It comes with a 74mm, same as most of the V8's. The upgrade path on the E55 is to go to a 82mm. It is, at best, an incremental improvement, and fraught with tuning issues. If you were squeezing everything else out of the M112K setup, then maybe this would be a good way forward, but tbh, I am debating on going back to the 74mm on my M113K, due to the tuning issues (research the E55 Hiccup issue).