The Holy Grail for many hunters and fishermen isn’t an in-your-face largemouth that straightens a 2/0 hook or a big whitetail that makes the book. It’s a 4x4 with more power. Guys who push a four-wheel-drive pickup or sport utility to the limit by climbing high mountain offroad trails or horsing a boat and trailer off a steep, muddy boat ramp have learned that modern 4x4s all too often come up a bit short in the power department.

But extra power sometimes comes at a hefty price. A turkey hunting buddy put it to me point blank: “I want more power, but I don’t have the budget or the time for a complete engine overhaul or really expensive accessories. What can I do?”

As it turns out, plenty.

By focusing on the exhaust side of the engine, you can give a 4x4 much more seat-of-the-pants performance at a price you can bear. The reason exhaust modifications can pay off so handsomely is because engine performance boils down to combustion efficiency. For an internal combustion engine to make power, it must efficiently convert fuel into heat (power). How well it does this is a measure of its combustion efficiency.

Combustion residuals (exhaust gas) that are allowed to remain in the cylinders after each combustion process reduce efficiency, which translates into a loss of power. But if you can rid the engine of exhaust gas faster, you can increase the efficiency of the engine--and that means more power, better fuel economy, and improved driveability. Longer engine life can also result. All in all, pretty good benefits.
           
Head to Toe: The greatest gains will come from replacing the engine’s stock exhaust manifolds with headers. “Original equipment exhaust manifolds tend to compromise combustion efficiency, primarily because the factory needs to design vehicles for a very wide range of applications,” says Steven Anderson, special accounts manager for Flowmaster, an aftermarket muffler company. “When it comes to the specific uses that interest your guys--for example, heavy hauling, towing, low-range four-wheel-drive, and high-altitude operation--the factory manifolds can work against you. But aftermarket headers can change that.”

What exactly do headers do?

“One of the biggest obstacles to better performance is back pressure, which is the unwanted result of the system’s inability to remove sufficient spent gas,” says Anderson. “Back pressure causes some of the restriction in exhaust gas flow, as does the design of the stock manifold itself. Typically, a properly designed header is an arrangement of individual pipes that lead from the exhaust ports into a common passage, which eventually enters a muffler. Exact pipe size and length not only help determine how much but where in an engine’s rpm range power improvements are provided. Obviously, for trucks it needs to be in the lower range, below 4,500 rpm, where sportsmen need it most.”