cylinder to cylinder (I believe). Mike is having to deal with the A/F ratio from bank to bank more "systemically", as he doesn't have the capacity to tune individual cylinders. Seb seems a bit stumped as well. I talked to Greg at SZ and his educated guesses were that it could be the TBs not synced (They are synced and both go to WOT at the same time), or an issue with the cams from one bank to another (ie. A significant overlap/retard/advance difference in the two banks). In your travels have you seen this kind of difference in A/F ratios with no obvious explanation? This is one of those frustrating issues that have, so far, no obvious explanation. Thanks for your imput.