Custom BMW N42 Short Ram Air – with an OEM+ factory works motorsport vibe

The BMW N42 engine is a wonderful piece of kit

It’s a sweet high revving screamer of a four-cylinder with its roots in the legendary S14. It is a little complicated for its own good and if not looked after and well maintained it can be woefully problematic. As a result of this, it’s a little under documented and very little in terms of aftermarket options – Fine, time to start fabricating, modding and building!

The K&N 57i is a great place to start, but if like me you were a little underwhelmed when after you ordered it, to find the box content was urm a little light? The filter, bracket and a few nuts, bolt and a washer….

It’s really easy too, but again – this is what I’ve done and I’m sharing it here with you – if you’re in any doubts or not too handy then seek professional installation *follow this guide at your own risk


The problem for me was the reliance on the 57i kit needing to use the original airbox rubber intake pipe. This if you’ve got one it has a strange baffle box as a secondary acoustic muffler (or is it a turbulence reducer?) anyhow – Once you’ve removed the restrictive factory airbox it’s actually really crap as a short ram air intake boot. It’s too thin, it rattles, and that extra section I’m sure only made matters worse. Bring on in an original BMW OEM part as I wanted an OEM look, also I needed it all to fit exactly as I’d run into Lean error codes with the old intake boot as it was not really fitting too well

The original BMW OEM part also had the vacuum line attachment – but, most of all I just wanted it to have a genuine OEM+ factory works motorsport vibe


It’s a pretty straight forward piece of fabrication too, The old intake boot needs to be cannibalized though… The new OEM part needs to be modified to work exactly as pictured, because the new OEM part has a larger diameter at one end than the other

I removed the last section of the original N42 intake boot, the section that fits over the throttle body (not the MAF) after trimming it very carefully and thoroughly cleaning it all with carburetor cleaner before I made sure the fit was perfect


The section I cut off the old intake boot fit exactly both into the new OEM part – and then the MAF fitted perfectly in there as well – snug and firm!

I smeared a generous amount of high temperature silicone adhesive on both mating surfaces, and finally pushed it all neatly and firmly together – making sure to wipe away and excess adhesive. It was touch dry in about 20 minutes and I gave it all about 2 hours before assembling it all together. I’d done a good ‘dry’ run before the final adhesive, so I was confident it would all work with the existing OEM jubilee clips, MAF, vacuum line and of course the K&N 57i


The vacuum line just stuffs itself into the hole provided, the MAF cable runs underneath and I just gently placed them together loosely with a cable tie. It’s neat and tidy, nothing rubs or could get caught up, thankfully it does look and feel very OEM+


Once it was all back together, with everything firmly in place and done up right I could just feel how much better it all was. This really is an elegant solution, and most of all it really works too. Yes, I could have just got a length of silicone tubing – but I wanted an OEM+ look and the knowledge that comes with fitting off the shelf vs made to measure – gives me great confidence when I’m driving

Finally, What’s it like to drive?

Well it’s only been a couple of days – but, my initial thoughts are that it’s great, no better than that, it’s near perfect – The plus side is that initial low rev lag that often gets complained about has all but gone, the induction sound is louder by 10/15%  the throttle response is up 20% and when I hit the loud pedal I’m sure it’s got more go, this could all be from greater air efficiency?!- only a dyno run could prove that… I’m not that bothered, it’s more about how the car feels to drive that I was interested in. As an upgrade for £15 it well worth it – as a solution it’s easy – it feels better put together, faster more responsive and the smile on my face is just that bit bigger with every opportunity to open her up and hear that heavenly induction note: as she screams for air!


*Read this all the way through, and if you’re not sure then just leave it be. I will not guarantee nor can I be held responsible for either damage to your vehicle or persons resulting from you following this guide – understand this is your choice and you are responsible for your own actions


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