Not familiar with the stock ECU, but it should
compensate for the extra airflow (someone that actually tried this using a stock ecu will hopefully come in and correct me if I'm wrong).
About 400 crank hp on an RB26 should be as easy as:
1. Remove the boost limiter in the line to the boost solenoid, should get you to 14 psi.
2. Make sure the air filter isn't clogged.
3. Run it on premium gasoline and adjust the ignition, watch out for detonation
It's when you try to get past 450-500 that all your money does a magic trick and disappear
Some moneypits I've found VS power output...
At 450-500 hp
, you need bigger injectors & AFM's or MAP sensor (+ ecu to handle this), boost control & aftermarket air filter. Start worrying about the clutch too..
At 500-550 hp
, you should consider forged internals & reinforced head gasket, you need bigger turbos & bigger exhaust
At 550-600 hp
, you need a bigger fuel pump & fuel pressure regulator, also think the stock ignition system will start to fail around here.
Throw away that stock intercooler, get some badass camshafts, happy boosting!
Then there are a lot of other things to consider, depending on usage and where you live:
-External oil cooler
-Better oil pump & water pump
-Swirl pot for safer fuel delivery
-Break system upgrade
Those things are on top of the "to-do" list if you intend to track the car and push it hard, 3 things that kills the engines are overheating, bad lubrication & a bad tune.