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