One-Ton Diesel Pickups - 15% Grade with 10,500# Trailer:
After witnessing the dramatic results of the 15% contest among the gas trucks, we were even more interested to see what changes or stumbles might await the diesels on this steep hill.
| The Results: |
| Time (seconds) |
| Distance (Feet) | 2007 Dodge Ram 2500 Quad Cab 4x4 3.73 Rear Axle | 2008 Ford F-250 Super Duty Crew Cab 4x4 4.30 Rear Axle | 2007 GMC Sierra 2500 Crew Cab 4x4 3.73 Rear Axle |
| 164 | 8.66 | 9.2 | 8.64 |
| 328 | 13.49 | 14.03 | 13.07 |
| 492 | 17.95 | 18.39 | 16.98 |
| 656 | 22.3 | 22.59 | 20.69 |
| 820 | 26.55 | 26.75 | 24.28 |
| Speed (miles per hour) |
| Distance (Feet) | 2007 Dodge Ram 2500 Quad Cab 4x4 3.73 Rear Axle | 2008 Ford F-250 Super Duty Crew Cab 4x4 4.30 Rear Axle | 2007 GMC Sierra 2500 Crew Cab 4x4 3.73 Rear Axle |
| 164 | 20.98 | 20.73 | 22.87 |
| 328 | 24.84 | 24.85 | 27.43 |
| 492 | 25.39 | 25.64 | 29.79 |
| 656 | 25.96 | 26.22 | 30.79 |
| 820 | 26.79 | 26.43 | 31.97 |
15% Grade Cumulative Time...
15% Grade Cumulative Time Over 250-Meters 1-Tons With 10500# Trailer
15% Grade Cumulative Speed...
15% Grade Cumulative Speed Over 450-Meters 1-Tons With 10500# Trailer
| 15% Grade Cumulative Time Over 250-Meters 1-Tons With 10500# Trailer | 15% Grade Cumulative Speed Over 450-Meters 1-Tons With 10500# Trailer |
If we were directing marketing for GM, here's how we'd pitch its diesel motor. D for Duramax. D for dominant. Check out the how fast the Chevy finished the hill climb - more than 5-mph faster and over 2 seconds quicker than either the Ford or Dodge haulers! This time it even beat the Cummins in the first 50-meters.
Though the Power Stroke was still slower than the Cummins to the top, the gap between those two engines narrowed substantially on the 15% grade, in favor of the Ford. If the F-350 and Ram 3500 both had 3.73 rear gear ratios, instead of the Ram's 4.10, we think the F-350 almost certainly would have moved into the second spot.
But there was an incredibly interesting reason why the performance gap between the F-350 and Ram 3500 seemed to close so much. After two sprints up the hill, the F-350's diesel particulate filter (DPF) went into regeneration mode. The DPF is a new emissions control device required to reduce diesel particulate emissions 10-fold from 2006 model year levels. Regeneration is triggered when the truck senses too much back pressure from the DPF, because of a large amount of trapped particulates. To get rid of the soot, the engine injects metered amounts of diesel fuel into the exhaust stream to incinerate the soot in the filter. On the third run, after regenerating, the F-350 ran the hill up to a full 2-kilometers-per-hour (1.2-miles-per-hour) faster than its first two passes.
We were very surprised by the apparent power boost the Power Stroke received from regeneration. It illustrated just how much the new DPFs can restrict airflow through the exhaust system, and the challenge faced by all the OEMs to improve engine performance while complying with new emissions regulations.