totally depends on the severity of the crack,if it was large and on the bottom where you couldnt see it and it was causing a pressure drop in the headpipe,that would cause a major diff in the performance,another reason why your water box would be running really hot as well,post this and your findings in the thread I linked here,just one more thing to look for when tuning a bpipe,and another great reason to test on a water hose