DARCY RACING IS NOW OFFERING TRUE BILLIT TwinCam HEADS FROM 11" ROUND X 3.9 THICK 6061-T6 BLOCKS. DESIGNED WITH PERFORMANCE AS THE MAIN GOAL. THESE HEADS FEATURES A RAISED INTAKE PORT AND A "D" SHAPE EXHAUST PORT.  WITH THE USE OF CADCAM DESIGN AND MACHINING SOFTWARE, THE COMPLETE HEAD, INCLUDING THE PORTS ARE COMPLETELY 5AXES CNC. MACHINED ,WITH A VERY MINIMUM OF HAND DETAILING REQUIRED UNDER THE VALVE SEAT. THE PORTS ARE DESIGNED FOR MAXIMUM VELOCITY AND FLOW FOR THE LONGEST POWER CURVE. AMPRO/BRONZE GUIDE AND 2.0/1.610 SS PM VALVES ,TOPPED WITH DRS VALVE SPRING KIT GOOD TO .625 LIFT. HEADS COME MACHINED FOR HARLEY-DAVIDSON ELECTRICAL COMPRESSION RELEASES AND DUAL SPARK PLUGS HEADS STILL USE YOUR STOCK MANIFOLD.  MOST CNC PORTED HEADS ARE FIRST DONE BY HAND UNTIL SOME BODY DECIDES ITS GOOD .THEN THEY ARE DIGITIZED(A PROBE GOES 2D OR 3D INSIDE THE PORT SO A PROGRAM OF THAT PATH CAN BE SET UP FOR THE CNC). I HAVE DONE THIS MANY TIMES AND STILL DO, HOWEVER HAVING THE ABILITY TO DRAW THE PORT ON THE COMPUTER  TO THE PERFECT SIZE AND SHAPE THOUGHT THE COMPLETE PORT IS MUCH BETTER.