Physician's old mantra
Primum non nocere' (first of all do no harm)
and is a solution too simple and elegant for Jaguar particularly as you're aspirating colder air than normally found under the bonnet.
You'll need to look at where the snorkel actually ends in the wheel arch in relation to the (whatever it's called) plastic wobbly thing that lines the wheel arch.

 

The pipe that goes into the fender has about the same diameter as the 75mm TB, although it is oblong. There is also no bend anymore, and the end has a bell house shape. So to be honest, not much to gain there for a stock car. If you beef it all up, then better go straight for a large cone filter under the headlight.

 

I did a quick look once to see if I could figure out where the actual entrance was that fed the snorkel that disappears into the wheel well/fender. I had expected to see some inlet behind the front grill but did not see anything. I can't believe that it is just sucking dead air from the whatever space there is in the fender?

Doug

 

Its not dead air, the fender gets filled with fresh cold air from the front bumber, its all open!