Yeah, one dead cylinder will turn 800 hp into 700 hp pretty quickly. Could lose even more. We had a blown 454 on the dyno once and it dropped 250 hp from pull to pull after one of the rockers pulled the stud out of the head. It dropped from 800 to 550 hp with one dead cylinder so it really didn't like having the dead cylinder. Once the head was repaired it went back to 800 hp.