De-restricting the Airbox

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 US airbox restriction
US airbox restriction

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.

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. 

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.

Cutting out the Ferrari 308 airbox liner
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 Ferrari 308 airbox liner
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.

Ferrari 308 airbox restriction removed
Steel liner removed

On hindsight, I could maybe have just pushed the two parts above out from the neck into the main compartment and not bothered with cutting it. Either way, all the restrictions are gone from my airbox and it is now ready for paint.

Ferrari 308 airbox ready for paint
Ready for paint

Disclaimer: 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.

Leave a comment below and/or signup with your email address to never miss a future post. Share this post on social media:

2 Responses

  1. How was it possible to get some fresh air with all that mess…..
    I guess your carbs will breathe now.

Leave a Reply