Exhaust manifold for BMW E30 6-cylinder — TA Technix

On a naturally aspirated engine, the manifold is the exhaust component that changes the engine's character the most, and the only one that works through pressure waves, not just flow. Equal-length tubes allow each cylinder to empty without interfering with the next one: cylinder filling improves, and with it, torque across a given rev range.

The design determines the power band: a 4-2-1 brings torque back into the mid-range, making it well suited to road use; a 4-1 shifts everything higher up and weakens the low end, which only makes sense with a camshaft and exhaust system to match. A sports manifold fitted on its own to a standard engine delivers a real but subtle gain - it is a component that should be considered as part of a complete setup.