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Merc 420 roller cam upgrade

Old 01-25-2020, 01:27 AM
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Default Merc 420 roller cam upgrade

Hey guys, I am planning to rebuild my 454 mag motors to 420 ish specs, with roller rockers and larger carb, exhaust. However I would like to put a roller cam in it. Does anyone have any suggestions on what would work in this engine and what I could expect to see using the roller cam? Iím kind of learning as I go here and would also be curious of what the thoughts are for valves/ springs as well.

Thank you
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Old 01-25-2020, 01:54 AM
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What exhaust do you have??

Crane 168731 is a good choice
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Old 01-25-2020, 02:28 AM
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Originally Posted by Griff View Post
What exhaust do you have??

Crane 168731 is a good choice
x2
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Old 01-25-2020, 09:15 AM
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Not 100 percent yet on exhaust. But what I have and have been working on is the older 420 exhaust manifolds that have the 6 bolts for the riser. I am making my own riser. I have created block off plates as the base of my riser w/ 4Ē stainless pipe, and planning either stainless boxed tube or larger pipe as my shell. Manifold has water line taped into it that attaches to a hose barb in the riser. so you can say custom exhaust or just assume it is basically like the original 420!3xhauat manifolds with gil risers.
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Old 01-25-2020, 11:46 AM
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731 cam works well in Mag motors. As far as exhaust , I ran early 420 six bolt riser exhaust ( Merc switched to Gil exh on late 420's), on my race boat for one season. Switched to Stainless Marine and lost over hundred pounds on stern , 10x easier to service motors , and could actually feel the weight difference in handling. These come up for sale in pairs frequently at very reasonable prices. Good luck!!!
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Old 01-25-2020, 01:42 PM
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Gil's or any similar exhaust that does not mix water in until closer to the transom will be fine.
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Old 01-25-2020, 05:13 PM
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Originally Posted by PARASAIL941 View Post
731 cam works well in Mag motors. As far as exhaust , I ran early 420 six bolt riser exhaust ( Merc switched to Gil exh on late 420's), on my race boat for one season. Switched to Stainless Marine and lost over hundred pounds on stern , 10x easier to service motors , and could actually feel the weight difference in handling. These come up for sale in pairs frequently at very reasonable prices. Good luck!!!
what type of lifters are the safe ones to use with the cam? I had looked the cam up and say comp cams lifters but did not see good reviews. Whatís the reliable, preferred choice? Do I need to have any specifics on the valve springs as well?
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Old 01-25-2020, 09:48 PM
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Compís short-travel hydraulic roller lifter is good. And I believe Compís 953 spring is the right one.
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Old 01-26-2020, 01:49 PM
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Originally Posted by TomZ View Post
Compís short-travel hydraulic roller lifter is good. And I believe Compís 953 spring is the right one.
mis there anything I should consider with valves as I move toward doing these upgrades? Are stock valves acceptable or are there any thing necessary to improve longevity in this realm?
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Old 01-26-2020, 01:57 PM
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Unless youíre planning on supercharging it, the exhaust valves should be okay as long as theyíre serviceable. Freshen up the heads (make sure they are not rotted in the exhaust ports).

You could also ditch the factory heads and upgrade to EQ iron heads and pick up some power, though the intake ports may be a bit overkill.
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