We already know that Ford’s all-new 6.7-liter Power Stroke V-8 diesel is rated at 390 horsepower (at 2,800 rpm) and 735 pounds-feet of torque (at 1,600 rpm) and GM’s updated 6.6 Duramax V-8 diesel is rated at 397 hp (at 3,000 rpm) and 765 pounds-feet, but those numbers don’t tell the whole story.
The true measure of diesel performance is how well its muscle is managed over the engine’s power band. How soon is peak torque available and for how long? The broader the torque curve is and the sooner peak torque hits, the better.
For the first time, we’re presenting the horsepower and torque curves for both the 2011 Power Stroke and 2011 Duramax engines. The data is courtesy of Ford and General Motors with the disclaimer that both power curves were delivered as rendered image files and not as tabular data, which would have allowed us to recreate the graphics independently.
The individual curves are presented first but we’ve taken both graphs and combined them into a single chart, so you can see where the differences are across engine speeds.
2011 6.7-liter Power Stroke V-8 Power Curves (courtesy of Ford)
2011 6.6-liter LML Duramax V-8 vs. 2010 6.6-liter LMM Duramax V-8 Power Curves (courtesy of GM)
The Comparison: 2011 6.7-liter Power Stroke V-8 vs. 2011 6.6-liter Duramax V-8
Here’s what we think is interesting:
- Torque: The Power Stroke puts out more torque than the Duramax until about 1,350 rpm, at which point the Duramax rapidly spikes towards its best-in-class peak torque at 1,600 rpm. After that point, the two motors appear to even up again around 2,450 rpm before the PSD drops below 700 lbs-ft around 2,700 rpm. The Duramax maintains a wider torque band that remains north of the PSD until 3,000 rpm, at which point rapidly tails off and both engines overlap again around 3,300 rpm. In general, the Duramax has a taller, broader torque band than the PSD.
- Horsepower: The Power Stroke appears to maintain higher horsepower than the Duramax throughout most of the rpm range but the Duramax is able to keep the power coming a bit longer and outguns the PSD at about 2,900 rpm before it rapidly tails off and again falls below the PSD around 3,300 rpm.
Part of Ford's apparent horsepower advantage may be the rendering of Ford's power curve. When we calculate horsepower using the formula HP = (rpm x torque)/5252 we come up with a rating of 223 hp for the Power Stroke and 233 hp for the Duramax at 1,600 rpm -- the claimed peak torque point for both motors. The graph overlay should show the Duramax slightly higher than the PSD at this point but it doesn't.
It will be interesting to see how horsepower differences impact acceleration times when the trucks are empty and pulling heavy trailers during our upcoming HD Shootout.
One thing the comparison chart can’t tell us -- until we put the trucks head-to-head -- is how well their power is managed by their six-speed automatic transmissions. With ratings as close as these, transmission logic is going to be critical for differentiating which rig performs better. The chart also doesn’t account for weight differences. The Ford Super has traditionally been the heaviest pickup in the segment. We also wonder how much of a role controlling emissions is playing in changing some of the inflection points of the curves.
We’re looking forward to testing both new engines on a chassis dyno ourselves, so we can see the power and torque curves calculated outside of Ford’s and GM’s powertrain labs.