Hi Guys,
How can you tell if your 496 is 375hp or 425hp?
I have the block number(12558110) but do not know how to find out what the horse power is? Is there a web site that can tell me this? Thanks, Susan

They make both. The mag is 375 hp and the mag ho is 425 hp.

I know that make both.... The blond hair is out of the box !!!
My question is; can you tell which HP it is by the block number.
And if you can't, what numbers of the engine do you need to find out...
Thanks again,

Doesn't the Mag and the Mag HO have different engine covers and HO is on the engine cover itself?

And anohter guess, is doesn't the HO come with closed cooling system?

If you want to check it by the serial #, you have to get the Merc serial # off the back of the engine block near the starter.

BTW, if it says 496Magnum its 375hp. If it says 496Magnum HO its 425hp. It should say so right on top of the engine cover.

It may also say it on your ECU. My ECU has a sticker that says 496MAG HO followed by a bunch of numbers.

Thanks for all the help!!!!!!!!!!
Lake St Clair is almost back to water.....
Will be boating soon!!!