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What's in a MCM HP425

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What's in a MCM HP425

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Old 06-23-2003, 01:57 PM
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Default 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
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Old 06-23-2003, 04:29 PM
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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.
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Old 06-23-2003, 11:23 PM
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The 450 had a Hyd. roller cam also.
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Old 06-23-2003, 11:45 PM
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Stock cam specs for the 420/425

Crane #132561 hydraulic flat tappet

228/236 .530/.551 on a 114 lobe separation
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Old 06-24-2003, 04:40 AM
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Default Compression Ratio
You guys don't know what the compressions ratio is, do you?
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Old 06-24-2003, 05:01 AM
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8.8:1
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Old 06-24-2003, 06:54 AM
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Default Supercharger?
That wouldn't be too high to strap a super charger on it, would it?
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