You cannot say "hey, they get 756,34 HP" at 1.2 and I only get 654,72 HP". Boost doesn't mean power, it only means that effective air pressure in certain point where you pick up your boost signal is whatever boost gauge says.
Some people measure boost directly after turbo, others measure after intercooler, some measure boost in plenum. It's apples and oranges really.
You can build engine with same displacement/internals that makes more power at 0.8 bar than same engine with different intercooler/turbos at 1.2 bar. Boost doesn't say much at all. We went trough this in other thread not to long ago.
Power is made by moving certain mass of air trough engine. If there is lot's of backpressure and/or discharge temperature after turbo is high, you'll make ton's of boost but less power.
Second: I really don't see the the reason why ITB's should make 40HP gain. It's just a throttle. Once you floor it, those butterfly's will open to 90-degree and just sit there in airflow. Even if you use ITB's, they will be siamesed into common plenum fed by simple pipe. Double that with twin turbo. Theoretically, it won't matter where you put your throttle as long as it's diameter is in line with rest of tubing.
It will improve throttle response somewhat (and make tuning and adjustment a nightmare), but I'm kind sceptic about ITB's themselves making high power gains. Once you WOT it, throttles "shouldn't be there".
I believe that in reality, most of ITB gains actually comes from the fact that mounting ITB's often lengthens the intake tract (by it's sheer complexity) which in turn tunes intake better.
With other words, you can probably make same result by using optimally dimensioned single throttle and play with intake runner length.
Third: making more than 600-700hp from 3.4L engine will cost arm and leg and won't necessarily improve real world speed (on track). It's a point where OEM stuff isn't up to snuff any more and you are forced to swap internals for custom parts at alarming rate.
Rockers must be changed to solid "RSR" ones, pistons get too heavy for the revs, twin plugging is a must, rods are too weak and has to be changed to H-beam ones, headers demand very elaborate design, turbocharger must be custom tailed (and new design), intercooler must be big and fit, whole intake must be redone to avoid sharp bends, fan must be overdriven so it can keep heads cool, generator moved from the fan (as it will fail and chew belts when overdriven) etc.
Speed is money...how much?
