- My model of MX-5 is: __1.5 ND
- I’m based near: Oxford
- I’m looking for technical help or recommendations on: __Wether it’s worth replacing a standard air filter with a K &N at 6 times the price.
No.
On any car it’s only worth fitting an air filter that can flow more air if the rest is set up to take advantage of it. Like with bbr turbo setups the only time they mandate switching to k&n panels is when upgrading from stage 1 (260hp) to stage 2 (300hp) and this is probably because only at that level does it become a restriction 
.
Thank you Mad Malc and Dean for your advice. I think I will keep the extra cash in my pocket for now
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using K&N filters is an investment.
so if you look at it from an engine performance perspective it wont give you much benefit (as in hp increase) however reducing the filter resistivity - as in reducing pumping losses will increase efficiency and therefore will somewhat increase fuel efficiency (edit only at WOT as its pointed out so I’m pretty sure you don’t floor the car on public roads so I’m retracting the cost savings comment). would those savings translate to the additional cost of the filter - well it depends on how many miles you do per year. Also if you invest in K&N you have to invest in the cleaning detergent and you have to apply the red oil on the filter. Because the filter is less restrictive the car has nicer induction noise over the stock filter.
so to answer you question does it worth the extra cost… well it depends on what kind of person you are (petrolhead or not) and whether you consider a K&N filter too expensive. I have one, I use K&N in my cars regardless. However it won’t magically give you +5 hp but two stripes on the side of the car will (+6 hp for each stipe I’m told)
K&N were designed or cars with carbs. Modern cars have MAF sensors and injectors, the oil from the K&N will over time kill the MAF. All for no real benefit. Save your money for a beer
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As stated by E, it has been reported on here many times. Why invest in a possible future problem for zero gains, absolutely pointless.
appreciate this from the manufacturer but this is their response on the subject
https://www.knfilters.co.uk/maf/massair.htm#:~:text=We%20are%20aware%20of%20the,it%20is%20not%20even%20possible.
personally, I have had maf sensors die on normal unmodified cars. so IMHO do it if you want, don’t do it if you don’t want. its not like a maf sensor is prohibitly expensive
This is a standard ND1.5 owner that is asking for advice on his situation. I repeat NO.
I concur with this, 100%.
I know I am going to be even less popular for this but…the first job I got after graduating was designing aftermarket air filters for the “Max Power” target audience…as well as some motorsport applications. We were a direct competitor to K&N and were later bought out by them.
A replacement panel filter or cone filter in the above scenario will yield two tenths of F.A. in terms of performance and fuel economy. WIll make a better noise but, that is about it, I am afraid. If you were running a heavily boosted car (circa 1 bar of boost or more) then an aftermarket kit might be worth going for.
I don’t want to antagonise our resident expert on all things mechanical and aerodynamic but the intake pumping losses in a gasoline engine are a result of the throttle only being partially open during “normal” part-load driving. That is how we fundamentally control the amount of torque/power a gasoline engine can produce - by limiting the amount of air going into the cylinders. An aftermarket filter will not reduce these intake pumping losses because they are caused by the throttling effect of the errrr…throttle.
For the love of all that is holy, I beseech our resident expert not to trawl the internet and post a link to some shyte in an attempt to disprove what I have written. Sometimes, we just have to accept that some people may know a bit more about certain subjects than we do.
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no I totally agree with you. the only benefit of reducing pumping loss is at wot and you pay the money mostly for enhanced noise perception…
yet is a choice and the whole point of all of us that contributed was to make the person that asked the question understand what you get with your money.
Thank you all for your input. I have learnt a lot. As i have only had my standard ND for six weeks and absolutely love driving it I will not be spending the extra on a K&N just to enhance the noise slightly. It sounds like I would be better off saving up for a better exhaust system in the future.
I’ve actually found it the past that installing free flowing air filters on na cars without any tuning or additional supporting upgrades actually reduced ■■■ dyno low end throttle response and low down torque at the expense of a measly high rpm hp gain.
Good discussion, each to their own on items like these I believe.
I stuck a K&N induction kit on my 911 back in 2008, …
Roooaaaarrrrr ! Big smile on my face, sounded like something biblical was going on in the back seats😁
My childrens opinion however ? who were sat in the back over the engine with hands on ears … well that’s another story.
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Expensive solution to a non existent problem. Waste of money.
Not forgetting that its job is to filter intake air. Is it even an upgrade?
Probably more like a marketing triumph. That being said, I’ve a ramair foam cone on my car, it reveals much engine sound including the turbo spool, which makes for an entertaining drive.
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Put it on your Christmas list, and get the best of both worlds.
That’s what I did 
Now there’s a thought 
I put a K&N on a Honda Civic VTi over 20 years ago. I don’t know if it made it any faster but it certainly sounded faster!
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And that’s the bit the detractors don’t like. Why pay £thousands for extra performance you’ll never use when you can get a placebo effect just as pleasant on the ear for under 60 quid!
It means you don’t have to drive any faster, using less fuel and helping with the climate crisis. Win, win.
Perhaps the government could give us subsidies to buy one. We could have a K and N logo on our number plate like the green flash, zero road tax boys have. Salary sacrifice schemes, 100% capital allowance, the scope for creative bungs is endless.
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