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

Answer 1

There is no set number gain. There is more to it than just putting on duals. You need to change the air filter to a more free flowing type like K&N etc and not just the replacement filter itself. You need to change out the whole stock air box. Now problem 2, you really can't put true duals on it unless it has a factory option for duals in that model AND has cats for both sides. Its against fed EPA laws to change it. Now you can do a cat back exhaust and split it. My muffler guys all use a single, large tube exhaust. I use the same on my V-10. Different exhaust manufacturers will have some dyno results on their exhaust with different models of vehicles.