Gas Versus Diesel Comparison By Brand - 15% Grade with Trailer
This page is an opportunity to compare the relative performance of the single rear wheel gas pickups against their dual rear wheel diesel counterparts on the 15% grade.
Obviously, not an apples to apples comparison (primarily because of weight and rear axle and rear track differences between the 3/4-ton and 1-tons), but it provides some indication of the scenarios where each type of engine excels.
If you've been examining the earlier pages where we compared the relative performance of the diesel and the gas trucks, you'll see this page is totally different from the quarter-mile and 7% grade tests. Engine relationships varied markedly from manufacturer to manufacturer tackling a 15% grade.
All the diesels got the jump on their gas counterparts, but diesel performance started to level out from the middle of the run. As the oil burners' velocities went steady state, the Ford and GM gassers' speed curves gained altitude all the way to the end, and did, or would, beat the diesels on this hill, while Dodge's diesel and gas speed curves stayed parallel to each other from start to finish.
Looks like these results support the old adage that diesels are for torque and gassers are for horsepower.
The Dodge trucks show how the 5-speed transmission struggled to support the HEMI, whereas the 6-speed enabled Cummins ran a very strong run.
Ford's F-250 and F-350 finally developed some unique performance patterns, even though they are using the same 5-speed TorqueShift transmission. But look at how well the V10 was running at the 250-meter finish line versus the V8 Power Stroke. Again the gasser was traveling faster than the compression ignition motor. The F-350's speedo barely inched up from 100-m to 250-m, while the F-250 gained over 6-mph.
The 6L90 transmission is very well paired to the power band in the GMC Sierra's Vortec Max V8, but that powertrain's got nothing on the much stronger Allison/Duramax team. Check out the difference in time between the two GMT900 pickups.
What would really make for an interesting contest is if we saw two-speed rear axles return as an option on the gas pickups, like two-ton farm trucks of the seventies had. You could develop torque like a diesel using a low axle ratio, say 4.30, but flip a switch on the two-speed diff to a 3.55 to get 20-mpg when not towing.