Trick Flow took a standard 4.6-liter Modular head design and did some wild things to it -- the most obvious part is that the intake valve sits on the opposite side of the head. This enables the valve to have a straighter shot into the combustion chamber allowing for a .650 lift cam and increased airflow. They employed the same "Twisted Wedge" technology to the Modular, and gave the head a big power potential where few others have dared to play.
The next change is the removable cam journal and cap. If you ever run into a cam problem, you can now replace it without junking your head. There is also a .750-inch thick deck and longer spark plug hole for added reinforcement. They offer the heads in 34-38cc combustion chamber sizes to accommodate everything from a 1992 Lincoln to a 2004 Mustang. This heads flow almost 250 cfm on the intake and 183 cfm on the exhaust, as cast, but expect a number of CNC porting options.
Check out their site at:
http://www.trickflow.com