Decking 400
Lead Driver
Joined: Nov 2000
Posts: 6,647
Likes: 352
From: Albuquerque
The stock 400 piston will set "way" down in the cylinder. At least .250. It's much higher on the 351M. If you go past .030 total on heads and deck you may have sealing problems on the intake manifold unless you compensate it's sufaces.
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
All OEM 351M and 400 pistons were dished.
BTW: For some time, the '71 400 was said to have flat-top pistons, which explained its higher compression ratio and power rating, but the original pistons that I pulled from a 1971 400 had a very slight dish (about 4.5 cc).
BTW: For some time, the '71 400 was said to have flat-top pistons, which explained its higher compression ratio and power rating, but the original pistons that I pulled from a 1971 400 had a very slight dish (about 4.5 cc).
Laughing Gas
Joined: Feb 2003
Posts: 1,234
Likes: 3
From: In the woods of Oregon
I suppose if we deck the block enough to get quinch with the stock pistons, that the compression ratio would be to high. Can u even get quinch with the open chamber heads?
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New User
Joined: Dec 2003
Posts: 4
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Thanks for the info, that is exactly what I was looking for. I want to shave heads/deck to come up with 8.7/8.9 to one compression. As I understand it, anything over .020 and the intake needs machining.
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Elder User
Joined: Nov 2003
Posts: 705
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From: Okla.
I took out .107. .035 off the bock amd .072 off the heads. NO problem gitting it to seal. BUT it will not run on chep gas. And I'm running 351W push rods to keep valve trane lined up right.And if you deck the heads DO NOT cut on the intake, take the same amount off the intake side of the heads. This way the intake will wark with other heads not just that set. My piston set in hole at .006. Just my 2 bits.
Last edited by 74 F100 351m; Jan 22, 2004 at 09:28 PM.