Royal Enfield Himalayan DNA Air Filter Inlet Bell

Owners of the wonderful Royal Enfield Himalayan 411cc adventure motorcycle often fit DNA (washable) air filters to their bikes.  

One of the options from DNA Filters is a plain steel plate that holds the filter in place.  In terms of ‘clean’ airflow paths into the filter - whilst it's an improvement on the original equipment, I thought I'd go one step further and create an inlet bell that simply sits atop the DNA plate to create better airflow paths into the filter.  

Inlet pressure losses to the air filter will be significantly reduced with this addition.  That being said, it probably won't make much difference in real-world performance - but since you already own a Himalayan, you obviously don't care about white-knuckle-jet-fighter performance from your steed.  But when one is an engineer, one is an engineer (for life), and one likes things done ‘right’.

I printed mine from PETG because of the potential higher temperatures in the area - but, to be honest - PLA would probably suffice.  It doesn't really get THAT hot at the air intake.  The part itself doesn't carry much (any?) load (it's only smoothing out air), so you don't need to go overboard with perimeters and infill etc.  Just use defaults in your slicer I reckon.  I've had mine in for about 3,000km so far, including some pretty tough adventure riding, and it's as good as the day I printed it.

Update 5th March 2025

I was a bit bored yesterday and was fooling around with onshape.  I added an updated version of the Inlet Bell (3mf and stl files).  Same basic shape - just some extra ‘fillet’ material between the mounting tabs and the semi-torus shapes.  I printed off another copy in ASA to see how it would print - and it was great (see final picture).  I used three perimeters and 20% Adaptive Cubic as infill.  I also printed the top 2mm (from 14.2 to 16.2mm) at 0.1mm layer height rather than my standard 0.2mm for a smoother finish to the top of the torus.