The Ecotech airboxes are designed to greatly reduce induction noise, they do a very good job of it too - but at the expense of throttle response and power. Removing these restrictions can increase the performance of your car - albeit only very slightly.
If you like induction noise, you will be happy to hear that this modification transforms the sound of your engine.
This article is based on doing it to my own car, which has a C18XEL. It should be the same for most Ecotech engines.
Remove the airbox from the engine bay. Removal process depends of the type of car you have but should be fairly obvious.
Open the airbox and remove the air filter. Inspect the air filter and replace if it looks dirty. At this point, have a good look at the components and try to understand how it all works.
3. Removing Restrictions.
Inside the bottom section of the airbox is some plastic tubing. This directs air into the resonance box below which greatly reduces induction noise. Remove this from the box by compressing the clips that hold it in place and pulling up. At the front of the airbox, remove any trunking that is connected to it - leaving an opening at the front. On the underside of the box is a rubber seal which seals onto the resonance box - remove this.
4. Removal of the Resonance Box.
Jack the car up so that the drivers side front wheel can be removed. Once removed, take out some of the clips and screws that hold the inner wheel arch protector in place. Pull pack the protector to enable access to the resonance box. One Torx screw holds this in place. Remove the whole assembly.
5. Removing the Airflow Pickup.
Remove the grill and drivers side headlamp. Note - to remove the headlamp you need to remove the indicator first. Once the headlamp is removed you will be able to access the screws that holds the assembly that directs air into the airbox. Undo the screws and remove this assembly.
6. Grill modifications.
If you wish, you may modify the grill by removing the blanks that stop air flow on the far left-hand side. You will need a sharp blade to do this.
7. Redirecting Air.
Additionally, you may create a cold air feed from the front of the grill to the inlet of the airbox. If you do this, be sure that the trunking you use does not obstruct the power steering pulley. Ecotech engines should not have the same issues with taking in hot air as the C20XE does due to the addition of an air temperature sensor. Even so, the cooler the intake air, the better.
Refit the airbox complete with filter, headlamp, indicator and grill. Make sure all clips and connections are refitted securely.
You should now have a pile of parts left over - including airflow pickup, rubber connection from the pickup to the airbox, airbox internals, resonance box and the rubber seal between airbox and resonance box. It is probably best to keep these parts in case you wish to put the system back to standard when selling the car.
10. Driving the car.
As soon as you start the car you will notice a deeper sound coming from the engine bay. Ecotech engines are known for having a very throaty sound to them once the intake is de-restricted. The car should feel the same except that you may feel a very small increase in power throughout the rev range - although more noticeable at mid revs.