400M with overbore
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Joined: Dec 1999
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From: New Orleans United States
400M with overbore
While rebuilding my 351M in my 77F150 4X4, i noticed that the motor mount bolts holes had cracked. So I ran to NAPA and picked up a 400M short block that came with a .060 overbore, which i didn't request. The engine is running an Edelbrock cam with 224 degrees at .050" lift, a weiand intake and a holley 750 with vacuum secondaries (it's great when you stomp it and they open up). My question is if I should worry about that pesky overbore being a weak link. The engine is hooked to a C6 and happily spins to 5000 rpm before shifting when racing those pesky camaros and "offroad" Z71's. I wonder how much extra they payed for those decals and nothing else on the option list? I know that the M series is a thin walled engine already, but how much protection do I really have left now?
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400M with overbore
Big red,
the concern with that much overbore in a thin-wall casting will be overheating. I have known of guys running .040 over with no problem but I do not personally have experience w/ one .060 over.
If it were me, I would run at LEAST a good 3 core or even 4 core radiator and keep that thing cool.
To my knowledge, 351m400's cast at Michigan plant around or before March 1977 had cracking problems in the lifter valley area.
If you keep it running cool, that thing should rock!
Rick
the concern with that much overbore in a thin-wall casting will be overheating. I have known of guys running .040 over with no problem but I do not personally have experience w/ one .060 over.
If it were me, I would run at LEAST a good 3 core or even 4 core radiator and keep that thing cool.
To my knowledge, 351m400's cast at Michigan plant around or before March 1977 had cracking problems in the lifter valley area.
If you keep it running cool, that thing should rock!
Rick
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400M with overbore
Big Red,
I just had my 400 bored .040 over...I had the same concerns you do/did. After talking to my machinist he assured me that the 400's would be good up to .060...so, just don't run 'er to hard and keep 'er cool! You should be okay...
I just had my 400 bored .040 over...I had the same concerns you do/did. After talking to my machinist he assured me that the 400's would be good up to .060...so, just don't run 'er to hard and keep 'er cool! You should be okay...
