Tuned inlet lengths and diameters remain important with particularly with naturally aspirated engines. In this case the new, larger diameter, throttle body is from a turbocharged engine therefore the parameters would be quite different. The increased size of the throttle body may increase the power at the top end but in combination with the sports exhaust system and the different air filter would almost definitely only give the best results with a re-map and, in fact, may reduce the peak power. One should not assume that the re-map for the sports exhaust system would be sufficient. I don't know how the ECU is set up but I would suspect that at full throttle and high revs the system is not utilising the closed loop feedback but working purely on the fuel map. In order to get the best power output and to protect the engine this is normally set slightly richer than the stoichiometry air–fuel ratio used for emmision requirements and fuel economy. In the worst case such a change may lead to an excessively lean mixture at wide throttle openings and burn a hole in the piston or damage valves etc. The functioning of fuel injection on a GDI engine is very complex and relies on multiple micro pulses of fuel injected into the cylinder in order to ensure a thorough mix of air and fuel for the combustion process. In effect it is poorly burned droplets of fuel that cause fine carbon particle output on GDI engines that in some case may exceed the fine carbon particle output of diesel engines.

A larger diameter inlet tract could also reduce the velocity of the intake are at intermediate rpm. The result of this would be to reduce the intake flow into the cylinder as the valves open. In other words reduce the charge entering the cylinder. This in turn would reduce low and midrange torque.

I recall a Honda car 4 valve engine that only operated one of the two inlet valves once a certain RPM had been reached. This was specifically to increase intake velocity, and therefore cylinder charging, at low to intermediate RPM, in order to improve torque in that regime.

Mind you I'm not a qualified automotive gas flow engineer so all the above is probably a load of tripe.

Peter

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