De-restricting the Airbox

Published by David Flett on

With the airbox off the car, I was able to remove the airflow restriction that Ferrari had saddled my car with at the factory as a US-spec carburettor car. The US airboxes have a lot of sound deadening stuffed behind a perforated steel liner in the neck of the airbox. 

Ferrari 308 airbox restriction
US airbox sound deadening

Not only does this restriction attenuate the sound of the Weber carburetors (bad), it also restricts the amount of air getting to the carburetors and therefore reduces the power (very bad) and finally it traps moisture that eventually rusts out the airbox (also bad).

From the state of my airbox, it was clear that no air was flowing through those clogged-up perforations. The steel liner is spot welded in place, so the first job is to grind off the welds with a Dremel.

Cutting Ferrari 308 airbox restriction
Grinding off the welds

With the welds gone I removed the part the steel liner in the main compartment so I could start removing the sound deadening material. Most of the sound deadening material is in this section of the airbox. Once removed, it looked like rock wool to me, but I was not taking any chances and wore a mask and gloves for protection. 

Ferrari 308 airbox sound deadening
Sound deadening material

The material removal still left 70% of the perforated liner in place and even that would still restrict the airflow so I decided to start cutting from the opposite neck end with the Dremel.  A flexible drive attachment was needed because the liner is 5 inches inside the airbox, behind the emission flap and access is limited.

Gringind Ferrari 308 welds
Cutting the liner from the neck

For jobs like these, I always use the branded Dremel cutting disks with the ‘EZ lock’ because I find they really do cut through metal quicker than the generic disks.

Cutting out the liner from Ferrari 308 airbox
Cutting out the liner

With the liner cut completely around inside the neck, the middle part can be removed easily by pushing it down away from the neck into the large compartment. Removing this also seemed to free up the final piece of liner framing the oval restriction near the flap. A few bangs with a rubber hammer and a large screwdriver were enough to dislodge the remains of that as well.

Remains of Ferrari 308 airbox liner
Steel liner removed

With the liner cut completely around inside the neck, the middle part can be removed easily by pushing it down away from the neck into the large compartment. Removing this also seemed to free up the final piece of liner framing the oval restriction near the flap. A few bangs with a rubber hammer and a large screwdriver were enough to dislodge the remains of that as well.

Ferrari 308 airbox
Ready for paint

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Disclaimer: 308restoration.com describes the restoration work I perform on my car and only my car. I am not a professional mechanic. The website content is presented for entertainment purposes only and should not be seen as any kind of advice, information, instruction or guidance for working on any other car. The opinions stated here are my own and no-one else’s.

Categories: Restoration

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