Hybrid airbox for a tenner (ish).....

75289 Views 124 Replies 42 Participants Last post by  DolbyWills
This is my first how-to guide...hope you find it useful.

Please note I won't be held responsible for any loss, damage, cuts, bruises or colourful language that may result from following my guide

Never being one to leave things alone i've been looking into modding my R53 airbox into a Dave-F esque hybrid unit. I could obviously have bought one but that wouldn't have been much fun, would it?

Anyway, I did a bit of googling and came up with a plan of attack. I whipped open my stock airbox and was horrified by the state of the existing filter.

Armed with a few measurements and a tenner I went down to my local Wickes for some bits.

First bit you need is a black plastic roundline downpipe connector (£1.49p). This was chosen as the internal diameter is exactly the same as that of your existing airbox outlet, and the external diameter is near as makes no difference to the internal dimension of the K&N filter we'll be using (more about that later though). First chop off the whole of the largest portion like this...(keep the bit you remove as you'll need this later)

You should end up with something resembling this after a light sand to remove the rough bits (notice the nice radius curve thats already within the pipe)

Next mark out a 1cm line with masking tape and cut this off too

You should, if you're careful end up with something like this...

It'll fit into the airbox like this when we're done

Next you'll need some raw material to make a plate to mount the modified pipe connector onto. I sourced this from a roundline rainwater hopper (£7.99) I chose this as there's loads of plastic, and its the same plastic as the pipe so you get a strong bond when you glue it. Oh, you'll also need some solvent cement

Make a cardboard template that fits like this, snug against the existing rib in the airbox

transfer this onto the hopper and cut out a plate

I should fit like this

cover it in masking tape

then offer it up to the airbox and mark your outlet hole

I tried to cut this with a hole saw, but the battery on my drill went flat so I ended up using a stanley knife (yep it's possible if you take your time). Trial fit your modded connector to the plate. If all is well it should be a nice snig fit. You'll notice here that i've tapered the protruding bit of connector. This give you the smoothest possible fit, and therefore flow.

Glue the two bits together with the solvent cement in this position. Don't go mad with the solvent of you'll melt it like an airfix kit. You remember the bit of connector I said to keep. Place this centrally over the bits you're gluing and put something heavy on it.......wait patiently...when the solvent has fully gone off trial fit the adaptor you've made. It should look like this

Next you'll need to seal between the back of the adapter and the airbox. I used some sticky foam. (it looks like overkill bit its very squishy) I strongly advise against using silicone.

Offer it up again, and drill the holes to bolt it in with. Top tip...if you just do one at first then bolt that up loosely the plate won't shift about when you drill the other three.
Bolt the adapter into place and check alignment

Its now you can attach your K&N. You need model RU-3190 which is the same as the one used in the Dave F Hybrid boxes

The only other mod to the airbox itself it to shave away a little bit of web which can foul the filter slightly

Now, because the original filter panel provided the seal between the top and bottom halves of the airbox you need to replace it with something. If you run a very sharp stanley knife around the seal portion of your original filter it'll come away nice and clean

You can now glue this onto the upper or lower portion of the airbox. You only need a couple of spots of glue (from a glue gun) to hold it in place while you re-install the upper section of the airbox with the filter attached

and there you have it...very stealthy

Sticker optional

Looking down the airbox outlet you can see the excellent fit and nice smooth flow you'll be getting

I'm sure there'll be much discussion about the lack of JCW/Dave F style secondary inlet through the firewall into the space below the windscreen, but to be honest, i'm not sure it's necessary unless you need massive airflow (of course I could be wrong). You already have a secondary inlet from the lower section of the original airbox which feeds from the same place. I think this with the frontal scoop should be fine. At least you don't need to go cutting more holes. With my mod, you get loads more charger whine into the cabin (sweet) and loads of popping and crackling on the overrun (also very nice). Obviously I don't have a dyno to give any figures but my car feels stronger, sounds better, and the mod is pretty much reversible (remove the adapter and filter and fit another panel)

Hope you like it....
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Might be be worth adding the cost of the KW filter too. Fair play for giving it a go.
Might be be worth adding the cost of the KW filter too. Fair play for giving it a go.
Oops! it would be helpful. The filter is available from ebay for a shade over £30 delivered. I collected mine from Revolution Motorsport in Gateshead and it was £32.
I think it has been proven with back to back JCW dyno runs with the flap open and closed that taking air from the extra opening does give a slight increase in power, not a huge amount, but when you start adding more mods the difference will be greater
More power is def' on the cards. My car is still under dealer warranty though so I didn't go the whole hog with the additional inlet (come to think of it, the sticker may have to go lol). This'll do me for the interim though, it sounds awesome..
Looks great!
Excellent job, well done! I would def consider this if I wasn't so lazy lol. Dave F for me :p
Good effort but where is the more important extra cold air feed that comes from your bulkhead?
The bonnet is designed so that it forces air down through the scuttle panel and then into the air box.

Who was it that made a nice mini scoop on their scuttle panel to feed into their airbox... That + this would be the best DIY CAI possible on a budget methinks.
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Good effort but where is the more important extra cold air feed that comes from your bulkhead?
There is already a small secondary feed from the lower section of the airbox but I take your point. As I said earlier my car is under dealer warranty so I didn't want to go chopping large visible chunks out. If I can get hold if a spare lid I may get a bit more creative.
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^ All you need is a 68mm hole saw and some drain pipe to do it anyway. I made one for mine a month or so ago, I was tempted to start selling them as they're so easy to make!
Bloody good guide by the way!!
^ All you need is a 68mm hole saw and some drain pipe to do it anyway. I made one for mine a month or so ago, I was tempted to start selling them as they're so easy to make!
Bloody good guide by the way!!
Thanks muchly! Did you just enlarge the existing secondary feed? That seems the easiest option rather than trying to cut through all the angles on the upper portion of the box. I've been toying with the idea of making a complete new lid from fibreglass to include a replacement scuttle section so you dont have to do any drilling or cutting. That'll probably end up being my winter shed project
^ Fibreglass lid like this one? - North American Motoring :: Product and Vendor Reviews - 52R - Powered by ReviewPost

I didnt have to do anything to the rear scuttle on mine, as the previous owner had a davef at one point, but sold me the car without it, however it already had the hole cut ready for the pipe to land in place.
That's pretty much what I'm aiming for, if a bit smoother in appearance. It'll take time to craft the molds but I'm up for a challenge. :laugh:
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Update ....... Nearly a month on and everything is holding together nicely. No issues of cracked glue etc
^ Good show, I checked mine the other day and that was fine also, that's been on about 7 weeks now, maybe longer, so there's something rather spivvy to be had here!
Looks good mate, I personally have the Dave.f but after reading this leaves me with a question.. Does the Dave.f have a seal? I can't remember seeing one to be fair!
I've never heard of anyone mention a seal previously either come to think of it
Hmm, might take a look later.surely defeating the object of the exercise if its pulling warm air in through the join as well.. May chop up an old filter if so!
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