SBC 400 heads to a 350 head exchange question
 

My heads have leaky valve guides and does not have harden seats. I have a fresh set of 350 truck heads and was thinking about putting them on my 400 block. What do I have to change ? ie: what Head gasket do I use a 350 or a 400? What about the stem holes? The 400 heads are out of a 1970's car and the 350 heads are out of a early style 350 ( larger holes for the assories) truck. I know i will have to drill out my brackets but mostly don't know what gasket to use. Any help or insite would be great

Rick

Use the old 400 gaskets as a template to drill the steam holes in the 350 heads and install with new 400 gaskets

Felpro makes a marine performance head gasket for the 400 heads. I did the same thing on my engines. I built a pair of 409's out of a my old boat anchor 406's. The part number 17031 comes to mind but be sure to verify that.

What cam are you using. I had two sets of 400 heads that had the same problem. The exhaust seats were also getting pulled in. I used the COMPCAM Extreme Marine XM262H cam. And ported and polished World Torquer II heads. I'm really happy with the results.

from what i can remember you have two options. you can drill the steam holes in the 350 heads or plug the steam holes in the 400 block. i thought someone told me by plugging the steam holes in the block it actually strenghthened the block somewhat. i always thought you used the head gasket that matched the block(ie bore size) not the head.


my 2 cents Rob

The steam holes on my blocks were plugged the nut that built them originally. And badly at that. But they are so small less than an 3/32 of and inch I don't think they would make much difference. But they do help from getting a hot spot between the bores of the saimeesed bores. I had 350 heads drilled to match the 400 blocks and the hole in the blocks opened back up and used 4.200 bore gaskets for the 4.165 bores I was running. A standard 400 is 4.125.