On a naturally aspirated engine, the manifold is the exhaust part that changes the character the most, and the only one that works through pressure waves, not just flow. Equal-length tubes allow each cylinder to empty without hindering the next one: cylinder filling improves, and with it the 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 bottom end, making sense only with a camshaft and exhaust system to match. A sports manifold fitted alone to a stock engine delivers a real but subtle gain - it is a part that should be considered as part of a complete setup.