I'm running this one. Internal diameter was 2.036" compared to the factory plastic one that measured 1.88" or 1.83" if i remember correctly. Looking at logs, I cant say for certain that I can tell a difference.
https://www.ecstuning.com/b-ecs-part...0757ecs09~ecs/
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2016 BMW 535i, MHD stage 2+, XHP stage 3, VRSF charge pipe, VRSF down pipe, VRSF intercooler, ECS turbo inlet pipe