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I don't want to stray too far off topic in this thread, but in a nutshell:
The presence of a turbo simplifies the exhaust design strategy, but it doesn't make things easier on the intake side. The intake is flowing a greater mass of air, but not a greater volume (only increased pressure), so the design criteria is pretty standard dry-flow port injected FI theory.
Where stock TF intake manifolds are concerned, they are fine for the mild street applications, and deliver good low and midrange torque. For high hp, bigger turbo (higher rpm) applications, the runners are too long/narrow and the plenum too small for big power. When people start talking about 50-trim T3/T4 and such, exchanging the stock piece for a unit with ported/shortened runners and gutted upper becomes a better option. The shorter runners exchange low rpm efficiency for improved high rpm efficiency, and the larger plenum volume is better suited for high rpm breathing. Users that go to large turbos, custom exhaust headers and high-flow heads with big cams and standalone ECUs will benefit further from intelligently designed, hand-fabbed intake manifolds with short, larger intake runners and large plenums.
Such a manifold looks like this:
The presence of a turbo simplifies the exhaust design strategy, but it doesn't make things easier on the intake side. The intake is flowing a greater mass of air, but not a greater volume (only increased pressure), so the design criteria is pretty standard dry-flow port injected FI theory.
Where stock TF intake manifolds are concerned, they are fine for the mild street applications, and deliver good low and midrange torque. For high hp, bigger turbo (higher rpm) applications, the runners are too long/narrow and the plenum too small for big power. When people start talking about 50-trim T3/T4 and such, exchanging the stock piece for a unit with ported/shortened runners and gutted upper becomes a better option. The shorter runners exchange low rpm efficiency for improved high rpm efficiency, and the larger plenum volume is better suited for high rpm breathing. Users that go to large turbos, custom exhaust headers and high-flow heads with big cams and standalone ECUs will benefit further from intelligently designed, hand-fabbed intake manifolds with short, larger intake runners and large plenums.
Such a manifold looks like this:
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