With diesel fuel prices at an all-time high, we've been testing various products in an effort to find ways to increase the efficiency of the diesel engine. Our hope is to find results that will offer better fuel economy, and if possible, increase torque. Most of the products we have tried up to this point have offered some positive results, and some products have worked better than others. Many of the products available are not by any means light on the pocketbook, and some are beyond "plug and play" installations, requiring professional, or at the very least, a skilled installation, which can add to the cost. If anything, we have reinforced the old adage "If it seems too good to be true, it probably is."
Recently, we had the opportunity to spend some time with Piers Harry, formally of Piers Diesel Research. He mentioned that before he left PDR he had developed a camshaft grind for the common rail '03-and-later Cummins-powered Dodge trucks, which resulted in a fuel economy increase of about 2 mpg and maybe picked up a horsepower or two. We know what you're thinking. If obtaining better fuel economy can be found from a different cam grind, why didn't Cummins do it? The answer is that the Cummins Engine Company has to abide by federal emissions guidelines, and you, the end user, may not.
After we had the new cam broken in, we took a road test to see how it felt. Right off, we noted the sound was more like the older 12-valve Cummins; not as loud, but there was a new pleasant tonal quality. Swapping the camshaft in a Cummins engine is not what we'd call easy. The process developed by Cummins borders between genius and insanity. For those not familiar, it involves slotted semi-circular metal trays, wooden dowels, magnets, strings, and rubber bands. This is not your typical backyard shade tree installation. As if that weren't enough to discourage most, the entire front of the truck has to be dissembled (including taking a Sawzall to the radiator support) to permit access to remove and install the new cam.
In order to meet the '03 nitrogen oxides standards, combustion cylinder pressures had to be lowered. One way to accomplish this goal is to retard injection timing, thus reducing cylinder pressure and reducing nitrogen oxides (one of the design functions of the OEM camshaft). The Catch 22 is that it takes more fuel to operate in this manner. But what if you could convert to a camshaft that was fuel economy biased instead of emissions biased? We wanted to find out.
 Once the intake, exhaust manifold...  Once the intake, exhaust manifold valve cover, rockers, and pushrods were removed, wooden dowels were inserted into the lifters. The dowels and rubber bands kept the lifters from dropping into the engine when the cam was removed. |  When the cam came out, a round...  When the cam came out, a round metal tray was inserted into the space where the camshaft was. Then the wooden dowels were removed, dropping the lifters into the metal tray so the lifters could be removed from the engine. | |
Fuel Economy Testing
What will all this do for our fuel economy? In an '05 Quad Cab 4x4 with the G56 six-speed manual transmission and 3.73 gears, we have established the following: our unloaded truck fuel economy averaged 15.8 mpg and towing averaged 9.4 mpg.
Keep in mind that our test truck weighs 7,240 pounds even when it's unloaded. Towing was accomplished by pulling a 24-foot Haulmark enclosed car hauler. The gross combined weight of the truck and trailer is 22,800 pounds. We logged approximately 9,800 miles empty, and the balance of the first 15,000 miles towing established our baseline.
First, we ran the short track empty (approximately 150 miles), then the short track towing, followed by the long track empty (approximately 700 miles), and the long track towing.
During that time, we found that driving our Cummins-powered Ram with the PDR cam was a pleasure. We saw that there was an average fuel economy increase of approximately 2.1 mpg across the board. The results remained consistent towing or empty, city or highway.
PDR has two options for the new cam: one is an all-new camshaft made from a billet cam blank, the other is a regrind of the OEM camshaft. Each offers its own benefits. The billet cam is purchased outright, and the regrind requires a core deposit ($447). The billet cam has the additional lobe required to drive a mechanical fuel-injection pump if you were inclined to convert a 24-valve engine to a P7100 injection pump.
The timing gear is a heat/press fitting and a hydraulic press is required for removal of the gear, which was reused on the new camshaft.