See my current thread "Typical MPG for a Boxster" under "Performance and Technical Chat".
The strange part of it all... I conducted the upgrade to satisfy by thirst for more HP and ultimately ended up with a "win win" situation!
Since the upgrade in November 2012, increase in performance (NO CEL) has truly been remarkable. My stock 2003 2.7L pulls extremely hard to red-line, improved throttle response & Porsche note enhanced.
Next on my list of modifications for my STOCK 03 2.7L will be to increase the size of the stock 'T' shaped plenum, TB (68mm to 74mm), air tube from the MAF, which will further UNCORK this engine.
Trust me... where I live 91 Octane fuel can average over $4.65 per gallon (soon to be $5.00), so any improvement in engine performance & efficiency is a huge plus in my book.
Typical mileage: 20 to 23 City 35 to 37 HWY (results from 3 months of monitoring via Porsche's on board computer).
Comments Welcomed!