here are a few pics illustrating the comparative size of our Stage 1 (15 row) oil cooler
and the Stage 2 (20 row) cooler
As you can see even the Stage 1 core has more frontal surface area than the BMW OE oil cooler and significantly more core volume.
The 20 row core is a monster in comparison to the tiny OE unit.
we plan to have the complete Stage 2 oil cooler kit fitted to our 135i by this time next week.