Pulled the heads off the Challenger because after doing a cylinder leak down and compression test I found 1 week cylinder. # 1 cyl had 80% leakage! I have 452 heads that are suppose to be hardened seats. It looks like they forgot to harden this one. The exh valve sunk into the head. All the rest were O.K. Using the porting templets then new exh seats & a valve job.