3D Printing: Improved Inlet Trumpets

Nothing quite gets the internet clickidy-clicks like a 3D printing article! In the following post I use 3D printing to fix something that wasn’t really broken.

The OLD Design

I have never been happy with the original mountings for the inlet trumpets on the Locost. Its quite common to use silicone hose to align everything within a retro-fit throttle body system and sadly mine was no different. This design can lead to miss-alignment between the trumpets and the throttles, potential shrouding of the inlet path and variations in inlet length; cylinder to cylinder.

This is the kind of stuff that keeps me up at night and it needed to be improved.

The original setup used a nice carbon fiber backingĀ  plate to mount the airfilter too. This was as soft as a chocolate tea pot, and four aluminum trumpets were glued-in with black polyurethane sealant. It never failed, it was light and did its job okay; but it wasn’t perfect.

I wanted a new design that would allow me to interchange different length trumpets, for testing on the dyno, and ensure the trumpets would inline with the inlet tract. So I turned to CAD to see what I could conjure up…

The NEW Design

Engine tuning is highly sensitive to inlet path length (read one of the best articles in the world if you want to know more), and I wanted to ensure that this variable remained static/constant. This being the case, It was important that the aluminium inlet trumpets were held up tight to the throttle bodies and positioned concentrically.

I started by measuring the GSXR throttle bodies that currently sit on the engine and then 3D printed some prototypes. The first design to nail down was the backing plate mounts. These would make the transition from the round throttle bodied to the flat air filter backing plate and essentially hold the whole lot to the engine.

I settled on a design that pushed onto the throttle bodies and over a useful cast-in ridge. This then clamped down with a jubilee clip. As a rule of thumb, jubilee clips aren’t super sexy, but when combined with dark grey plastic parts they can look utilitarian and purposeful.

I did try a version that held on using the friction supplied by an M4 bolts. This was a terrible idea. Plastic parts are not strong in tension and it would simply bend the mount when being tightened down.

The final design looked like this.

From here I had a nice flat surface to work. I carried across the jubilee clip compression-based design over to the trumpet side, as it worked so well on the throttle body side. This also allows quick release of the trumpets for switching to different lengths.

Its hard to see in the following CAD drawing, but the whole lot is sealed together with rubber nitrile o-rings. There is an o-ring between the backing plate and the throttle body mount, and an o-ring between the throttle body mount and the throttle body itself. These are super easy to design in, reusable and reliable.

 

Then is was simply a case of printing out eight the separate parts and cutting out the backing plate. The inner prints took approximately 3hrs each to make and the outer 2hrs each.

As always, hit go and come back later. These were made is standard PLA and, as they are on the cold side of the engine, I have no qualms about it.

The whole lot was finished off with some pretty aluminium mounting bolts for the air filter.

This setup is definitely heavier than the previous, but its far more stout and should allow for some fun experimentation on the dyno.

 

 

 

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