"Is the airbox restrictive, and does a cold-air intake (CAI) actually help?" is one of the most-asked E36 questions, and the honest answer is: on a naturally-aspirated E36 (M50/M52/S52), an intake is mostly sound and a small top-end gain, not the transformation the marketing implies. The stock airbox breathes better than people think, and what actually matters is a cold air source and not upsetting the MAF
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