Mv 4v comment was more of a general statement/guideline. Out of the box (comparing stock-to-stock) 4V heads will flow much better than any stock 2V head. I will have to check out that group, Fordman...sounds awesome.

I've been doing some research and have found that the 2v 4.6 has a problem with leaking headgaskets under boost, but it seems that the 3v and 4v motors don't have this problem. Is it the design of the 2v heads that causes this problem?

A 4.6L head has cast-in journals with a removable cap (for Windsor engines) or a removable cap ‘girdle’ (for Romeo engines). The cams ride directly on the journals. If the valvetrain fails and the journals are damaged, the heads will function like aluminum doorstops.

The flow numbers I've seen on 4V heads suggests that TFS heads are close to stock 4V heads. Ported, a 4V head should be far superior. Bear in mind that C heads (99-05) are typically better, unless running high boost. The flow numbers I've seen on 4V heads suggests that TFS heads are close to stock 4V heads. Ported, a 4V head should be far superior.