2004 Ford F250 - Driveway

Diesel engines are essentially air pumps until fuel is added, so it makes sense that more efficient airflow is a plus. By installing a high-flow intake and exhaust, most diesel enthusiasts will see improved boost pressure that leads to more power and better mileage. This '04 F-250 Power Stroke had been around the block a few times, so it was fully broken-in, had reliable fuel-economy figures, was using the latest software updates, and featured a slew of aftermarket parts under the hood. It had run a computer programmer in the past, but for this test, the software was left stock. The truck frequently pulls a 10,000-pound box trailer and runs about 30,000 miles a year. The observed fuel economy with the current setup was 14.7 mpg in the city, 17.0 mpg on the highway, and 12.1 mpg while towing.

After shopping around, we decided to install a Volant cold-air intake along with a free-flowing, 4-inch exhaust by Diamond Eye. We did each installation separately to highlight the improvements of each step, beginning with the intake. The photos in the Volant instructions made the installation quick, and we were testing the new parts in no time. Noise levels inside the cabin and outside hadn't changed much, the turbo spooled-up a bit quicker (especially at altitudes higher than 4,000 feet), and throttle response was improved. The fuel mileage went up when the truck was working hard, so city-traffic figures remained close to 14.7 mpg, the highway mileage went up by 0.8 mpg, and towing numbers went up by 0.7 mpg.

After a few tanks of fuel were used, we installed the exhaust. A Sawzall is helpful, but a strong forearm and a hacksaw will also work. The Diamond Eye kit features a louvered muffler that can be installed in either direction. For a deeper, quieter tone, install the cups open toward the engine, and for a louder, higher pitch with more turbine whine, just point the cups facing the back. Call us wussies, but we went for the quiet setup. Testdrive your Power Stroke after the exhaust installation to make sure everything's tight and won't tap a fender, mudflap, or any other parts while you're bouncing down the road.

Unless you're under compression braking or the right-side windows are down and you're against a sound wall or next to a semitruck, the exhaust is no louder inside and produces a slightly deeper hum on the outside. We felt another incremental increase in throttle response and measured better fuel economy with 15.2 mpg in the city, 18.2 mpg on the highways, and 13.0 mpg while towing.

In addition to increasing the mileage of our Super Duty, the intake and exhaust upgrades improved throttle response and made the 6.0L feel stronger. To prove the upgrades were being sent to the rear wheels, we had the staff at Los Angeles Performance Division run it on the dyno. It turns out that about three hours of labor and less than $1,000 in parts was good for a gain of more than 9 hp and 20 lb-ft of torque (both at about 100 rpm quicker than stock). The combined mileage increase is sufficient enough that the parts will pay for themselves in a little more than two years, assuming 30,000 miles per year at $3 per gallon for fuel. We also expect to see even more power when the engine is programmed to take full advantage of the new free-flowing intake and exhaust. More power and better mileage in less than one day-what are you waiting for?