power come from burning fuel... fuel needs air to burn. the engine management measures the air going into the engine and then adds the appropriate fuel.. so on one hand more air = more fuel = more power..
BUT !!!!!!!! and a big but.......... unless you have the throttle wide open... you can always add more air by opening the throttle more.

once you are wide open.... there is some weakest point for airflow... whatever is the restriction ... it can be anywhere from the tail pipe to the intake before the filter.. and anything in between. valves. manifolds, throttle bodies pipework, OR potentially the air filter.

If i were an air filter guy designing the air filter I would ask how much air can this engine suck? then I would look at how much a clean filter can flow... then how much a dirty filter can flow and then i would add a safetly factor and make sure the factory filter can flow enough air to support every need of the engine even when it is dirty.

now.. K&N is reuseable,,,, and the dealer charges 50 bucks for the paper one..so if you plan to change it more than once.. the k&N makes sense from a dollar stand point.

But for power, I dont see how a K&N filter can out perform the stock filter unless it is SERIOUSLY contaminated.


B

 

Hello chaps and chapesses

Well we're back to the old chestnut of performance airfilters (but thank goodness not spiral airflow devices to improve fuel economy).

There is no doubt that in the 1980's when carburettors were king, "throwing" fuel into the system and hoping for the best, adding a K&N filter and rejetting the carbs did make a difference.

Today the game is different. On the X type we have varaible tuned intake tracts to boost low speed torque using resonance, we have mass air flow meters, air temperature sensors and electronic throttle control and, if it overtaxes the engine, knock sensors and calibration "maps" that ensure we are working to the optimum paramaters as designed. All are managed by an ECU which has more power than the computers in the Hubble telescope.

I have used K&N's on several motorcycles in the past (1970's Hondas) and want to state that I believe that they are a premium product that deserve their reputation. But in the X type they just cannot deliver; their influence is too small compared with the other aspects of the design and the control strategy.

If you want to fit K&N's, do so because of the maintenance cost savings, not for performance. If you want performance (from the air intake), focus on the honing of the airflow passages and, in extreme, elimination of the airflow restrictions (i.e the airfilter assembly).

As has been stated in previous postings, the exhaust is actually more restrictive in relative terms compared with other applications of this family of engines. It seems in the US you can delete the engine bay converters and not be touched by the officialdom; in the UK this is not so......

Now to the Diesels. These do not have throttle plates and therefore do not suffer from low speed flow restrictions that blight their Gasoline cousins. Therefore anything that removes restrictions upstream will have a bigger effect. So if K&N market a Diesel specific product, this may be worth it. Having never upgraded a Diesel motorcycle from the 1970's I wouldn't know......

Cheers, Graham

 

agreed ... but keep in mind at any time there is only ONE bottleneck to flow. I have no clue what it is.. I imagine that a SEVERELY dirty filter will eventually become the point of highest resistance. But with a clean filter there is going to be some other restriction.

No matter what you do,, the engine wont flow more air unless the restriction is removed.

opening all kinds of other areas wont do much.

 

A couple of points.

K&N's - it seems the consensus is to buy them for servicing cost reduction only.

Dirty airfilter as a restriction. This is true, but you'd be surprised about the relative performance of the different contaminants, and how much it takes to make a difference. Usually the airfilter element is designed for worse case driving which, for this "global" vehicle, would be desert sand. If you live in Arizona or other arid areas, I would pay more attantion to the build up of contamination than, say, here in Detroit.

Certainly the normal staining of the paper from mud or dust is not going to cause a problem with airflow - indeed the specification of the paper area is always over-engineered to eliminate this aspect (the overall volume of the filter box is mainly for acoustic reasons, not flow or filtration).

If the airfilter element is wet - from ingested water or crankcase breather oil - change it immediately. The wet surface holds the dust particles in place and they locally clog the filter elements and eventually get between the fibers of the paper and render it useless. This used to be an issue with older crankcase vent systems; you could see the staining of the paper near the vent entry. These days, the consumption of oil and the vent system is more closely managed and the airfilter box is usually designed so the the oil mist does not flow directly onto the filter paper.

If you see ingested water from a recent drive through a flood - thank the humble Jaguar engineer who designed the airfilter box to protect the engine from a much worse fate. There is usually a drain hole at the bottom of the box (I've not looked at the Jag design) and this is probably plugged with dirt - clean it out so that the water can drain away.

If you are ever tempted to remove part of the airfilter assembly to gain performance, remember water ingestion is a real risk you run. You'd be amazed how standing water bounces around under the hood as you drive through it (I know I've seen the videos). Also the quest to get cold air into the engine puts the air intake snorkel in the most vulnerable position - a point of easy entry at the from of the car - which of course is easy for water, not just fresh cold air. The filter box is designed to catch the water, and sometimes you see deflector plates inside the box for this purpose.

Air intake restriction point. The pressure drop across a typical air intake is roughly 10 kPa (1/10th bar) when the throttle is fully open - i.e not much. In the X type design, the use of computer controlled dual path airflow manifolds to create positive resonances at low throttle openings is a much more important design feature for everyday driving. Now - if you have the ability to play around with these resonances (i.e mess with the calibration), as well as ensuring that the flow path is as smooth as possible, then you may get an improvement worth seeing. The trade off may be a less smooth transition between low and high speed torque, which would be perceived as a dip in the power curve.

I'm not an expert on this particular design, but would guess the most restrictive point in the induction system is the engine intake valves themselves.