Although an aftermarket exhaust system will benefit vehicles of any engine type, diesels (and in particular Powerstrokes) stand the most to gain. Whereas aftermarket exhaust systems are geared primarily toward making power and improving sound, putting one on a Powerstroke Ford can yield some surprising increases in performance potential, reliability and fuel economy.
In and of itself, a bolt-on catalytic converter back exhaust system is good for about 20 horsepower over the stock arrangement. The gains will vary depending on the type of exhaust system (dual or single), the tubing diameter and muffler, and will generally occur in the upper end of the engine's RPM band. This upgrade is so popular, cheap and effective that it seems difficult to find a Powerstroke without one. Replacing the turbo down-pipe in addition to the cat-back system is good for another 4 to 8 horsepower on stock trucks, but performs a more important function than any out-of-the-box power increases it may yield.
The primary benefit of an aftermarket exhaust system is that it's a necessary step toward adding huge power with other bolt-on upgrades. Powerstrokes live up to their name with their massive power potential, but no amount of airflow or fuel is going to help without getting rid of spent gases. Combining an aftermarket exhaust with a free-flowing air filter and computer chip to increase boost levels is good for more than 100 horsepower on many Powerstrokes, with little more than a couple of hours of work. This is a claim that very few engines can make.
Injecting more fuel and increasing boost to make power is as easy as reprogramming your stock computer, but it does create one serious problem. Without a free-flowing exhaust, a certain amount of still-burning fuel will make its way into the turbo, causing it to overheat and eventually fail. An aftermarket down-tube and exhaust will drastically decrease exhaust gas temperatures, allowing you to run more boost without overheating the engine or turbocharger.
An aftermarket exhaust system will allow any engine to more efficiently eliminate exhaust gases and get better fuel economy, but the gains to a Powerstroke are simply incredible. By itself, an aftermarket exhaust system and down-tube are worth about two to three miles per gallon, but gains rise to a whopping five to six mpg when combined with a free-flowing air filter and computer tune. Though this wouldn't be an impressive feat on most cars, most Powerstroke-equipped trucks only get 10 to 12 mpg in the city and 14 to 15 on the highway in stock form. That's an incredible 50 percent increase in the city cycle and about 30 percent on the highway. So, is a 50 percent decrease in fuel economy and 30 percent decrease in power worth having a quiet exhaust system? It's up to you, but the vast popularity of exhaust and intake upgrades on these trucks should speak for most people's opinions.
