Power Pullers --The Ultimate Tow Test: Part Three

One-Ton Diesel Pickups - 7% Grade With 10,500# Trailer
The same test approach and distance used for the three-quarter-ton gassers was used to grade the performance of the one-ton diesel pickups.

The final numbers speak clearly when it comes to which diesel powertrain performed best during the 7% hill climb, but watching it play out in the time and speed numbers is like witnessing a chess match. The best individual powertrain components and gear ratios can't win unless they all work together seamlessly and strategically.

7% Grade Cumulative Time Over... 

   

  read full caption

7% Grade Cumulative Time Over 450-Meters 1-Tons With 10500# Trailer

7% Grade Cumulative Speed... 

   

  read full caption

7% Grade Cumulative Speed Over 450-Meters 1-Tons With 10500# Trailer

The Ram 3500 took the early lead in the first 50-meters, with its torquey I6 (earliest torque peak out of the three trucks) and 4.10 final drive ratio. But by the time all the trucks gained some momentum shifting into second and third gears, the Silverado 3500's slightly higher power and torque figures - from the Duramax / Allison combo - were transferred to the pavement more efficiently through its 3.73 rear axle. When both trucks shifted into fourth gear, near the top of the hill, the Ram's speed curve flattened out while the Silverado's continued its upward trajectory.

Most surprising, though, was the Power Stroke's performance in the Ford F-350. Out of the box this truck weighed about 1,000-pounds more than the Dodge or Chevy rigs. Still, we were expecting better off-the-line performance assistance from PSD's dual sequential turbos, which work at both low and high speeds to provide up to a combined 42-psi of boost (versus 20-psi in the uni-turbo Duramax).

In comparison, the variable geometry turbo (VGT) setup in the Ram's Cummins diesel is also meant to provide low and high speed power throughout the RPM range, but instead of using compound spinners like the Power Stroke, it relies on a single turbo paired with a compressor sleeve that slides forward and backwards axially along the turbo shaft to variably change air volume and psi-boost to the engine. The same sleeve is also used to engage the Ram's exhaust brake. It's an elegant solution that tackles two different tasks.

The Silverado's Duramax variable vane turbo system is downright simple compared to the Ford and Dodge. Its one-piece exhaust turbine relies on a solid shaft to handle the stress of spinning at 120,000-rpm to suck in huge volumes of air as needed.

We think Ford may not be getting quite the bang for the buck out of its dual-turbos that Dodge and GM are getting from their air-compression architectures.

Another area needing a good tweak is the F-350's 5-speed transmission. Its gears don't grow fast enough to leverage the full power and capability of the Power Stroke. Occasionally the stars aligned for the Ford to fully loose the power housed in the PSD. Fourth gear is 1.00:1 on all the trucks, and this was where the Ford made the biggest jump in speed relative to the Dodge and Chevy - gaining more than 1.5-mph in the last 50-m.

The end result was the Silverado completed its run almost 5-mph (greater than 10%) faster than the F-350 and almost 2.5-mph quicker than the Ram. Wow!

The Duramax lives for climbing hills under load. We'd feel very comfortable calling on its power if we needed to pass slower moving traffic up a long, steep grade.