"Performance" Air Filter Fitment Questions

[Stand-in]

So I suspect that it really doesn't matter and I would be better off just porting the rest of the intake system (which I will do for fuel mpgs alone) but i want to hear that NA gasp you get with a performance air filter. More to the point I have an early style US e21 which means that it takes are filter 13721262600, and K&N makes air filters for 13721271254. Thusly I have no idea if it would fit, does anyone have experience with this? I could just swap over to late style kjet but that would be more trouble than its worth. I could also stick a cone filter at the end of the air box where the "Suction Tube" goes, but then it would not look stockish, and I would have to find a plug for the bottom of the airbox as there is a water sipe down there along with chocking the sides with the edge of an old filter.

While we are on the subject matter, what does that "suction tube" even do at the end of the day? All I can suppose is that it introduces excess pumping loss, and only slightly drops intake temperatures as it still sucks from right next to the radiator.

[Jeroen]

Apparently size or shape is different between early and late air filters, if these would be interchangeable many manufacturers would have switched to a combined version. But what are you trying to achieve? I tried a K&N inlay filter on my 323i and did not notice any difference at all, not in sound and not in performance. As these 'sports' filters are known to be worse at filtering small dust/sand particles, I threw it out again.

I don't think you will gain any performance from a filter alone, with a more open structure like with a cone shape model you may have some more intake noise but it will never come close to open filters on a set of Weber carbs.

The stock intake tube works good enough at driving speeds as it is picking up slightly cooler air on the side of the rad, never felt like changing that unless you are really going for huge performance gains, in these cases people usually sacrifice a high beam unit.

[Stand-in]

Hmm, ok well I was mainly looking for a easy first step, I am going to be going one by one through my intake and porting each individual component while I save up money for an exhaust. For instance my intake boot has those ridges that allow for flex, however I believe I can leave said flex with a rubber cement compound filling it, and would gain laminar flow from the AFM to the intake runner. Said intake runners could use a clean and polish inside, I'm forgetting the name for it but I think there is a process with a medium called extrusion porting that I would have to send it out for, anyways that would be another part I buy spare as I am looking to keep my originals intact. I may also see into 3dprinting intake parts, as that is a low cost method and manufacturers have moved to plastics, reducing intake temps and weight. But I would have to find a suitable medium as to avoid melting and cracking under the repeated heat cycles.

This has of course the trade off of more maintenance, but I like to mess around with engines and the constant tweaking is a hobby for me. Regarding the dust and sand, I don't live near the coast nor am I in a dusty environment, but there are a couple months during the summer when the farmers are harvesting or the forest fires are burning that I would need to swap back over (thanks united states forestry policy!). Anyways the air filters are also infinitely reusable in theory so I suppose there is money to be saved there. I suppose as a final note I should mention that I am looking to produce an m10 engine that makes around 220 hp, and I am going to be building everything else first as to make way for it and prevent bottlenecks. Hopefully with some of David Vizards knowledge I might be able to achieve it NA. But anyways, its more going to be a passion project than anything.

[Jeroen]

Nice plans indeed, and by then you better design a new housing to fit an open cone on.

[Stand-in]

Nice plans indeed, and by then you better design a new housing to fit an open cone on.

This