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Discussion Starter #1
Why does this not work?

I have read many times the you can put a 5m or 6m head on a 7m but you can't put a 7m head on a 5m or 6m...Why is this????
 

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the first question you might want to ask yourself is why would you put a 7m head on a 5m/6m block....? just use a 7m block its better.
 

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Then way doesn't everybody just do that instead of putting 6m's in them. I would think putting a head with 4 valves instead of two would be great on any 5m or 6m engine and could be done with out having to pull the engine but if the head won't work and the intake from a 5m or 6m wont work then there would be no use. I just want to know why the head won't work and what is different about how the intake bolts up.
 

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The inlet manifold bolt pattern is quite different. I doubt you'd see many gains swapping a 7M-GE head on a 6M bottom end if there weren't any other changes (ie inlet system, ignition, electronics are all different on the 7M). Remember there is only 10hp difference between the 6M and 7M.
 

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Whats the Jap rated hp on the 7mge? There was always a 5 to 10 hp difference with the 5ms between NA and Japan, I imagine theres a difference for the 7ms too. Anyways, theres no point putting a 7m head on a 5m or 6m bottom as the only real difference between the 7m bottom and 6m bottom is the valve reliefs in the pistons.
 

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different valve relief cuts in the top of the piston. 5/6mge have piston cut for 2 valve heads, 7mge pistons have relief cuts for 4 valve heads. Blocks are alomost identical according to my engine consultant.
 
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