I have a guy with a forged shortblock , TFS Race head and Custom Blower cams, blow thru maf , new injector ...

Last year I tried to tune the car, with 11.7afr in full throttle , 20deg timing , car was blowing black smoke so I told the guy cam was not dialed properly. He did return where they built the engine and cam was installed dot to dot without install a degree wheel. So they did dialed both cam with the ICL .

Today I plugged wideband on each bank, in open loop I had bank 1 at 14.7 and bank 2 15.6 , I swapped sensor , same result. I turned close loop on, bank 1 is 2-3% lean and bank 2 10% lean.

What can cause the 8% off if it s not cam still retard ?