Hello,

I am looking for some information regarding upgrading the lower half of my air box to the ST250 or RS lower air box with the duel (Top & Bottom) air entrances (Picture 1)

I have a 2014 Focus 1.0 Zetec S with the single (Top) air entrance (Picture 2)

Is this a straight swap?

Thanks

I just changed to the RS lid on my 1.6 Ecoboost, added an open end k&n filter and removed the snorkel. Well happy with the result.
Some people put the whole box in and run a cold air feed from the lower grille to the hole at the bottom of the box

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And a silicone hose for good measure.

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There are different opinions about this subject.

In my opinion a Focus ST/RS air filter housing does not bring much on a 1.0 ECOboost. It will definetely not improve any performance. The stock air filter housing of the 1.0 ECOboost is sufficient to provide the engine with more than enough air. In my opinion a replacement performance air filter is the best investment.

Many people who upgrade to the RS air filter housing only use the top part of the housing. Initially I also wanted to install the top part of the RS air filter housing because of the visual aspect. However after doing some research I decided not to install it. Among several specialists there are different opinions about the advantages of the semi-open RS air filter housing. Dreamscience for example have inserts to close the semi-open RS air filter housing to improve performance.