That's just the thing. The very same clamp & v-band have been working perfectly all the way through last year until just now - & the only evidence of blow-by was on the clamp. The only changes made since the dyno run was the powerflex hangers (because I've been trying to iron out the clunking noises), which were not a perfect fit. I couldn't see any issues with the mating faces on the v-band other than the soot from the blow by. I just hope the new clamp will sort it out.