Hello you wonder if you can use the new umbrella valve seals on a 78 305ci Chevy instead of the old small rubber ones?
Yes you can. Order them by application at your local auto parts store.
The 1980 Camaro came with 7 different engines to choose from. 2 of them were for California only, the 231ci 6cyl @ 110hp or the 305ci 8cyl @ 155hp (165hp in the Z/28). The other motors are the 229ci 6cyl @ 115hp, the debut of a 267ci 8cyl @ 120hp, a 305ci 8cyl @ 155hp, and a 350ci 8cyl (In the nonCA Z/28s) @ 190hp
Considering you're asking this in the Chevy 305 section I'm assuming you are meaning 305ci(cubic inches) instead of cc(cubic centimetres) big difference.As for your actual question it all depends what year/make/model the engine is from and what kind of shape it's in. For the exact numbers though you're going to have to run it on a dyno.