400 head work for diy
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Elder User
Joined: Jan 2004
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From: Eastern Pa
400 head work for diy
I'm working on my heads now. Are there any specific things to be aware of or pay attention to with these heads. The intake port other than needing to be matched up with the manifold and softening the guide boss doesn't seem to have much wrong with it. There doesnt appear to be a whole lot to be removed on the short side radius because the water jacket is pretty close. (better safe than sorry) The exhaust has the thermactor bumps. Any wisdom out there specific to the 351m/400 head?
Tuned
Joined: Jul 2003
Posts: 455
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From: Berkeley
when i had my '82 400 heads done, we polished the exhaust port after removing the thermactor bumps. polishing the combustion chambers to minimize detonation resulted in about 80cc and ~8.8CR with badger flat-tops ~.07 in the hole.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Don't match the intake port with the manifold. The manifold must be smaller then the intake port for proper flow. Usually all that is required is cleaning up any casting flash and irregularities.
Polish the combustion chambers but be carefull not to remove too much metal. Polish the exhaust ports and remove the thermactor bump. Have your heads cc'd and then mill the heads to match up the volume. You may have to do more polishing after some more metal removal to match the chambers. Mill the block as required for final compression ratio. 9.0 +/- 0.2 is great. Have the manifold milled to match the heads and block. Mark the manifold, block, and heads for the amount of material removed with metal stamps. Mark the final head cc's also. Check everything for proper fit.
btw- The exhaust ports need to be smaller than the header or manifold ports too. Remember also that things may not quite bolt together the same way twice and no two gaskets seem to be alike. Even the same brand same lot may have been punched on a multiple die.
Polish the combustion chambers but be carefull not to remove too much metal. Polish the exhaust ports and remove the thermactor bump. Have your heads cc'd and then mill the heads to match up the volume. You may have to do more polishing after some more metal removal to match the chambers. Mill the block as required for final compression ratio. 9.0 +/- 0.2 is great. Have the manifold milled to match the heads and block. Mark the manifold, block, and heads for the amount of material removed with metal stamps. Mark the final head cc's also. Check everything for proper fit.
btw- The exhaust ports need to be smaller than the header or manifold ports too. Remember also that things may not quite bolt together the same way twice and no two gaskets seem to be alike. Even the same brand same lot may have been punched on a multiple die.
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
When Hot Rod built their 470+ HP 400 they did extensive head work especially on the exhaust side. They completely removed the valve guide boss that was in the pocket to open up the exhaust.
Also pay close attention to the area around the valves. You can remove material there to reduce valve "shrouding".
Also pay close attention to the area around the valves. You can remove material there to reduce valve "shrouding".
Senior User
Joined: Oct 2003
Posts: 347
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From: in a house
on the thermactor bumps(smog bumps) I have a few q's.
whenever an M block project comes up, the first thing to go is all the emisions equipment prior to installing headers and aluminum intakes.
I have yet done any extensive porting other than smoothing out casting roughness or imperfections but I have noticed that sometimes none, all or only certain bumps are drilled. why is this? is this any reason to all the differnces in performance #'s for these engines?
also, are all the air passages including the crossover safe to leave open? they only lead to the exhaust side so I would think no harm can be done.
whenever an M block project comes up, the first thing to go is all the emisions equipment prior to installing headers and aluminum intakes.
I have yet done any extensive porting other than smoothing out casting roughness or imperfections but I have noticed that sometimes none, all or only certain bumps are drilled. why is this? is this any reason to all the differnces in performance #'s for these engines?
also, are all the air passages including the crossover safe to leave open? they only lead to the exhaust side so I would think no harm can be done.
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