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K&N filter

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kandn
5K views 15 replies 8 participants last post by  R159 
#1 ·
Hi will a K&N filter be worth the extra money as apposed to standard what benefits are there? or would it be better just to change a standard one more often thanks
 
#3 ·
that all depends on how you fit it..if you mean cone filter..

if you can get a heat shield to seperate the filter from the rest of the engine bay then there can be some small benefits, normally in throttle response and maybe a very modest increase in HP, 2-3 maybe.

if you just remove the air box and fit, then other than a noticable induction noise you may actually hurt performance due to ''heat sink'' which is basically warm/hot dirty air going into the engine rather than cold /dense clean air from ouside.

improved induction only works where the design wasn't great to start with, and in addition to a freer flowing exhaust for a noticable performance gain.

for the optimum gains...induction/exhaust/remap.

not a fan of them myself as the oiled filters can and do foul the MAF,better modding the stock airbox and intake so its more direct,and lower down.

hope this helps
 
#4 · (Edited)
Also, on cars with forced induction it will not add any power, it might give you very small improvement on turbo spool up time.
Intake systems on cars are quite complex and precisely tuned system, and any kind of modifications, unless properly designed, simulated/tested will most likely have no effect or make it worse.
Have a look at https://www.youtube.com/watch?v=gCi2yo4UqPI and https://www.youtube.com/watch?v=PAIxeQUSg-Q
 
#5 ·
The intake on our cars is however somewhat flawed....

Flaw #1 - Inside the intake box is a long snorkel in the centre section designed to reduce noise. This also reduces airflow as the entire surface area of the circular filter is not exposed and instead only around 30% of the surface area is actually able to flow air through it. It also acts like a straw and sucks up water if you are very unlucky and fall foul of Flaw #3.

Flaw #2 - The plastic pipe that feeds cold air from the area near the centre upper location of the front grill, just in front of the radiators is extremely restrictive and significantly less diameter than the 80mm MAF and pipe to the turbo. Any gains in the flow of air from changing this will be massive but heat soak issues need to be accounted for in the design.

Flaw #3 - Said pipe from above has a habit of coming loose where it connects to the base of the intake box allowing the car to ingest water when driving through no more than 6" of water causing hydro lock and costing several thousand pounds to fix the resting damage to the engine! search the forum its a known issue that has cost people a lot of money.

Aside from that a K&N filter is just inherently better at flowing air so is always an improvement over a stock paper filter as demonstrated in this old school test:

https://www.youtube.com/watch?v=aKKn38nmXtg

In terms of damaging the MAF its true but only if your a knob. The filter has to be maintained and a filter recharge kit is needed:

http://www.ebay.co.uk/itm/K-N-Recha...arts_Vehicles_CarParts_SM&hash=item43cc2ae3be

Every few thousand miles when you would normally change your OE filter you remove the K&N one, jet wash it with the cleaning solution, then re-oil it. If you put too much oil on it you mess up the MAF. If you do it properly, its fine!

I have had a K&N on mine for 3 years and its been recharged twice. I have also removed the snorkel inside the airbox (flaw #1) and ensured that Flaw #3 is avoided by getting the pipe seal perfect with plumbers silicon tape!!

In terms of next steps, I will replace the whole intake unit with a direct induction unit, most likely candidate is a Maxogen cone filter. This is due to adding a very large Front Mounted Intercooler that will mean the air feed pipe from the radiator area (Flaw #2) has to go exposing me to severe risk of Flaw #3.

I will avoid the heat soak issues by installing the cone high up in the same location as the OE intake, although this will expose me to potential hydrolock issues in 10-12" of water so that will either have to be avoided or the alternative location employed.

The alternative location is in the engine bay itself. This is a worst case scenario and would have to be accompanied by a lot of fabricated heat shielding to deflect engine heat and supported by a cold air intake pipe from wherever I can fine cold air, likely near the location of the OE air box to feed cold air up through the hole where the old intake pipe went into the engine bay.

Its a work in progress so i'll let you know how it pans out.

In answer to the OP's question, yes get a K&N. A lot of us on here have.
 
#6 ·
One of those videos show a "restricted" intake being replaced by a high flowing k&n filter and car actually producing less power - just because the intake is not tuned anymore - https://www.youtube.com/watch?v=PAIxeQUSg-Q .
Unless somebody actually tries it and has a real numbers to prove that modified k&n system produces more power/better airflow when in a car (steady air flow produced by a fan proves nothing - in real life car produces quite a lot of shock waves going through the system which then are damped by the resonators around the MAF and design of the intake) i'm going to remain very skeptical about home made modification to air intake system.

A radiused inlet (trumpet shape) will flow as much air as one that is 2x the size but without the trumpet - so simply sticking a bigger pipe might be making things worse.

Also on forced induction engines, you don't care about intake system before the turbo as much as on N/A engines, as long as it's good enough to keep manifold pressurised you will gain no extra power (there might be slight improvement in turbo lag).

On top of that K&N filters are not as good as OEM at cleaning the air Filtration Testing for Amsoil, K&N, Napa, Jackson Racing, Baldwin, and Mazda air filters on a Miata Debunking the K&N Myth - Why OEM is Better : Nissan Articles.
 
#8 ·
Unless somebody actually tries it and has a real numbers to prove that modified k&n system produces more power/better airflow when in a car (steady air flow produced by a fan proves nothing - in real life car produces quite a lot of shock waves going through the system which then are damped by the resonators around the MAF and design of the intake) i'm going to remain very skeptical about home made modification to air intake system.
An interesting point Jacek, but with no mods to the intake and the replacement of the stock filter with a free flowing one would surely, by your own logic, not alter the resonance and/or shockwave patterns nor would the overall fluid dynamics have been changed, but it "would" be able to flow more air. Given a K&N usually gets added after the cars have been increased in power from stock 210/200 to 250/260 this extra flow of air would benefit the increased airflow request from the Turbo, or perhaps not...

With regard to the point on trumpet shaped volume flows, do you have examples of the shapes etc? If you look at the design of the initial intake pipe from the radiator area to the airbox it is very narrow so as to squeeze past the rads. This, along with the entry point into the airbox itself has been modified by at least 2 forum members who have significantly tuned their cars (clogz & Coxy) Clogz did quite a lot of data logging on the subject before making the change to the first stage intake, but for the reasons you stated, kept the airbox itself.

Although I would like to keep the airbox, the intercooler that will be fitted might not make it viable to get a cold air feed to the airbox without cutting a hole in the bumper, so switching to a more direct feed system abale to scavenge air may be the only solution. If I do end up switching I do not intend to change the MAF or resonator out but instead just replace the airbox that connects to the MAF with a direct Maxogen Cone. This way I keep the shockwave absorption designed by the engineers and gain a scavenge air feed.

The resonator box has two isolated chambers, one before and one after the MAF, not interconnected so the shockwave absorption turbo side would not be effected by removing the airbox itself.
 
#10 ·
Useful info, thanks Jacek. The note about intercooler performance vs cold air source is very useful as this makes the placement inside the engine bay less of a problem should it be necessary :thumbs:
 
#11 · (Edited)
was just mulling that over...... I am assuming that this is due to the turbo raising the temp of the air under pressure to a higher level than that of ambient and/or caused by heat soak, so the actual manifold temperature is entirely down to post compression cooling, i.e the intercooler efficiency.

Is that the general principle?
 
#12 ·
Basically, two things heat up air in the turbocharger, hot turbocharger being in contact with air and more importantly adiabatic heating (it's actually the same process as used in air conditioning and fridges, compress gas in one place which heats it up, and then cool it back down, which at enough pressure will even turn it into liquid, then allow it to evaporate and expand in another place, sucking up the heat), which is related to ideal gas law which basically states that if you keep gas volume constant and compress it x2 (so instead of atmospheric 1 bar you've got 2bar) gas temperature will be increased 2x (absolute temperature in Kelvins, so you start with 293K at 20C, so gaining 10C - 3% at air intake is a lot of effort but it's not going to give you a lot, but improving intercooler efficiency by 3% is a lot easier task), but because gas after turbocharger expands, temperature rise is not as high (typically below 150-200C), then it's cooled in the intercooler and you end up with nice cold(-ish) pressurised air.

Same reason why compressed air powered tools get colder as they operate (or even freeze), and your tyre valve gets hot when pumping your tyres.
 
#14 ·
re: cold air feed vs in engine bay

if you're traveling at ~50mph, how much hotter do people think that the air in the front of the engine bay is than the air outside the car?

If the car is stationary there'd obviously be a big difference, but at 50mph it will be infinitesimal, as the air will be in the engine bay for only a fraction of a second
 
#15 ·
I have no personal frame of reference to make the assessment from so the assumption is the heat of the engine and the restriction of airflow due to baffles, shields etc would lead to a higher temp of ambient air under the bonnet at any speed. Of this is not the case then it's good to know
 
#16 ·
With the multiscan thing you can log inlet temp to see what does what for air intake not sure how much impact there will be after the air has gone through a turbo and intercooler. Might be more beneficial on a N/A motor.

I have a BMC element, it sounds nice.
 
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