For a 1650 you will want about a 2.1-2.4 sq inch port (depending wether you are drag racing or LSR) at the mcsa at 2.5" from the valve with a 1mm os valve with the throat at 89% and an overall taper increase of a few %. This combo will put the port velocity at about 310fps @ 28" and flow around 295 cfm at 28", the seat or "window" velocity will still be much higher than stock even with 1mm o/s size valves so trapped volume will be excellent even with huge cams.
Its possable with a stock casting, we have done a few, but its VERY easy to get into water and the spring seat. So the port needs to have a bent roof. You will need larger throttle bodies to maintain good overall taper. The heads also need to have bronze seats to make the valves last and should have bronze guides.
The stage 3 CNC program took quite a while to develop, and we had to sacrifice a cylinder head to the bandsaw to really get a good look inside to make certain the head would be durable. So far we have had excellent feed back on power and durability.
Excessive rod angle is the biggest problem.
A 1650 should be in the 265-275 range. The stage 3 full CNC head is about $2500 complete built on you're core.
