If you are planning a sick build, and you are looking to make great power while maintaining responsiveness, you can't go wrong with the EFR turbos.
If you are interested in reading a little bit about the EFR Turbo's, follow this LINK to the EFR Tech Brief.
There are three EFR turbos that make great upgrades for the focus ST.
First up is the EFR 6258 - $1730.89
The EFR 6258 is the smallest and fastest spooling EFR turbocharger in the lineup. Ideal for small engines, this is an excellent turbocharger for autocross, rally, drift, road racing and street driven applications. The 62mm OD compressor has a 49.6mm inducer rated at 44lb/min max flow which is capable of supporting up to 440hp. This compressor wheel is versatile with very large map width for outstanding power potential, even at high boost. The low inertia 58mm Gamma-Ti turbine wheel is optimally matched for maximum response and fast spool with the FMW compressor wheel. EFR 6258 uses the smallest-sized EFR compressor housing, making fitment in the tightest engine bays possible. Ideal for use in single turbo applications for the 260-440hp range. Ceramic Ball Bearing only, and water cooling is recommended.
Next we have the EFR 6758 - $1730.89
The EFR 6758 is a remarkably versatile turbocharger. It is on the same B1 frame as the 6258. The compressor offers broad map width for outstanding power potential. This FMW compressor wheel measures 53.9mm inducer with 67mm OD compressor to support a 53lb/min max flow rate. Ideal for use in single turbo applications for the 300-450hp range. Ceramic Ball Bearing only, water cooling recommended.
And finally my personal favorite, the EFR 7163 - $1975
Brand new for 2014, The EFR 7163 is Borg Warner's newest addition to the EFR family. This is literally an off-the-shelf Indycar turbocharger, used by all 2014/2015 IRL teams. This FMW compressor wheel measures 57mm inducer with 71mm OD compressor to support a 60lb/min max flow rate. Ceramic Ball Bearing only, water cooling recommended. All EFR Turbos feature the Gamma-Ti Turbine wheel.