1995 454 Mag genV to "525SC" or "HP420"

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08-07-2006, 11:57 PM

#11

FASTERDAMITT

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Re: 1995 454 Mag genV to "525SC" or "HP420"

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Originally Posted by RazorsEdge

What compression did you have to run on the engine? How about the cam? 525SC Heads? I thought the heads were the same as the 454mag.

Compression was stock whatever that is. I did use Cometic head gaskets. Cam was a hydrolic roller I think 224-230@50 510 lift. The heads that came on my 454 was the peanut port heads for some reason. The ones I bought where retangular port. What are yours?
Tom

08-08-2006, 01:14 AM

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JBmarine

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Re: 1995 454 Mag genV to "525SC" or "HP420"

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Originally Posted by Pat McPherson

Building a 420HP from your 454mag would be the easiest and least expensive upgrade. The 420HP had a Crane flat hydraulic cam and Crane gold roller rockers. I believe it had a 750CFM Holley on top of a single plane intake. The recommended max rpm for the 420 was 5200rpm.
If you want to build a marine 454 that will make power past 5500rpm, I believe you should go with a full roller cam set-up. A lot of people suggest the Crane 731 or 741. Being that you have a Gen V block, you will need the "retrofit" cam and lifters with a thrust button on the timing chain cover.
The roller cam and lifters will cost a bit more, but is the way to go when building a 5500-5600 rpm 500HP engine. The Merc HP500 502 cube had a 800cfm carb so I don't believe that you will need more than that.
Which ever route you take, the stock heads should be at least bowl ported and the exhaust ports being worked some won't hurt .

Basically correct...the 454Mag and HP420 shared a "dual-plane" intake. It was the HP450 that had the "single-plane" intake. In fact, the HP450 was the same- cam, valvetrain, and induction- set-up as an HP500 (carb) but instead using a 454 block. If you pick-up a MerCruiser High Performance srvice manual (that covers the HP420/HP450/HP465/HP500/HP525SC), it gives the cam specs, carb specs, a manifold set-up.

08-08-2006, 01:48 PM

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TeamSaris

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Re: 1995 454 Mag genV to "525SC" or "HP420"

Just remember that all GM blocks get real week at about 750 hp.

08-09-2006, 11:29 AM

#14

Pat McPherson

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Re: 1995 454 Mag genV to "525SC" or "HP420"

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Originally Posted by fast fun 2

Just remember that all GM blocks get real week at about 750 hp.

Yes, I agree the stock/production blocks can't handle more than 750HP, but what about Chevy Bowtie and Race blocks you can buy though Chevy High Performance???
Whos blocks does Merc use for the 850 and 1075???

Now, I don't think Razor is going to bolt in more than 500-600 anyway. Or is He???