The airbox has an intake pipe that seems to go behind the bumper before it routes into the air box/filter, but has anyone had the bumper off and can tell me where the actual entry point is?
Is it somewhere that gets a decent intake of cool air, is there any scope to relocate it so it’s immediately behind the grille?
It’s in a good position which is why all the aftermarket cool air intakes [bar the skuzzle] make no difference to the power of the car. It sit above the bumper bar and gets nice cool air.
You could have one behind the grille but the turbulance in the air at that point will probably play havoc and confuse your MAF sensor
Great stuff!
Still, I can’t see how it would get a stream of nice cool air with it being tucked away behind there?
There’s nothing around it to heat up the air so the air is as cool as when it comes through the grill. The important bit is that it gets still air rather than messy air. A bit like when you have the roof down, it’s nice and easy to breath in the cabin out of the full windblast, stick your head over the windscreen/out the window and it becomes less so [obviously in this analogy the car has to be moving 
]
That makes sense…
I have put my windows down and head out before… Got batted by a passing insect and hit in the face at 60+ mph 
Couldn’t help laughing at that one, as an ex motorcyclist who used to wear an open face lid sometimes ,I know how much fun it is to be hit by bugs at speed , especially when they hit the lens of your glasses , and you can only see out of one eye 
I used to be into my bikes too!
My favourite insect related experience was riding down a dual carriageway squid (shorts, t-shirt, trainers only, unsafe I know but meh)…
Something that was able to sting me hit my chest at motorway speeds and not only was the impact painful, the little B****** decided to sting me too… About 1cm to the right of my left nipple… So after that I had 3 nipples. It really, really hurt!!
Made sure I dressed properly after that!
…I was riding past a lake many years ago (on a Suzuki GT250) and a dragonfly went into the side of my open face lid and jammed itself by my ear, and I could feel it buzzing , how I didn’t crash the bike I’ll never know , I did the emegency stop ,jumped of , yanked the lid off and threw it on the grass verge, and the bloody thing was still alive and flew off 
If you put it right behind the grille opening there’s always the chance of drowning your engine in the bow wave of an approaching lorry ploughing through standing water - and if it’s a foot of the ground, every chance of doing that yourself.
If you’re racing maybe every horse power counts, and that’s probably about as much as you could hope for.
In normal motoring, even if you are a speed fiend, you won’t detect it. I realised this recently when somebody (here I think) reminded me that a naturally aspirated car will lose about 3% of its power for every 1000 feet of altitude. This implies a 20-25% power drop on some of the higher alpine passes. I didn’t notice that, so I won’t be bothering with an induction kit.
The NC air intake is very well engineered, even to the air-flow flare on the entrance to reduce turbulence in the duct and maximise air speed and therefore also maximise air volume passing through. It is also as high as possible to avoid being splash-drowned while still having unrestricted flow.
The photo shown is of a later one with a little Helmholtz resonator box tacked on the outside of the bend going into the air filter cavity; this neat little bit of tuning enhances the flow performance over a wider rev range. The duct length is also significant.
Anyone who has dabbled in loudspeaker design or air-conditioning acoustics will recognise the reasons for these features.
I bought my third edition copy of Martin Colloms’ High Performance Loudspeakers in 1985 through work, but any serious designers would find it best to go for the latest (and best and most expensive but good value) seventh edition
RichardFX. What photo?
Your excellent photo above… 
You mean to tell me I have a later version airbox? My car is an nc1
The change is on 2008-2009 drawings. It is not on the 2006-2007 drawings.
I’m not sure of when the change was made.
Hmm, I edited a picture, to show the inlet flare (on both) and resonator (on later ones), but cannot seem to post it right now, even after logging in again.
Reboot PC and FF and its working.
A quick snap taken through the bonnet latch aperture just now with the borecam shows my 2008 NC has one too. The yellow line is light leaking in from the garage along the edge of the headlight assembly
The volume of the resonator is one tuning factor, the length and diameter of the port linking it to the duct are others. It’s a bit like with some exhaust systems where there is a blind box tacked onto the pipe to smooth out the flow, same equations to work out significant frequencies and overall response.
Interesting thread, learning stuff here, so if my 2006 NC doesn’t have a Helmholtz resonator would fitting an air intake with one be more beneficial than fitting the likes of a K&N or Pipercross filter to improve air flow performance?
Thanks for the info. They must have introduced it earlier [or someone retro fitted mine] as my car is an early 06 [registered in March]
My guess is that the later version is an improvement. Madza would not have added it for no reason. Maybe it was done soon after launch and the manuals took a while to catch up.
In general, a quieter inlet system across the rev range means a more laminar flow in what is a pulsed environment; less energy is wasted in the heat of shock turbulence while the air fights its way into the engine through the go-stop pulses of the valves opening and closing. By careful tuning the resonator can store some of the pressure energy off-line and return it as required . But also think of a two-stroke’s highly resonant induction with narrow rev range.
This is one of the reasons for having variable length paths inside the modern inlet manifold, and for ‘tumbling’ in the right places at the right times to ramp up the local air pressure for the moments when the valves open.
However, go-faster people who like to hear the inlet roar might be disappointed, a noisy inlet is slightly less efficient! The car is effectively gasping.
The only noise I want to hear is at the throttle butterfly. My little old Ford bitsa with two-choke progressive 32DFM Weber had the most fantastic sucking noise when the bigger second choke kicked in, and the exhaust went from an inoffensive ordinary boring old family balloon’s mumble to a snarling howl - a true wolf in sheep clothing.
Some extreme examples, no duct to big long duct.
If you have a really short inlet, eg big ITBs with short stubs to the head for quick response and maximum air flow, then you can almost ignore these pulses because the air mass is so small (nice on a racing engine), it is just a pain (black art) to get the mixture right, so go for direct injection to solve the problem. But don’t forget that bit of inlet air mass helps prevent combustion products bouncing back out the inlet valves during overlap.
A really long wide inlet duct for heavy air mass/momentum pressing in all the time at steady engine power is good for efficient conventional mixture control, but at the expense of quick changes when it falls over, (think lag or waste gate etc on a turbo).
Of course this is a big and highly technical subject and my old-fashioned thoughts are far too generalised and simplistic, and probably way out of date.
My favourite engine now is the latest Skyactive because I think Mazda have actually got it very much right.
Checked this morning my 2006 has the same air intake pipe as above pics with resonator.
Found a pic online of what must be the type without resonator box, just a shorter curved plastic pipe.
https://forum.miata.net/vb/showthread.php?t=615187
You put your bra on then
