Photos courtesy of Diesel Power, General Motors
Over the summer, we published the results of our nine-truck Heavy-Duty Shootout, where we selected the Chevy Silverado 2500 HD and GMC Sierra Denali 3500 HD as our two top picks in the three-quarter-ton and one-ton diesel categories. But our readers raised two important points.
The first point was that we didn't test Ford’s "Job 2" engine calibrations for the all-new 6.7-liter Power Stroke V-8. The free powertrain software update for 2011 diesel Super Dutys boosts the ratings from 390 horsepower and 735 pounds-feet of torque to an astonishing 400 hp and 800 pounds-feet, eclipsing GM’s 6.6-liter Duramax V-8 rating of 397 hp and 765 pounds-feet. We didn't test the re-rated Ford trucks because they weren’t available at test time.
The second concern was about the quarter-mile and hill-climb acceleration tests, where we measured performance over relatively short distances pulling 10,000-pound and 12,000-pound trailers. The tests were enough to provide consistent evidence of the strength of GM’s powertrain, but some thought Ford’s diesel and new six-speed would have beaten the Chevy and GMC if the distances were greater.
We didn't disagree with these two points and wondered about both ourselves, even though we know our Shootout comparison tests are the most rigorous exams you’ll find to judge pickup truck capability.
Then, in late September, Chevrolet challenged Ford to a real-world showdown in the Colorado Rockies, similar to the Mike Rowe head-to-head towing competitions that Ford has used to promote the capabilities of its F-Series pickups. Ford declined, but the bowtie boys decided to press forward and invited PickupTrucks.com and Diesel Power magazine to witness the test.
We agreed with a few conditions: Chevrolet had to use test trucks purchased off the lot from Chevy and Ford dealers and the Super Duty had to have the 400/800 power ratings. They couldn't come from GM's captive test fleet and the trucks had to be as "apples-to-apples" as possible when it came to features and equipment. While Chevrolet originally wanted to test three-quarter-ton HD pickups — the heart of the HD market — we had to use one-ton trucks because that was the only way to match equivalent rear axle ratios of 3.73. We also had to drive and instrument the trucks to measure the results ourselves. Chevy reps would be along for the ride.
Chevrolet met those conditions, and we picked up two brand-new dealer-bought HD pickups in Detroit. The 2011 Chevrolet Silverado 3500 LT four-wheel-drive crew cab came from Mike Savoie Chevrolet in Troy, Mich., with 8 miles on the odometer and 0.9 hours on the engine meter. The "Job 2" 2011 Ford F-350 Super Duty XLT four-wheel-drive crew cab was sold at Harold Zeigler Ford Lincoln in Elkhart, Ind., and driven to Detroit by a third-party fleet service. Two Diesel Power staffers drove the trucks 1,250 miles to Denver.
How equivalent were the trucks? They were probably the most evenly matched HD pickups we've tested. Besides the same rear axle ratios, the $54,805 8,440-pound Ford was just $65 and 220 pounds more than the $54,740 8,220-pound Silverado. Both lacked fancy equipment such as leather seats, navigation systems and sunroofs.
The location and the load
We knew we needed a real-world place to test both trucks, so we chose the eastbound ascent from Dillon, Colo., to the top of Eisenhower Pass on Interstate 70. It’s perhaps the toughest stretch of road a loaded truck will encounter on a major cross-country highway – call it the Nürburgring of pickup trucks because nearly every bit of towing and braking hardware is stressed to its max for multiple miles at a very high altitude.
The grade starts at about 5 percent for two miles and increases to about 7 percent for the remaining six miles, to the entrance to the Eisenhower Tunnel, the highest vehicular tunnel in the U.S. Despite that lofty elevation, an average of more than 30,000 vehicles crossed in both directions each day last year, according to the Colorado Department of Transportation.
We also needed a heavy trailer that the trucks could share. Chevy lined up a 6,500-pound gooseneck with three 4,140-pound pallets of flagstone lashed to the flat bed for a grand total of 18,920 pounds. That brought the gross combined weight rating for the Chevy to 27,140 pounds before four adult males jumped in and added another 800 pounds, for a grand total of 27,940 pounds, or 96 percent of the Silverado’s maximum GCWR. The total for the Ford F-350 was 28,160 pounds, or 94 percent of the Super Duty’s maximum GCWR.
For our test, we used a stretch of I-70 that started in Dillon at 8,776 feet and ended at exactly 11,000 feet, rising 2,224 feet over 7.6-miles (approximately 40,000 feet).
But we didn’t just time the trucks up the grade. We also evaluated their exhaust-brake performance while heading the opposite direction back to Dillon with the nearly 19,000-pound trailer pushing these monster HDs downhill. An exhaust brake saves on brake and transmission wear by clamping down the engine’s turbo vanes, creating back pressure to engine brake the truck. It also reduces the potential for brake fade during long descents, increasing downhill safety while towing and overall wheel brake life.
If you were wondering where the Ram 3500 is in all of this, it wasn't included because these weights exceeded its 24,500 maximum GCWR by more than 2,500 pounds. It wouldn’t have been safe or responsible to test the truck in these conditions.
To help manage these astonishing weights, which we couldn’t have imagined a decade ago, we used a professional driver with a commercial driver’s license paid for by Diesel Power Magazine. Please see Diesel Power for the driver's bio.
Each truck was run up the grade in Tow/Haul mode starting in four-wheel drive for max traction in the cold conditions and switching to two-wheel drive at approximately 30 mph. The fastest time was used for the comparison.
We ran the Ford four times. The first two runs were with only three adult males to offset the Chevy’s 220-pound curb weight advantage, and the last two runs had all four of us in the trucks. The fourth run was Ford’s fastest time. Two-hundred-twenty pounds doesn’t matter much when you’re pushing almost 15 tons against gravity.
Temperatures ranged from 5 degrees to 18 degrees, according to the trucks’ outdoor temperature readouts. It was so cold that neither truck’s fan turned on, though the next day, at just 35 degrees, both trucks’ fans turned on frequently to cool the engines.
The trucks were at a dead stop before each run. The driver ran wide-open throttle from start to finish. We didn’t encounter any traffic on the road during the late-night climbs.
We used our own GPS-based Racelogic VBOX test kit to record performance and geographic data.
The Ford F-350's best time up the grade was 10 minutes, 46.8 seconds at an average speed of 42.41 mph. The top speed was 58.5 mph, and it happened just before the point where the grade increased from 5 percent to 7 percent.
This chart shows each truck's speed climbing the 7.6-mile grade against the clock. The Silverado reached 11,000 feet in 518.2 seconds and the Ford finished in 646.8 seconds.
This chart shows the speeds of both trucks relative to each other over the 40,000 foot (7.6 mile) run to 11,000 feet in elevation. Note how similar the speed patterns are for each truck as the grade changes throughout the climb.
The Chevy Silverado was significantly faster. It finished more than two minutes ahead of the F-350, in 8 minutes, 38.2 seconds. Average speed cruising up to 11,000 feet was 53.63 mph, 11.22 mph faster on average than the Ford. The Chevy’s top speed was 67.38 mph for a few seconds before the grade changed from 5 percent to 7 percent.
The Chevy and Ford had similar performances at the start of their runs. The Ford clicked off the quarter-mile in 31.25 seconds at 45.13 mph, and the Chevy ran the same distance in 28.93 seconds at 50.3 mph. But the Chevy was already coming on like a freight train at that point. It took the Silverado 28.56 seconds to go from zero to 50 mph, while it took the Ford 42.02 seconds.
Both trucks ran the first part of the grade in 4th gear and dropped down to 3rd gear for the rest of the climb.
Exhaust brake test
For the exhaust brake test, we exited Eisenhower Tunnel westbound and set both trucks’ speed to 55 mph in 4th gear. The Silverado has a push-button-activated exhaust brake that can work in or out of Tow/Haul mode, while the Ford’s exhaust brake is automatically enabled when the truck is in Tow/Haul. Unlike the Duramax, the Ford’s exhaust brake can't be turned off by the driver.
We wanted to see which truck required the least amount of wheel brake application, so when speeds reached 60 mph, the driver applied his left foot to the brake to slow down the truck to 52 mph to start the cycle again.
The difference in exhaust brake performance (echoing the much shorter test performed in the HD Shootout) was starker than the difference towing up the hill.
After four runs in the Ford, we had to manually slow the truck between 11 to 14 times during each descent to keep it from exceeding 60 mph. Ford’s exhaust brake seemed to have minimal effect slowing the rig and keeping our driver from getting that “white knuckle” feeling you don’t want to have when your 15-ton rig is rolling down a hill. Ford’s six-speed transmission did a nice job downshifting from 4th to 3rd gear after the foot brake was applied to help slow things down.
The Chevy was a superhero on the descent. It was like Superman digging his feet into the pavement to stop a runaway locomotive. In three downhill runs, we averaged one to two manual brake applies. That’s it. It consistently hung in at a steady 58 to 59 mph and stayed at that speed for miles. When we applied the foot brake after the first time, the Chevy downshifted from 4th to 2nd gear near redline at 52 mph and kept shedding speed until we tipped into the throttle to get back into 3rd and started picking up speed again. We never shifted down to 2nd gear in the Super Duty, slowing the truck to 52 mph.
At the turnaround point in Dillon to start each test cycle, the most telling aspect of our exhaust brake test was the strong smell of hard-worked brakes in the Ford and the absence of that smell in the Chevy. That doesn't just save on brake wear. It saves on frayed nerves as well.
In short, the Chevy Silverado's performance surprised everyone, given Ford's higher stated power figures for the 6.7-liter Power Stroke. Finishing two minutes ahead of the Super Duty over a 7.6-mile grade at more than 90 percent GCWR is nothing short of a dominant showing for Chevy. The exhaust brake performance is perhaps even more telling and welcome news for frequent heavy towers.
What accounts for the significant performance differences between the Chevy and the Ford in this comparison? We originally thought it might be a gap in the Power Stroke's high altitude engine calibrations, which optimize combustion performance based on driving conditions, but now we think its part of the nature of the 6.7's unique single sequential turbo.
Ford's turbo features a single turbine and two compressors placed back-to-back. It's possible that Ford's siamese compressor design is losing some efficiency the higher it climbs.
For braking, both trucks depend on variable geometry fins that surround the turbine. They clamp down to restrict exhaust flow and create back pressure in the engine to slow the truck down. The Duramax appears to be able to clamp down more strongly than the Power Stroke.
Interestingly, Honeywell subsidiary Garrett is the same turbo supplier for both diesel engines.
Regardless of the cause of the performance gap between these two incredibly capable HD pickups, we reaffirm the results of our 2010 HD Shootout in the real world. There’s no question that GM's latest diesel pickups are the performance leaders in the class. Chevy doesn't just run deep. It runs high as well.
For more information and a second take on this test, be sure to check out Diesel Power.
All of the data we collected during the Rumble in the Rockies has been provided to Ford and General Motors for their review. PickupTrucks.com and Diesel Power Magazine paid for our own travel and lodging expenses associated with this test. We were not compensated for any part of our participation by GM.