Does that thing have one of these?

https://www.ebay.com/itm/321176153744

had a 454 boat motor doing the exact same thing,it had blown the head gasket between 4 and 6 and the more gas you gave it the worse it got.i discovered upon teardown that #6 had broken rings and a lot of oil was entering the cylinder causing it to detonate,ended up doing a complete rebuild including boring&new pistons.runs like a champ now.

that,s funny chit baja chicken.

My first guess was intake valve is stuck open or exhaust valve is stuck closed. I don't hear any valve train ticking noise though so Mike could have it right.
I'd do a compression test.

Do the valve covers clear the exhaust manifolds?

its a car engine.

68 impala. I was being funny...

sounds like a valve not going up and down, or a muffler bearing going south....

OSO is serious business lately! No jokes allowed

Tks for the help everyone. Mike I hope your not right for my friends sake but get what your saying. I'm gonna start with valve covers tomorrow and hopefully we'll find a broken exhaust stud or rocker. if nothing visual we'll role engine over and check intake and exhaust valves for full lift. Hope it's not a wiped out exh lobe. Next will move onto comp test. Just pressed for time but wanna help out a friend.

Keep all posted in what we find.
Tks
jr