Offshoreonly.com - What's in a MCM HP425

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duunoit

06-23-2003 01:57 PM

What's in a MCM HP425

Does anyone know what Mercury HP did to a 454 in 1992 to make it a HP425? I'm looking to try to build it a little over next winter and don't want to miss anything.

Chris

PatriYacht

06-23-2003 04:29 PM

It's the same as a 420. Square port heads, 4 bolt mains, good 7/16's rods. Crane lists the cam specs on their web site, hydraulic flat tappet. Holley 800 on a Wiend Excellerator manifold. Good reliable engine. Mercury put Gils on these for a year or so and called them 450's.

IRONMAN

06-23-2003 11:23 PM

The 450 had a Hyd. roller cam also.

Griff

06-23-2003 11:45 PM

Stock cam specs for the 420/425

Crane #132561 hydraulic flat tappet

228/236 .530/.551 on a 114 lobe separation

duunoit

06-24-2003 04:40 AM

Compression Ratio

You guys don't know what the compressions ratio is, do you?

David

06-24-2003 05:01 AM

8.8:1

duunoit

06-24-2003 06:54 AM

Supercharger?

That wouldn't be too high to strap a super charger on it, would it?

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