I have been told a figure of approx. 190cfm per inlet port at 10 inches of water. I have also been told that without too much effort they can be made to flow 230 cfm without changing valve size. I was also told that porting on the exhaust side did not make much of a difference in power.
The engine that that I have seen which had the ported head that flowed over 230cfm/port has achieved over 230kW @ the wheels with the standard turbo, 272i, 264e cams and running just under 1.5 bar of boost with an autronics ECU. The car has pulled a high 11 1/4mile which seems to give credibility to the dyno figure.
To me the theory of minimising flow resistance and pumping losses through the port is sound whether the engine is forced induction or NA.
I've just fitted a Stage 5 (yes, I know all this Stage business is pure marketing, but anyway...) head on my Evo 5. Apart from the usual porting and polishing, it also has larger valves and titanium retainers, though keeps the stock valve springs. I bought the head off a friend's Evo (that car dyno'd at 380HP @ the wheels with a bigger turbine and 1.7 bar boost. Pulled 11's in the 1/4 mile), as he was selling the car.
I don't know what the precise flow characteristics or specs of the head are, but I do know it has resulted in a measurable increase in power. By simply slapping the head on, I have gained 20HP @ the wheels, achieved at a LOWER boost level than before. This is with a stock ECU, and I'm hoping to find another 15-20HP (fingers crossed!) once I've fitted a proper programmable ECU so that I can remap to run at around 1.2 bar on the stock turbine and internals.
Will certainly do so. I hope to get the new ECU next week, so with any luck, I'll have the car back on the rollers and tuned before end-April.
NO QUESTION though that the head has already made a difference. In addition to what I've already stated above, my power curve is much nicer now. On the stock head, I was hitting peak power of 234HP @ the wheels at 6000 RPM, and then the power would drop off precipitously, such that by just over 7000 RPM, my power was down to about 190HP. This was at between 1.0 and 1.1 bar peak boost.
With the new head, the power just keeps on coming past 6000RPM, peaking at 253HP @ 7000 RPM. So you can imagine how this improves the fun of driving the car, since it now truly makes sense to rev all the way to redline. And keep in mind this is now achieved at 0.9 bar boost.
So you could almost argue that with this head (plus your standard intake and exhaust mods,) I've achieved an additional 40HP @ the wheels over a bone stock Evo, at STANDARD boost levels (0.9 bar). Note I say 40HP over stock, because on my tuner's dyno, bone stock Evo's normally produce between 210 and 212HP @ the wheels.