Another turbocharger option is now residing in my basement.  I came across a classified ad for a number of 2.7T parts that included this pair of low mileage BorgWarner RS4 K04’s.  With only a little over 10,000 miles on them I could not pass up the opportunity to put some K04’s back onto my S4, or alternatively to use them as the starting point for an upgrade to a RS6 based hybrid.

For the time being I am sticking with BorgWarner K03’s to gather some additional performance data and to try and continue the Nefmoto Stage 1 Tuning thread , but my hope is to swap in the K04’s by summertime and get some numbers on them with my existing additional hardware.