[DeTomaso] NPC indeed, marine engine problem

[Mikael]

Being around V8s for decades I thought I had seen it all, but I need help on
this on. One of my boating friends put blower kits on his twin 454+ Chevy
Marine powered boat. 78 mph at 5400, all fine, that was last year. This year he
can only get it to 72mph at 4900, and the valve covers get very hot. Reason for
that is rockers (still stamped steel) get so hot they turn blue and had to
be refinished. Many clever people have tried to help him with suggestions,
the rockers overheating has happened 4 times.

My immediate guess would be oil starvation or water in oil. But I wouldn't
know why this happened and why only this year, and why only one engine. The
oil pressure on his gauges is fine, on both engines.

I'm just throwing this problem to this forum if anybody has experienced
something similar.
Thanks

Mikael