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

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....