these are in a 33 sutphen 1983, mod 440, ser 6181089 and 6181090. valve covers say[ custom built by mercruiser performace products 500hp] theres no cubes anywhere on motors. any idea if theses are 540s or 454s???

454's 500@ the crank and 440 at the prop..Trs boat?

it could also be the 482 that merc built back then,,i believe they were rated @ 500 hp..

440 cyclone is a 454. The 460 cyclone is the 482. Everything is the same except the stroke, compression and floating piston pins. Here's some of the specs if your interested.
440 cyclone:
8.8:1 compression
Iron rec port heads
Aluminum hi rise intake
850 Holley mech sec
4 bolt mains
Forged rods, pistons and crank
aluminum roller rockers
fully polished crank
precision angle valve job
cam 288/296
lift I .549" E .558"