disagree on the exhaust manifold... the biggest restriction in the entire intake and exhaust path is in the cylinder head in the intake and exhaust bowls and around the valve itself. Port matching won't net you ANYTHING unless you have a slight mismatch in your path. All opening up a port will do is slow down the charge. Your biggest gains are with bowl work and a nice valve job. That's with pretty much any engine, but these heads are especially restrictive.
I have run both stock and aftermarket and ported aftermarket manifolds on 12v trucks, and I honestly can't tell a performance difference between them.
I have also run unported and ported heads on 12v, and I noticed 200* EGT reduction and MUCH better turbo spool up with less smoke.
I have also run a compound setup and various singles, and I would prefer a nice Airwerks single turbo with a ported head and a camshaft over compounds and an unported head and stock cam.
the free breathing engine with a properly matched turbo will exhibit similar EGT's, far superior drivability, spool-up onset and needle-sweep time, and will probably make more power due to less exhaust restriction.
I went from an HX35-12w on top of an S400 with an unported head to a ported head with an sps62. didn't dyno with the twins, but the truck hit 40psi of boost about 300rpm SOONER with the single and ported head. the needle started moving 100rpm later (1600 instead of 1500), but it moved SO much faster. drive pressure was BELOW 1:1 at 55psi below 3000rpm. it was 1:1 at 48psi all the way to 4000rpm. I'd imagine drive pressure at 55psi from those twins breathing through an HX3512 would be in the 85+ range (hurting power)
I made 535rwhp with the single combo. Never had clutch problems w/ the twins because they didn't make a ton of boost below 2000rpm. when I went to the single, I would blow through the clutch in OD below 2000!
truck made 1196ftlbs to the wheels on the dyno taking it easy down low to not hurt the clutch.
EGT's were 200* higher w/ the single than the twins. A nice camshaft probably would have brought that closer in line and would have spooled the turbo even sooner than the twins!
from rotty: Well actually it does.
Try blowing through a small straw, see how much back pressure you get in your mouth.
Now try blowing through a garden hose, see how little back pressure you get in your mouth.
But notice how much more air you blew through the garden hose, same principle....
I was saying it made no sense to discount port work just because it's a turbo diesel and that the turbo had more of an effect than porting. I would certainly rather have a nice aftermarket turbo w/ a stock head than a ported head w/ a stock turbo, but if I was building a combo, I would CERTAINLY port the head (correctly)