What happens when the performance of your newly-developed vehicle exceeds the capabilities of the test equipment used to measure it? Ford Truck engineers faced that dilemma while preparing for the SAE J2807 towing tests of the all-new 2017 F-Series Super Duty.
Their conclusion: "We need a new dyno."
The SAE J-standard, “Performance Requirements for Determining Tow-Vehicle Gross Combination Weight Rating and Trailer Weight Rating” (http://standards.sae.org/j2807_201602/) replicates how a laden vehicle climbs the infamous Davis Dam grade—a daunting 11.4-mi (18.3-km) section of Arizona State Road 68 near the Colorado River. That long, tortuous pull starts at sea level and climbs to above 3000 ft, and its maximum 7% grade—a seven-foot incline per every 100 ft of linear distance—is renowned among automotive test teams for overtaxing cooling systems, frying brakes, and separating the champs from the chumps in terms of towing and hauling capability.
During development of the 2017 F-250/350, Ford engineers recognized that the increased torque of the 6.7-L diesel V8, expected to exceed 900 lb·ft (1220 N·m) and top that of the 2016 Ram’s Cummins diesel (Ford has yet to release its SAE-certified power and torque ratings), along with the new truck’s significantly stiffened chassis, would outpace the capability of their existing dyno sleds.
This is no real surprise, given the steady escalation of American diesel pickup muscle. Consider that Ford’s first 6.9-L diesel V8 (Navistar-built) entered the fray in 1982 with 170 hp (127 kW) and 315 lb·ft (430 N·m). The 2016 Super Duty’s 6.7-L V8 delivers 440 hp (328 kW) and 860 lb·ft (1166 N·m)—output that not long ago would've qualified for Class-8 truck duty.
“In more than 25 years of doing this [tow testing] work, we used the same dyno, which did the job,” explained Jim Sumner, Ford product development engineer. “But the new truck is so powerful we needed new equipment to test out its capability.” The upgraded towing dynamometer is in service at Ford’s Arizona Proving Grounds, allowing engineers to simulate the actual Davis Dam road testing (as well as testing on other U.S. mountain highways).
Engineers upload digitized map topography to the dyno sled, which adjusts to the correct grade. The sled employs an electric brake limiter to provide drawbar “pull” against the vehicle, simulating a climb even while on level ground.
Designed and supplied by Milwaukee-based Taylor Dynamometer (http://www.taylordyno.com/), the RSL-25K dyno sled acquired by Ford is capable of a maximum drawbar pull of 5620 lb (2549 kg)– a 181% increase compared with the 2000 lb (907 kg) from Ford’s previous dyno. This enabled simulation of steeper hills, Sumner noted. He said a common simulated grade used for testing is approximately 7%, to replicate the Davis Dam run, but the new towing dynamometer used at Ford’s Arizona Proving Grounds can simulate up to a 30% grade.
The SAE J2807 standard includes acceleration, climbing, launching, and vehicle weight parameters. Vehicles with a gross vehicle weight rating (GVWR) less than 8500 lb (3855 kg) must carry a 150-lb (68 kg) driver and a 150-lb passenger. Vehicles heavier than 8500 lb add an extra 100 lb of equipment.
For a given trailer weight, J2807 compliance means the tow vehicle must accelerate to 30 mph in under 12 s, and accelerate to 60 mph in under 30 s. Roll-on acceleration 40 to 60 mph on a level surface must be accomplished in under 18 s. Vehicles with dual rear wheels are permitted extra time to complete this test. For the climb test that replicates Davis Dam, tow vehicles must sustain a minimum 40 mph with their A/C on its highest setting. “Duallies” again have a lesser (35 mph) minimum-speed bogie.
The J2807 launch test replicates a 12% grade, and requires the tow vehicle to move 16 ft (4.9 m) uphill, from a standstill, five times within five minutes in both forward and reverse.
Expect GM, FCA, and possibly Nissan to follow suit and upgrade to more-capable testing equipment—good news for Taylor and other dyno makers—as the industry battle for heavy-duty pickup hauling and towing bragging rights shows no sign of abatement.