MerCruiser HP420

This engine did certainly look sad when it arrived to me!
After a complete rebuild and some small upgrades it both looked and performed better than before.
For those who don't know, the MerCruiser HP420 was a late 80's step in model in the MerCruiser High Performance program. Those engines were refined at different levels - the HP420 for example had a forged GM crank, GM-TRW small dome "HO" pistons, GM 7/16" dimple rods, GM Rectangular Port heads, Manley stainless steel valves with 2.25" intake/1.88" exhaust, Crane Gold roller rockers, chrome moly push rods, Crane 298°/306° @ .004" duration flat tappet cam, a modified GM Winters Hi Rise Spread Bore intake with a 1" spacer and a Holley 850 Double Pumper on top.
This particular engine was during the rebuild upgraded with slightly higher 22 cc domed pistons and a more effective cam with a little less advertised duration but more @ .050" to get a good midrange torque for cruising as well as some power where I wanted max rpm to stay.
As this is not a race engine the dyno session was smooth as expected with just some elaboration with timing. Before leaving the dyno though, ignition timing was backed down from a max 35° to a safe 33° for every day use and to give some margin for bad fuel. This netted in 460 hp @ 5400 rpm.