1 more cyl head question

[s55mercury66]

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.

[FFR428]

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.