5.9L Vs. 6.7L Cummins Diesel Engines - Cummins Vs. Cummins

A lot has changed since the 5.9L Cummins B-series engine was first offered in '89 Dodge pickups. The injection systems, cylinder heads, emissions equipment, and turbos have all seen dramatic improvements over the last 20 years. However, the one thing that Cummins has never altered was the displacement. During the same time period, General Motors upsized its diesel from 6.2L to 6.5L, and then to the current 6.6L engine for the Duramax. Ford sold 6.9L, 7.3L, and 6.0L in the past, and currently sells 6.4L Power Stroke engines, continually improving in order to meet various performance, fuel economy, and emissions requirements.

Yet while the number of valves and injection systems have been updates on the Cummins B-series, the engine has always displaced a consistent 5.9 liters. Of course, all of that changed last year when Cummins revised the B-series in the face of increased emissions controls for diesel engines. The new 6.7L B-series engine has 12% more displacement, advanced electronics, a variable geometry turbocharger, and is saddled with an EGR cooler and diesel particulate filter.

5.9L VS. 6.7L On The Dyno
We wanted to see how the 6.7L stacks up next to the proven 5.9L, so we rounded up two stock Dodge trucks equipped with four-wheel drive and automatic transmissions. The 5.9L Cummins truck was an '06 Quad Cab shortbed, and the 6.7L Cummins was an '07 Mega Cab. We began by putting both trucks on Flash Auto's chassis dyno in Albuquerque, New Mexico, to see how the real world power figures compare to Dodge's advertised numbers. As we were generating power numbers, the differences in emissions controls became immediately obvious. The 5.9L made plenty of smoke under load, even in stock form. By contrast, the 6.7L was squeaky clean during our dyno pulls. Advantage: 6.7L Cummins

Stock Power Numbers
The 5.9L-powered truck put down 269 hp at 2,550 rpm and 594 lb-ft of torque at 2,300 rpm; and the 6.7L-equipped Dodge put down 259 hp at 2,850 rpm and 487 lb-ft at 2,750 rpm. Runs were made in direct drive for both trucks-however it should be noted that the 5.9L Cummins was backed by the 48RE four-speed automatic transmission and the 6.7L used the new 68RE six-speed automatic. Unfortunately, the 5.9L Dodge used in our test had 35-inch Toyo tires on 20-inch Eagle Alloy rims. In order to limit the variables between the two trucks, the stock tires and wheels from the 6.7L truck were swapped onto the 5.9L truck, resulting in 10 additional peak hp and 10 lb-ft of torque. Advantage: 5.9L Cummins

Installing Performance Air Intakes
After getting stock power figures, we installed some typical aftermarket components on both trucks to see how they responded to the modifications. We began at the front of the trucks by installing S&B intakes (5.9L P/N 75-5033 and 6.7L P/N 75-5015). Both S&B air intake kits used large-diameter, smooth, molded tubes and multi-layer cotton gauze filters that meet ISO 5011 specifications. The only real difference between the intake kits for the different engines was the installation of a mass air flow (MAF) sensor to the intake on the 6.7L Cummins in addition to the air intake temperature (IAT)sensor used on both engines. The S&B intakes were designed to route cool air from the stock air duct in the fender, and included detailed instructions complete with color photos. Minor trimming was necessary to get the feet of the new airbox to fit in the locating grommets on both trucks, but this was a small price to pay for an intake that costs a fraction of other competitors' products and delivers just as much horsepower and superior filtration.Advantage: Tie