I noticed some cars produce back smoke from exhaust when fitted with big injectors like ID1000 and more. For example a turbocharged Honda S2000 fitted with ID1700 CC tuned with Hondata K-pro on 98 RON fuel pump gas, was producing back smoke under boost even through the air fuel ratio was not richer than 11.5 AFR measured at downpipe.

Is it fuel atomization problem ? do we need to alter injection timing ( injector phase ) ?

Anyone ?

Could be more fuel and air being burnt at a richer ratio compared to cruise. So you see a lot more exhaust gas then usual ?

11.5 AFR (0.78 lambda) is rich enough to produce black smoke.