I disagree, but it's not based on just being contrary. (Although I can be a disagreeable SOB at times...)
An engine is a pump. AzCoupe made a nice description on a three funnel anaology a while back.
Basically, any time you
a)improve cfm flow from zero thou lift to, say 450 to 550 thou, you gain power at higher rpm
b) if you do increase cfm flow without decreasing air speed (like you go for a bigger port but the air speed at zero, 450 or 550 thou is still the same), you gain torque at lower rpm
If just the head flows more efficiently via flow rate and still has fairly high speeds, you gain everywhere, even if the cam, carb and block are the same.
A turbo behaves no differently to a normally aspirated engine in this respect.
The manual iteration dyno prediction model I've used shows that a head flow is 1/9 th of the total picture on Horsepower and torque. A primo head may give a uniform 11% boost in power and torque, with no other alterations. But the valve sizes, manifold, and cam intensity with an X-flow head are much better, so in theory, a 33% boost on the log is possible. Even with puny 1.3" ports rather than the bigger log head ports, the alloy cross-flow is very, very efficent. Angled valves, optimised flame travel, and the great thermodynamic properties of the alloy casting makes it a huge asset.
Let me give you an example I'm experimenting with. Using a 230 thou steel plate on the stock 1966 200 log block. Shove any log head on it, and use just a taller Chevy/Holden L6 pistons to ensure the piston parks at the top of the block. One engine can now take a log, 2V, ME, or X-flow head, Krogdahl or even a SOHC or DOHC head with a bare minimum of modification . How it is done, I won't go into, but it basically takes the Jack Collins X (JCX) approach, but allows the splayed cross-flow pushrods to be accomodated without needing the block welded up at all. Everything is done via simple machining. Hence the rod ratio, bore size, deck register and compression is all the same since most stock X-flows are 53 cc's, and most modified big logs can go down to 53 cc with just a 40 thou shave. The head, intake, exhast and cam are the only variables. Ignition stays as a Toro-style belt driven Vertex magneto or Duraspark HEI set-up driven off the front crank.
Now lets run the prediction model. I've asserted that a 370 hp 200 cube engine is possible on 20 pounds of boost at 6.5:1 compression with two 2-bbl 350 cfm Holley carbs fed a pressurised supply from one turbo. A TO4 is better than a TO3 Super 60. The figures are with one large intercooler mounted on the top of the engine block, as per the RX-7 or Subaru set-up, only bigger.
Power is 370 hp at 5000 rpm, 440 lb-ft at 3700 rpm. This is based on a stock, non turbo Mustang Geezer style 200 six with modified E0 head with 175 hp and 200 lb-ft , with a 264 cam, but with 11:1 compression and twin carbs with an FSPP header. (When you turbo, you drop C/R, and get no free flowing header. The power increase is equal to 20+14.7 all over 14.7, times the air cooling efficency of 90 %. That's a 2.25 times power and torque boost. This is where the 370 hp comes from.
1 stock alloy head on this engine would give another 11% due to head design, 3% due to intake improvement, non from the same 350 carbs, no via the exhast header, but another reduction in detonation via the improved chamber design. In addition, the x-flow cam is differnent to the log cam, as the rocker ratio is 1.73:1, not 1.5:1. All up, lets say just a very conservative 14% at the non-turbo phase. That's 200 hp at 5000 rpm, but you'll only get a percentage of the torque becasue power is a function of torque. Net result, about 220 lb-ft at 3700 rpm.
As a turbo, it goes up as a proportion. Thats 420 hp, 485 lb-ft, as long as the cam is one which suits the cross-flow.
That's all I'll put my name to. Jack or some engineer with the engine analyser can prove or disprove.
The X-flow has very little threashold for detonation, but as a turbo, it is vastly better than the log head. I'll bet money the in any baseline combo, the x-flow head results in much more than a 14% power boost even at full boost. It's nothing for a worked 2V to add 33% to a stock 200, but the 2v swap is a manifold and carb and exhast swap, and nothing is a control test.
I could do some Excel graphs, and lock it down some more, but I'm certain the Engine Analyser will back it up, becasue it just models what I have seen in dyno runs from productionengines all over the world.
Hope that helps.
