You've seen how the 2010 Dodge Ram 3500, 2011 Ford F-350 Super Duty and 2011 GMC Sierra 3500 HD stack up to one another in our Heavy-Duty Truck Comparison Test. Now here's a look at how well each engine puts its stuff to the pavement -- rather, the drum -- as we recently spent some time on the dyno rollers with these trucks.
Diesel newbies will probably be puzzled by the low redlines found in these dyno charts. Yes, diesels rev low, owing in part to the fact that the diesel combustion process involves an elaborate courtship of the fuel and air in the combustion chambers. That, and diesels' high cylinder pressures require massive components, which in turn impose mechanical limitations on maximum speed.
Modern diesels employ ever-higher fuel delivery pressures and multiple injections per combustion event in order to improve fuel atomization, promote mixing and manage the resulting combustion process. These factors help to improve not only emissions and fuel consumption, but output benefits as well, something that is apparent by the impressive numbers generated by these trucks.
As usual, we strapped each truck to a Dynojet 248 inertial chassis dyno and performed as many runs as necessary to achieve a stabilized and repeatable result.
The GMC Sierra HD's 6.6-liter Duramax V8 threw down the biggest power number of the three diesels, turning the rollers to the tune of 360 horsepower. Torque, which peaked at 665 lb-ft, wasn't exactly thin, either. You'll notice this peak torque value occurs at some kind of tumor from the prevaling torque characteristic.
The GMC produced somewhat inconsistent results on the dyno, as its transmission insisted on downshifting when in manual mode. It took a bit of coercion and a lot of runs on the dyno to get the big white pickup to turn the rollers in an agreeable way.
This kind of grunt is impressive in a box-stock truck. Sure, you can buy aftermarket controllers to extract silly numbers that would eclipse those of the trucks in this test. The tradeoff with those black boxes is that you run the risk of extremely high exhaust gas temperatures which translate into long-term durability that can only be described as a giant question mark.
Of all three trucks here, the Ford's 6.7-liter Powerstroke V8 powertrain was by far the most cooperative on the dyno. Its transmission stays on task, resolutely staying in the gear of your choosing when in manual mode. After all, sometimes you just want that extra bit of control over the powertrain, and what would be the point of manual mode if the transmission grows neurons and decides it knows better than you?
The Ford's friendly transmission allowed its dyno pulls to begin from very low in the rev range, unlike the other trucks that would downshift of their own accord. We saw dead-consistent results from the Ford, too, which ground out 333 horsepower and a test-topping 690 lb-ft of torque to the rollers.
Although the GMC ekes out the most power in this comparison, it does so only briefy -- the Ford has the edge for the brunt of the rev range (see overlay of dyno data from each truck below). Torque is quite flat from 1850 to 2650 rpm, which is a substantial fraction of the engine's total rev capability.
In a way, it's remarkable that the Dodge's 280 horsepower and 559 lb-ft of torque as measured by the Dynojet chassis dyno were the meekest results in the test. Just a few years ago this kind of sauce would have been unheard of in a production diesel pickup.
The Dodge has neither the peak output nor the broad shoulders of the other two. Similar to the GMC, the Dodge's transmission takes matters into into its own hands when it decides there are too few revs on the tach.
Powered by a substantially overhauled 6.7-liter Cummins inline-six, the Dodge sports the eldest engine in the bunch. Ford's Powerstroke is all-new this year, and GMC's Duramax was new in 2010 and, unlike the Dodge, both employ urea as their exhaust aftertreatment strategy.
Without urea, the Dodge's engine requires more exhaust gas recirculation to tamp down NOx emissions, which is one explanation as to why its output lags the others.