how can you find out the power rating of a 454 mag?

if it reads 454 mag and its a efi engine its most likely a 385 hp version..take the serial number iff the side of the block or on the intake and call merc.

Or post the number here, I'm sure someone can look it up for you.

365 HP if its carb'd and 385 if its EFI

Ok004424

Serial Number Range




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454 MAG. BRAVO (GEN. V) GM 454 V-8 1996-1997

0F801700 - 0K999999

Serial number OK004424, Model number 4454110KS 1997 MERCRUISER W/PS, TWO PC EX, GEN 6, 454 BRAVO, with a carburetor = 350hp.

See page 1B-4
http://www.boatfix.com/merc/Servmanl/16/16B1R2.PDF

So, does that mean it is or is not a ho engine? Forged internal rather than cast?

The is no such thing as an HO engine for a Merc 454. Its either a Magnum engine or its a regular 454/7.4. The 454magnums have all good forged internals.

The 350 hp rating is at the prop. Its rated 365hp at the crank.

Thank you.