Mishimoto intake prototype

Fresh Air for the Fiesta! ST Performance Intake R&D, Part 4: Airbox Design and Fabrication

We’re getting closer to dyno testing! Our intake piping and turbo inlet hose are now complete. A well-designed airbox is the last portion of our intake design before we begin performance testing. The airbox will provide a shield for the filter to reduce the impact of engine bay heat. It also allows us to create a volume for cold air to enter from the stock duct, routing directly to our filter.

The airbox design was pretty extensive for this project, so this is a long post. Sit back, crack open your favorite beverage, and read on!

Airbox Fabrication

We started this process with cardboard templates. These templates helped us quickly adjust and modify the shape and bends until we had a design that provided for appropriate clearance. The space between the battery and air duct is quite slender, so the design will need to be precise.

Ford Fiesta ST intake airbox cardboard template
Ford Fiesta ST intake airbox cardboard template

Below is a look at what we have to work with regarding the stock duct. As you can see, the duct routes downward before entering the box.

Ford Fiesta ST intake airbox cardboard template
Ford Fiesta ST intake airbox cardboard template

We then fit this portion of our airbox with the air filter in place to check clearances.

Ford Fiesta ST intake airbox cardboard template
Ford Fiesta ST intake airbox cardboard template

Once we confirmed the overall shape and the bends needed, we laid this template out on a steel sheet to create our first portion of the airbox.

Ford Fiesta ST intake airbox cardboard template
Ford Fiesta ST intake airbox cardboard template

Off to the band saw to make our cuts!

Fiesta ST parts fabrication
Fiesta ST parts fabrication

A few bends of our prototype, and we had the first portion of our box in steel.

Fiesta ST parts fabrication
Fiesta ST parts fabrication

Check out this piece in place on the vehicle!

Fiesta ST parts fabrication
Fiesta ST parts fabrication
Fiesta ST parts fabrication
Fiesta ST parts fabrication

Now we tackle the next portion of the box, the side with pipe entry. This will not only shroud the filter, but it will also provide for support and placement of the pipe.

We designed this portion a bit differently. After dimensions were pulled from the existing three sides, we drew a model of the projected piece in Solidworks and then printed a template. This template was then glued to a steel plate and cut into shape.

Ford Fiesta ST intake airbox fabrication
Ford Fiesta ST intake airbox fabrication
Ford Fiesta ST intake airbox fabrication
Ford Fiesta ST intake airbox fabrication

The opposite side was then constructed in a similar manner and tacked into place.

Ford Fiesta ST intake airbox fabrication
Ford Fiesta ST intake airbox fabrication

One interesting feature not yet discussed is the mounting points for the airbox, specifically those on the base. The stock airbox uses two posts that slide into grommets on the chassis. We wanted to use these mounting points with our design, so we designed an identical post. For accuracy, we designed these components in Solidworks and printed them using our 3D printer. Once complete, the posts were adhered to the base of the box in the proper location. Check it out!

Fiesta ST parts fabrication
Fiesta ST parts fabrication

The final piece needed was an airbox lid that would fully encompass the filter and isolate it from the warm engine bay. We spent a good amount of time designing this piece, as we wanted it to follow the contour of the body and engine compartment. Check out the beginnings of this piece!

Fiesta ST parts fabrication
Fiesta ST parts fabrication
Fiesta ST parts fabrication
Fiesta ST parts fabrication

This will be converted to steel as well!

Fiesta ST parts fabrication
Fiesta ST parts fabrication

But wait … there’s more! We wanted to add a bit of uniqueness to the design of our airbox. Our engineers noted an area near the fender well that should be exposed to additional airflow. Taking a cue from our oil cooler bracket design for the Focus ST, we used the hexagonal grille pattern to open up the driver’s side of the airbox.

Check out our 3D-printed prototype piece.

Airbox fabrication
Airbox fabrication

This piece was then installed on the side of the airbox,

Airbox fabrication
Airbox fabrication

… and the airbox was installed on the vehicle.

Airbox fabrication
Airbox fabrication

We still need to evaluate the grid addition to decide if it will be included in the final design. We want to ensure that this component does not have a negative impact on intake temperatures or airflow entering through the front duct.

Final Testing Prototype

Below is a look at our first prototype fully prepared for dyno testing!

Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype
Mishimoto intake prototype

Coming Up!

We are prepared to test both the sound and power produced by our prototype intake! Check back next time for a compilation from our pulls, as well as a summary of our results.

Thanks for reading!

-John

Leave a Reply

Your email address will not be published. Required fields are marked *