Thread: 1 more cyl head question

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I have a question about FE cylinder heads. Which is the best head? I have C4AE, C6AEU, and the D2 truck heads from '70's. I understand my C6 and D2 castings are identical castings except for hardened valve seats, but do the C4AE heads flow any better? Thanks.

The C4 heads are the earlier lowriser castings. A inexpensive favorite of many and respond well ported with larger valves. These also only have the vertical 8 bolt exhaust pattern. The C6-U and D2-AA heads are the later bread and butter FE heads for cars and trucks. Those are the velocity port design for reduced emissions. Those can be the 8-14 or 16 bolt exhaust pattern and have raised exhaust ports compared to the earlier C4 heads. Depending on what intake and exhaust manifold you want to use would also be a factor. So a little more info would be helpful here.