Originally Posted by MaddMax
I love how everyone blames this initial lean condition at the on-set of boost yet no one has been able to confirm that it truely is the culprit.
It also has nothing to do with emissions. Ford manages to get their Focus ST (turbo) to run a 13:1 or less AFR at 3500rpms.
When I've logged my 2012 WRX with the Torque App, it shows an AFR at ~13.5:1 at the on-set of boost and the richening up into the 12s shorterly thereafter (~4200rpms).
The Ecoboost 2.0L is a brand new design with DI which means it can run much higher compression. The EJ25 is an old design that wasn't originally made with today's emission restrictions in mind. There is no doubt that emissions plays a role in the factory tune.