Jagmaster, I'm not sure about the cold air intake you installed on your XJ, but many of the "cold air intakes" that I've seen are nothing more than a cone filter in the engine bay. On my XK8 the air is sucked in from under the front right fender. That air is going to be much colder than the air directly behind the radiator in in the engine compartment.

I'm not saying that your cold air intake doesn't improve performance, I don't know what yours looks like. I'm just saying that the cone filters in the engine bay that are sold as "cold air intakes" are actually sucking in hot engine bay air.

Here's an example of a "cold air intake" that I just found by googling. This thing is virtually worthless. It would work much better if it had a shroud around it and pipe going down into the wheel well.

 

I can attest to your comment. K&N filters ran RUIN on my XJR. Leave the paper filters that Jaguar designed the car with on there.

My god are Jaguar super sensitive.

 

What happened kind of problems did the K&N cause?

 

Temp sensors measure temperature, not wind-chill


Exactly. And the ECU's task is to deal with it. It is designed to deliver "acceptable" performance over a defined range of environmental conditions (temp, baro press, throttle settings, et al) I think guys living in the Rockies don't have a modern equivalent or "re-jetting the carb" for improved performance at high altitudes. So even if your air filter could/did change the temperature of the incoming air, the sensors measure what they see and report it to the EcU and whatever delta is involved is still present when it gets to the throttle-body. Likewise the other measured variables. The one wild-card with K&N is the oil. If you over-oil and coat the MAF sensor(s) then yes, problems may ensue.

Jagmaster was making a lot of sense along these lines.


"engineer-chosen" Maybe_oughtta read a few months' worth of Dilbert (easier/cheaper and far less stressful than spending a few years in the engineering mgmt ranks of the auto industry.) At the risk of the equivalent of telling you Santa Clause is a myth....the engineers will write a specification such that your "engineer-chosen" filter will be required to flow a minimum amount of air "clean" at a particular pressure-drop (fixed temp/humidity/baro) and it will need to demonstrate a max. pressure drop when uniformly loaded with "x" g/cm^2 of specified dust and it will need to demonstrate "y"% effectiveness at trapping particles greater than or equal in size to "z" microns in dia. There will be some environmental, vibration, and durability tests in qualification. You (or the project engineer, or, more accurately, the PURCHASING agent for the company that employs the engineer..the OEM) would be hard-pressed in most cases to find a filter that could NOT be qualified. The actual filter delivered on your new car is then "chosen" by the purchasing dept. based on the absolute cheapest price they can squeeze out of a host of suppliers with the lowest being the winner. Even if the chosen one does fail a particular bit of the test they will lean on engineering to change the spec while simultaneously putting pressure on the would-be supplier to fix the problem and offer at the same low price. Engineers are far from immune from pressure to trim costs in an industry with razor-thin margins and they have weibul data supporting the ability that their engines can make it to 36k mi (60k, 100k, pick your warranty) "unfiltered" given "normal" environmental conditions. Just so you know...their intention is to avoid "warranty cost problems" not to design an indestructible engine that will never die.

Since the OEM only buys one filter/car (two for XFR and select others) and beyond that it is the operator's cost and responsibility, you get paper. They are the cheapest, one-time solution. You would see far more variety in the types of filters chosen by the OEM's if it were something they were responsible for replacing/maintaining. Over the life of the car, washable, reuseable filters are clearly the more economic solution: K&N for 3.0L S-type? $40. Paper from Jag Dealer? $20 Rock Auto? $3.50 - $15. Increased "Moan" under WOT with K&N? Priceless. So depending where you would buy your paper, the break-even point financially is 2-5 filter changes for that model. Others may be different, but I have an eclectic mix of veh. and they all fit that range.

Just as Maybe_XJ prefers the engineer-chosen filters supplied by the dealership, because he is focused on the designed-in control system balance, I prefer washable filters for the economic advantage. Previous posters indicated they had removed K&N's due to loss of low-end torque. Wow! I'm thinking my butt-cheeks have a serious lack of sensitivity! Like Jagmaster observed, the only thing I can "feel" a performance impact before/after is the diesel Excursion* with a cold-air intake. Sorry, no 0-60 times from the track to prove it. ALL reusable filters I've used have made a noticeable change in the intake noise under WOT, however...so maybe they "sound stronger!"

In the very end, I think XJRGuy said it best in observing we should all enjoy these fine machines irrespective of how we choose to filter the air they suck in the front, or the rationale for the choice.
___________________________________--
*Didn't acquire for performance, rather a cheaper solution to mount filter and battery than OEM when rebuilding from a front-end impact.

Deja Dilbert Vu: When you experience at work what you read in Dilbert within the last month....

 

I built my "cold" air intake, what I did was I just swapped the air filter box with a huge cone shaped dry AEM filter, I know it sounds stupid but I did measure the air temp using a very sensitive thermometer and the filter gets somehow cold air, I'm not saying its ice cold, but not warm either.

 

If you stand outside naked when it's say.... 35F, you will "feel" it's cold. If you hop on a motorcycle naked and go 60mph, you will freeze your a$$ off. The K&N - because of the increase in air flow - WILL INFLUENCE the air temp sensor too, in cold or warm weather. Not just the MAF readings.

I'm done with this discussion - we're all entitled to our opinions and mine is, don't waste money with aftermarket overly-hyped-marketing-engineered products. Jeez might as well buy internet infomercial kits that will make you wealthy in 2 weeks LMAO .

 

Sorry... wind chill may have an effect on the way you "feel", but wind doesn't increase the density of the air. The intake air temperature sensor measure the actual temperature of the air. It doesn't measure the wind chill. The temperature affects the density, and that's what the ECU needs to know. Colder air is denser, therefore it contains more oxygen which means it can burn more fuel. If the IAT sensor sent the ECU the wind chill rather than the actual temperature, then the ECU would tell the injectors to inject more fuel and the mixture would be too rich, which would cause gas mileage to decrease.

The K&N does not influence the intake air temperature sensor. If the air flowing past the sensor is 34 degrees, moving the air faster isn't going to make the sensor think it's 30 degrees. If so, then you could freeze water by blowing 34 degree air past it. If you can figure out a way to do that, then you'll be a rich man because it violates several laws of physics.

 

I think you are mixing the workings of the MAF and the Temp sensor. The Temp sensor sits outside the tube where the airflow sensor is residing, and does not have an internal heat source where wind-chill would have an effect. It is a standard temp sensor.

To make it simple: you have an outside temp sensor which you can monitor on your dashboard, now if you would drive faster, does it get colder outside?

The MAF however actually does react on the wind-chill.

The wire will be heated at a constant rate, and the more air flow (wind-chill), the more it will be cooled, and the more current has to be send thru the wire. The MAF will send out a voltage proportionally to the current it has to put in the wire. Here is a picture:

 

Anyone ever notice an increase in performance in a XJ40 as a result of using a K&N air filter?

 

I guess fast moving air conducts hot/cold away from an object faster than stagnant air, but at the same time, the effect is probably so minuscule for such a small sensor. It's not like the temp sensor is a 18 pound turkey...

 

Rubbish....I have run my STR without an air filter for half a day waiting for the K&N to dry with no impact on the MAF sensor (or perfornance for that matter). The problems with K&N filters and MAF sensors relate the the oil that is applied to the filter post-cleaning. When applied too heavily (or not allowed to dry a bit) the oil can deposit on the MAF throwing codes. Some vehicles are obviously more sensitive than others however.

 

I have installed K&N air filters in every car I have ever owned. Not for any other reason than longer service intervals. In my experience they have all been identical in size and fitting to what they are replacing so the difference between it and the OEM filter is small enough that it's highly unlikely to cause an issues and since I've done 10's of thousands of miles on those vehicles and in most cases seen some improvement in either response or fuel economy as well as the reduce filter changes and no issue with the engine getting hot or change in idle, i think it's fair to say that the K&N is worth it.

HOWEVER. The jag K+N air filter that i got for my 1998 XJ8 is significantly different in depth and fitment to the Jag original. It's much shallower and requires a gasket at the top of the air box for sealing.

So it's pretty clear that the air flow will be quite a bit different than when using the stock filter. I was a bit suspicious of it due to the significant difference but figured it was better for the time being than the filthy old one i had in there - my local jaguar specialist advised me to take it out ASAP as he has personally seen lots of problems with them and the AJ series V8's found in the Jags and Land Rovers.

Just my 2 cents for what it's worth.

 

Ask yourself if you have a problem. By the information on this survey you have a 50/50 chance on an xj. I have the K&N in both my cars and to date both run just fine. I should note that both have well over 20,000mi on the filters with no repercussions.

 

As for the "wind chill" effect; it's NOT that... think about an air cooled motorcycle engine, it cannot run at 5,ooo rpm for an hour stationary without melting but, can drive 100,000 miles at speed. Thats because of air flow at speed is transfering the heat from the engine away from it... thats how the MAFS works. Think about it! It measures the heat exchanged as air flows through it.
I've used K&N's for years and they work well and DO FLOW MORE AIR than a paper filter. If the eng./air-flow does not require more air, it won't make more power but IF the filter IS a restricion for that eng. set-up then a K&N WILL make more powere as long as the Air /fuel ratio remains correct... thats what the sensors in our F.I cars do... compesate for different condions I.E temps. Air density, altitude , ect.
I vote "YES" for the K&N's!

 

Put in K&N on 2011 XJ L over a year ago. Average gas milage since then is 18.4 (never rest since install). I don't know if this is an improvement or not. NO other problems with low end or engine in general. Anyway, so far so good....

 

Guys,
There is no "straight standard answer" like "good" or "bad" when it comes to that subject. It very much depends on so many factors.
First I completely agree with Jag tech and others that even minor modifications may throw off the right balance the ECU is mapped to provide. Power gain (if any) would be minimal and so not worth the risk or project.
Having that said, there are times and cars where a K&N filter WITH the adjusted intake makes perfect sense. I.e. in my (long retired) Porsche Boxster S.
It worked great, added power, colder air and good sound.
BUT, it was not perfect UNTIL I had the ECU re-mapped. (Chip tuning).
So you see, all has to play together to get the desired results.

In the Porsche the K&N setup alone added only 7hp (dyno), once the ECU was remapped I got it to about +18hp which lead to new headers and exhaust to get it to +28 hp.
In other words, the K&N added 7, the ECU about 11hp and the exhaust about another 10hp to get the +28hp total.
But you get the point, neither of those mods would have accomplished great results as a standalone. Afterall , what does a perfect flow exhaust system help if you can't get perfect flow through the intake. And vice versa.
In other words, if you go the K&N route, be prepared to keep moding along quiet a bit through intake, charger pressure, MAP and ECU mapping all the way to the exhaust system. Otherwise I don't see the benefit, only down sides.
Had to get my 2 cents in