How much horsepower can you gain if have dual exhaust installed in your 2008 Ford F150 5.4 L?

You'll likely gain very little, if any, horsepower from installing a dual exhaust system on your 2008 Ford F-150 5.4L. While a properly designed exhaust system *can* improve flow and potentially increase horsepower and torque, the gains on a naturally aspirated engine like the 5.4L in that truck are usually minimal – we're talking perhaps 5-10 horsepower at most, and possibly none at all.

The biggest benefit of a dual exhaust system is usually improved sound and potentially slightly quicker exhaust scavenging (helping with engine breathing at higher RPMs), but the power gains are rarely significant enough to be easily measured on a dynamometer. The stock exhaust system is usually already fairly well-designed for the engine's power output. Larger gains would come from other modifications like engine tuning or forced induction (turbocharger or supercharger).