because they filter better

Can you explain this bit please ?

They filter the air better than a std £5 air filter does.

I thought that was quite a simple observation.

Well, yes, but it all hinges on what you mean by better.
An air filter needs to remove dirt, cause minimum air flow restriction and have a long service interval.
Which of these do you think a foam filter does better than the paper one the manufacturers fitted ?

Without wishing to be rude, can you back this claim up with a bit of “science” like they do in the shampoo ads?
edit this was aimed at l ache

K&N are cotton and Oil so they will remove the dirt better than a std paper filter. You pointed out one of the reasons in your previous post.

Science even if it is bias

I got as far as this…

…will increase engine performance measured by horsepower and throttle response (torque)

… and gave up.
Torque is not throttle response.

I also pointed out that a paper element will clog with dirt, reducing engine performance, but still protecting the engine from dirt.
The sticky coating on a foam filter will clog, leaving the much larger bubble holes to allow the dirt to pass through.
This is acceptable on a race engine, where the filter can be washed and re oiled very race, but a bit of a chore on a road car.

Regarding the performance advantage, there’s plenty of 500bhp trucks around with paper air filters.
Typical service routine would be to blow the filter out with an air line every 6 weeks/10 000 miles and replace it every year/70 000 miles.

the key thing it boils down to in my mind is this :

if you could get a 10% increase in power, by removing a paper air filter and filter box (cost to manufacture, lets say £20) and replacing it with a K&N air filter assembly (cost to manufacture, lets say £5), I’m pretty sure Ford, Skoda et al would be doing just that.

Thing is, they don’t. Which means either

The power difference on an otherwise stock car is naff all (obviously when something is tuned up the filter can be a limiting factor)

They let crap into the engine which would lead to engine failures within the 3 year warranty period

On Grand Turismo 5, changing for a sport air filter gives you 5-10 extra bhp for only 250 credits.

K&N air filter assembly (cost to manufacture, lets say £5)

Que?

Where can you get an aftermarket (performance) filter for less than the OEM version?

Also youve got type aproval, emmisisons legislation, customer expectations, etc to contend with as a manufacturer. The most Joe Blogs has to do is get it through an MOT. If Joe Blogs wants a noisier engine, lower economy and faster acceleration he can opt to fit a £70 air filter from K&N that gives all 3.

However if the manufacturer did that Nanna Joanna Blogs, Joes Gran, wouldn’t buy the car, so no only are they spending £50 more than they need to on the filter, they also lost £15000 by not selling the car to the whole market.

p.s. oil on foam filters are just fine for filtering, plenty of motorbikes use them, both of mine had them and neither was what you’d call sporty!

not sure I agree on the worse economy – how would reducing intake drag reduce economy? if anything it should increase (marginally)

the parts prices were a guess, but I recon if you asked your local manufacturer for the cost of an air box and air filter, the price would be higher than that of a K&N – hence my guess at parts prices. Even if it cost an extra £10 to manufacture, I think the cost on a £15000 car is rather negligable.

Noise might be one thing – but even cars set up to deliberately be loud (for instance, s2000, 350z etc) don’t have ‘performance’ air filters – they’re still a panel filter with an airbox. I bet if they could get an extra 10bhp for a £20 part (bare in mind these are highly tuned > 200bhp cars anyway, so thats < 5% increase), without a significant negative impact, they would.

But its still a cost, £20 * several million cars is quite a bit.

And most people dont want to do a DIY service every 1000miles to clean the filter out. Its a comprimise, you’ve got to make a car that people want to buy, no one that needs a service each time you pop up to glentress.

However some people dont mind that kind of maintenance, and thats where foam/oil filters come in.

Go on, show me an independent dyno graph showing before and after, for an air filter. I double dare you!!!

I think I have some graphs at home in Dave Vizards guide to tuning the A-Series Engine, but I’m sure the mixture would have been adjusted, otherwise what would the point be! lol

If you’ve got one of those new fangled cars with an ECU, you’ll need to reset it when you install a new air filter. There is usually a trick to reset it, and then it will learn the correct fuel/air mixture. I know thats what my Mondy does, can stall upto 3 times before it gets it right.

I think I have some graphs at home in Dave Vizards guide to tuning the A-Series Engine, but I’m sure the mixture would have been adjusted, otherwise what would the point be! lol

If you’ve got one of those new fangled cars with an ECU, you’ll need to reset it when you install a new air filter. There is usually a trick to reset it, and then it will learn the correct fuel/air mixture. I know thats what my Mondy does, can stall upto 3 times before it gets it right

I’m not sure. The correct air-fuel mixture is the same regardless of what filter you have on a car, assuming the temperature of the air you’re getting (and the pressure) is broadly the same. The fact there is more air shouldn’t matter – a MAF meeter will pick up that there is more air going into the engine, and adjust the amount of fuel accordingly – just as if you have the throttle a little wider open or the revs a little higher up.

Similarly, on a old carb setup, the amount of fuel put into the engine is proportionate to the amount of air flowing through the carb. Increasing the airflow by removing the intake resistance would be the same as upping the revs, more air = more fuel. The only place you might end up in difficulty is WOT at max revs – the carb might not be able to dump enough fuel into the engine to keep up with the amount of air

Lets face it, if we are talking about cars and increasing performance WOT is something that will be used a lot, so tuning for WOT is something you have to do, especially with a damn mini!

The correct air-fuel mixture is the same regardless of what filter you have on a car,

Is it really? I’m not sure about that, as the pressure difference would be a completely difference if I installed say my mondy filter on my mini. I guess you learn something new everyday… I dont profess to know much about cars, just what i think i know lol
Waiting to get flamed 😆

If you have a petrol go for a induction kit like a K&N 57i as this will produce more bhp over a normal panel filter.

The rolling road I use did some basic test on these kits, if this was only thing replaced (i.e. no other engine mods) then the kits made the engines lose power, though they make the engines sound ‘sporty’.

The manufacturers spend lots of time and effort on induction, a bit of a coiled tube and a cone on the end is not what they come up with..

best thing about K&N filters and replacement elements is not the performance gain generally, but that fact that you can clean and reoil multiple times.

If you’ve got one of those new fangled cars with an ECU, you’ll need to reset it when you install a new air filter.

most moderns with wideband lambda sensor correct fuel based on a 3d map of air/fuel ratios. Generally that map is a compromise for fuel economy, power, emissions etc

you’d be better off leaving the spare wheel at home.

Lets face it, if we are talking about cars and increasing performance WOT is something that will be used a lot, so tuning for WOT is something you have to do, especially with a damn mini!

yeah – I was talking specifically about WOT at max revs. Lets say (and I doubt this is the case) your carb can only *just* pass enough fuel for max revs @ max rpm. If you put on a mythical air filter that increases airflow by 10% across the rev range, theoretically you’d have 10% more power, up until the point where you reach your old max power figure, at which point the power curve would be flat until the point where the power would be back under 90% of max power.

It’d still make the car more drivable, as you’re only at WOT at max revs for a pretty short amount of time, but it wouldn’t help with top trumps..

“yeah – I was talking specifically about WOT at max revs. Lets say (and I doubt this is the case) your carb can only *just* pass enough fuel for max revs @ max rpm.

surely you would rejet the carb ? Simply put more air and fuel = more power.

what will happen at WOT is that the afr will start to go lean and the engine will start to lose power and combustion chamber will get over hot etc…

this leads to a pinking etc and then failure of pistons, valves and spark plugs..

also you have to adjust (increase) fuel pump jet flow/duration(carbs jets on weber etc damper oil/spring for SU/ Strom) and accel enrichment map for injection for increased flows of air and due to difference in inertia of air and fuel. you you snap the throttle open the air flow changes more quickly than the fuel rate so accel enrichment is what you need to stop the mixture going lean… until normal jets/injector rate can be matched at steady state

also airfuel ratio differ depending on whether you are looking for power or economy etc.. but also engine component cooling etc.. richer helps cool exhaust valves for example

It’d still make the car more drivable, as you’re only at WOT at max revs for a pretty short amount of time, but it wouldn’t help with top trumps..

& everyone knows, its all about the top trumps and bragging about what bits you’ve got on your car down the pub or here or PH. 😆

I miss the mini 🙁 (bragging rights)

I’ve only fitted one to a bike with the manufacturers upgrade ECU chip set to race exhaust (no silencer) and performance filter. The bike came with the standard paper filter. Seemed to make a noticeable difference. Guys who have dyno’ed the same bike show performance increases, (about 10bhp for exhaust, filter and chip). This is on a bike setup to take these modifications immediately after they’re bought as they can’t pass noise regulations setup like that. 107db at 1/3rd throttle 1M from the exhaust…

In a road car? Why bother. Better off fitting an air duct to the standard intake setup to increase air pressure. I laugh at unenclosed filters.

errrrrrrrrr……….

Not sure about other designs but…….

SU carbs which were pretty much standard on everything have the butterfly on the engine manifold side, and the slider on the filter side.

So I’m guessing youd need to re-jet or at least set them 1 step richer as your removing the restriction on the wrong side of the carb.

Apply that to a modern engine……
butterfly valve = throttle body
slider = MAF sensor, ECU and injector rolled into one.

Most cars have an exhaust sensor which can compensate for rich/lean mixtures, but its not perfect, and usualy just cuts fuel supply if its too rich. And knock sensors which show when its dangerously lean.

Faster/more expensive cars have an internal rolling road, measure the torque at fluwheel/propshaft or elswhwere and convert that to a BHP, and it knows enough other data to play arround with its own settings to find the maximum power/greatest efficiency for any given throttle opening.

Just a note, look how much power cars lose between services, TG did that experiment with a renault avantime, the gains just by replacing a stock filter were huge, similarly the oil system will use a lot of power (its pumping a fair ammount of oil at upto 5 bar), a blocked oil filter can rob a lot of that power. On older cars there’s upto 8bhp gained just swaping the mechanical fan for an electric one!

I’ve only fitted one to a bike with the manufacturers upgrade ECU chip set to race exhaust (no silencer) and performance filter and straight through exhaust. The bike came with the standard paper filter. Seemed to make a noticeable difference. Guys who have dyno’ed the same bike show performance increases, (about 10bhp for exhaust, filter and chip). This is on a bike setup to take these modifications immediately after they’re bought as they can’t pass noise regulations setup like that. 107db at 1/3rd throttle 1M from the exhaust…

Yep remapping works as you can set the map for power and sod ecomony and noise… manufacturers have to map for lots of reasons inc noise and fuel economy compliance

In a road car? Why bother. Better off fitting an air duct to the standard intake setup to increase air pressure. I laugh at unenclosed filters.

Unless you are travelling VERY quick it makes sod all difference (especially a bit of builders tube and a cone filter), better to go down forced induction route (supercharger / turbo) or look at improving induction flow using exhaust effect through valve overlap etc

I have usually found the throttle is the biggest restriction , throw on a set of throttle bodies(or DCOEs in the old days) and most cars will go faster.

Apply that to a modern engine……
butterfly valve = throttle body
slider = MAF sensor, ECU and injector rolled into one.

that is not a modern 😉

Most cars have an exhaust sensor which can compensate for rich/lean mixtures, but its not perfect, and usualy just cuts fuel supply if its too rich. And knock sensors which show when its dangerously lean.

That is a narrow band lambda, old tech now… most cars now have one or two wideband sensors, these measure a wide afr either side of lambda and thus ecu can use info to target afr information in the map.

used a wide band to set the ECU (target fuel volume/rate against load/speed not afr) on my old car..while on rolling road. Very useful as you can see a wide range of afr not just narrow afr around lambda great as power comes in lower than lambda (lambda = afr of 14.7:1 (air:fuel)

the only value in a K&N or other chav filter is the little sticker you put on your bumper/window so the rest of the world knows your a gullible fool,

snake oil,
balance bands,
digital speaker cable,
all rubbish..

foam oiled filters when excessivly oiled are known to irreperably damage MAF.
too lttle oil and it dosent filter = cylinder bore pitting.

change the paper standard filter as indicated in service interval job done.

throttle blade on petrols is more of a restriction unless your at WOT hence filter is of irrelevance 99.9999% of time for road use.

with diesels fuel = torque, a tad more air without fuel will do nothing on a diesel.

diesels will generally be limited by injector flow / pump flow prior to inlet air restrictions being of any concern.

After reading thru’ this thread & having worked in engine development & calibration for 30 years my top tip is don’t believe all you read in this thread. Some of it is true, but there’s a lot of BS. Basically for your everyday road car, only a high surface area paper filter meets the required standard for pressure drop & lifetime. Lower intake pressure losses will always be good & a lot of time is spent balancing this against cost, packaging restictions & noise. The airfilter element will only be a contributer to pressure loss together with the rest of the air ducting etc. For a standard roasd car, I’d just buy the standard filter, you won’t be able to measure any benefit.

” a tad more air without fuel will do nothing on a diesel”

so add more fuel ? Oh, most modern systems will as they run MAF of some description. Infact, quite like most petrol systems .

diesels will generally be limited by injector flow / pump flow prior to inlet air restrictions being of any concern.

Diesels are limited by boost pressure, fuel flow, combustion pressure and exhaust gas temperature. That is, if you are tuning a diesel you can increase air and fuel by fitting bigger injectors and a bigger turbo for more air and fuel. However you start getting higher exhaust gas temperatures so you then need to increase the downpipe.. then you need to screw the head down extra tightly. Then you can inject water or methanol to reduce EGTs further.. that way some blokes in Canada can get 250bhp from a MkI Golf 1.9 TD that originally had like 75bhp.

nope sorry thats wrong, they are pump controlled.

you can just bolt on a turbo and injectors and a air filter and torque the head down a bit and get gains. it dont work like that.

also its proven and shown in my experience that these shitty k&n filters which are oil based **** maf sensors completly.

the oil sticks to the wire in maf sensor which inturn gives false reading about air temp and pressure and then the ecu puts more or less fuel in thus giving pre det or pinking leading to bigger problems.

I used to tell customers to unbolt them and to bolt the standard boxes back on. this is for standard cars.

tuned or tuning cars is different. because if your tuning a car you will 1st and foremost put tbs on so you would have socks or trumpet filters its you have to but you wont be soaking it in the oil they provide just a light spray but you also wont have a maf in the sense of like you will on a standard road car.

Putting all the internet talk to one side.. i had fitted a ram air induction kit to my car around 2006 with a pipercross foam filter inside it. I took times from 30-50mph ,50-80mph etc in different gears the night before fitting it. It was a chilly night and the night after was also around the same temp. The car was warmed up well over 10 miles or so and i drove it over the same route. The times were recorded 3 or 4 times each and noted. The day after not only did it feel a bit nippier it showed on average,something around 1 sec quicker on the 50-80mph stints.some of them were around 0.8 and some around 1.2secs.yes,manual stopwatch timing in a car on the steering wheel aint accurate but when its averaging around 1 sec over a 5-7 second period,thats noticeable. None of the times were slower.

The company that produce them recon you could get around 5bhp out of the 120bhp engine.The opening at the front of the kit is around 14 inches by 2 inches and draws in cold air without it circulating around the warm bay.Its straight in there.I cant argue/say anything else. It just feels better.end of!

nice cheap,fun motoring..

dig_ecosse_ram_air_in_engine_2_25_02_06 by 924185418699ff956e470b7b637e7bc5, on Flickr

The 5bhp gain that the rolling road showed on my car with the paper filter removed is indeed a tuned engine’d running on carbs with none of this computer trickery that you talk about.

I can’t say that I particularly noticed the extra 5bhp, it’s just nice knowing that the engine is producing the power that it is intended to.

I think i’ve still got the dyno graphs from pretune, with filter and without filter. I’ll stick them up tomorrow when I get home.

After reading thru’ this thread & having worked in engine development & calibration for 30 years my top tip is don’t believe all you read in this thread. Some of it is true, but there’s a lot of BS. Basically for your everyday road car, only a high surface area paper filter meets the required standard for pressure drop & lifetime. Lower intake pressure losses will always be good & a lot of time is spent balancing this against cost, packaging restictions & noise. The airfilter element will only be a contributer to pressure loss together with the rest of the air ducting etc. For a standard roasd car, I’d just buy the standard filter, you won’t be able to measure any benefit

ok so i haven’t bothered to read very post properly, but alot of it seem to be bull tbh. this is the most accurate post here.

all on the same car, i’ve tried k&n open filter and lost torque (and therefore power), drilled the airbox and kept the oem filter and gained a bit of torque over standard. i’ve now got a handmade silicone intake system that locates the filter behind the bumper opening in direct airflow and being made from one piece it maintains smooth airflow. this system does increase performance (proven), but comes at a cost, circa. £200 new, unfortunately they’re only available for a handful of cars but there are alternatives like BMC’s CDA box.

u should look at handling and braking improvements which make the car faster than any air filter…..

Whoops, left this can out and some worms seem to have got in.

I think I’ll give it a miss then thanks.

Ultimately, on an all stock car it’s very rare that the air filter is the limiting factor in performance.

Just to quash some misconceptions….

Diesels, as a species, “benefit” just as well as petrols from a low pressure drop filter. Both need re-tuning to take advantage of it as most, if not all, rely on open-loop tuning (maps) for heavy throttle use, and so all you’ll really get is leaning out of the mixture unless you mod it to suit – this can help over-fueling petrols but will always hinder diesels, or are running at part throttle where the ECU will auto-correct the AFR. But at the end of the day, it’s still a reduced intake restriction, which means lower pumping losses and higher overall efficiency, albeit small.

On carbs the fuel filter can make a big difference, on injection systems it does require tweaking.

Generally most manufacturers, on any car with more than shopping trolley ambitions, have spent a long time tuning the intake system. People generally trash this by installing cheap/badly designed universal intake systems.

Claiming “trucks make 500hp on paper filters” is pointless and comparing apples and oranges. My car makes 300+ on no filter at all and has done so for 2 years with no ill effects (compression fine, rings fine, turbo bearings and blades fine, bore not scored), it makes a little less with a paper filter. Doesn’t mean everyone should drive round filterless. The opposite is true.

There’s loads of dyno graphs that prove that a filter alone can affect power to some degree, turbocharged cars are even more affected by it as their relative intake velocity is higher and the pressure ratio across the compressor is important – lower intake-side pressure due to a naff filter really makes the turbine work harder to reach teh required pressure – often spool time can be notably reduced with little more than a straight intake with simple oil/mesh filter. But if not carefully designed, hotter in-bay air sucked in can trash the benefits.

In answer – it’s not that simple. Each car requires thought, care and time. If you don’t want to do that, it’s probably not worth your effort.

I removed the 10 litre paint tin sized airbox in my Iveco Daily campervan and replaced it with two 85ahr batteries which has given huge benefits in space saving in the back of my van. I replaced the airbox assembly with a cheap induction kit that contains a paper cone filter and ducting to the front grill (carefully chosen to avoid any anodised bling).

Its noisier in a nice throaty way, throttle response appears better, but is it actually any faster? I’m not so sure. After reading some of this thread I’m tempted to experiment with removing the batteries, duct tape the old air filter back in and see if it drags our horsebox up a local hill faster than the 45mph it currently manages. (its not too bad considering the all up weight is around 5.2 tons with 120bhp, but if it could be affecting performance on full throttle it will give me another reason to get it remapped 🙂

The purpose of the air-filter is to filter air.
That is to remove / filter-out particulate, dust, flies etc.
So does a “better” filter with cleaner air give better BHP, performance, MPG….. possibly not.
Does this “better” filter get blocked up more quickly with the extra dust, flies, muck that it filters out “better”…. possibly yes.
The other thing about K&N (for example) filters is that they can be cleaned / washed. But only with special cleaning fluid; which is not cheap and if you use other cleaning fluid you could take the pink dye out of the filter and K&N will say your warranty for the filter is invalid.
Plus to re-oil the filter needs special K&N oil; otherwise you risk damaging / affecting the Mass Air Flow MAF sensor with oil contamination.
A lot of hastle for no obvious gain.

you can just bolt on a turbo and injectors and a air filter and torque the head down a bit and get gains. it dont work like that.

You can on those engines. No ECU, no sensors. You can get another probly 10-15bhp just by adjusting the wastegate actuator.

u should look at handling and braking improvements which make the car faster than any air filter…..

Point missed!