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Old 10-17-2002, 09:17 AM
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Question Engine question

Can some one tell me in laymen's terms about the Mercruiser 420's? Is that a high performance 454? Is it the early version of the 502? I am not for sure...
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Old 10-17-2002, 09:31 AM
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Early performance motor option, 420 HP 454's. Think I still have detailed specs in a brochure at home someplace. e-mail me a reminder and I'll see if I can scan a copy.

I assume these are in your new boat in the other thread?

-Greg
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Old 10-17-2002, 09:32 AM
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your a lucky guy ....there great engines....merc 454's with all the good stuff stell crank good rods rectangular heads..they were the good motors before the 454 mag and they only make 365 hp in the carb vesion yours make 420!!!!!!
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Old 10-17-2002, 09:36 AM
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Makes me feel good about my purchase......
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Old 10-17-2002, 09:55 AM
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looks like they got new Holley's on the too!!!just add good exhaust and water and your ready to rock!!!!!
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Old 10-17-2002, 11:32 AM
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I think the 420s all came with cast aluminum Gil/Merc exhaust with S/S ridsers. Are you sure they're 420s?
Check the block code on the front of the engine, it should have XF or HF as the last 2 letters if it's a 420.
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Old 10-17-2002, 11:36 AM
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I was told the exhaust on the boat was changed to 4" exhaust,, I will not be able to view the boat until next Saturday morning...
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Old 10-17-2002, 11:52 AM
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We have a pair of 420's in our Formula. They have never been cracked and have about 750 hours on them. Bullet proof has been what I've been told. We ran a poker run a couple of years ago, 3 hours at WOT 70% of the time and near that the rest of the time. We would give them a break about ever 10 minutes and back off a bit. They didn't even break a sweat.

The are build 'loose' and do go through a bit of oil at WOT. Ours have the GIL performance exhaust. The valve covers should have finned ridges, the oil caps should have spring retainers and the rollers are the gold crane series. Just open up and take a look via the oil filler.

Good choice for an older motor.

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Old 10-17-2002, 12:23 PM
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The amount of information on this website is amazing,,,,
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Old 10-17-2002, 12:58 PM
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The manifolds could have rotted out and they were replaced with the cheaper iron center rise manifolds. Was it a salt water boat?
I'm not sure if the center rise are up to flowing 420hp on that engine. You may gain a couple mph by changing the exhaust. If you're negotiating a price, that could be a good bargaining point.
Wild Horses is right, you should be able to see the gold roller rockers. The intake should be a high rise with a 850 holley.
All but the very early models came with the thunderbolt IV ignition.
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