as standard fuel mixtures run a bit rich for safety
A turbo diesel will be drawing in much more air than the displacement of the engine because of the pressure increase
In my experience performance filters do very little in increasing outright power on a standard car. They may increase throttle response but without a remap the ECU simply adjusts the fueling to keep the emissions within given parameters.
On mapped cars they do make a difference, still no where near the manufacturers claims.
On the subject of fueling to gain more power it's not just down to getting as much mixture into the cylinders as possible unless you can extract it quickly too so catalytic convertors and restrictive exhausts need to be changed to get obtain the best gains.
On more and more modern cars the limiting factor is coming down to the injectors that are only able to flow a maximum amount of fuel and no amount of smooth fast flowing pipe work and mapping can over come this.
webbers
[thread closed]
As for the argument about whether more power is nececary, only if you spend a lot of time with your foot nailed to the carpet (which you should have removed to save weight surely?) at the peak power RPM (~2/3-3/4 of the redline). If not you'd get more power by putting your foot down more and shifting gear later.
I have a K&N panel filter on my Focus And it makes the little 1.6 sound quite throaty when heavily accelerating. I would have got a full on cone filter for it but because of where the MAF sensor is I cant fit one.
BTW I am not a boy racer I just put the K&N on when doing a service because they filter better.
because they filter better
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.
I got as far as this...
...will increase engine performance measured by horsepower and throttle response (torque)
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! lolIf 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,
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 .
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