transamz9 wrote:
mich800 wrote:
blofgren wrote:
4x4ord wrote:
I looked at the numbers a little closer. If the Cummins averaged an rpm where it made 355 hp (that is about the average power that the Cummins produces throughout its rpm range), the Ram had to be 80% efficient at getting the engine's power to the pavement.
The average power that the Powerstroke makes between 1800 and 2800 rpm is 385 hp.
If the Ford was able to run at an rpm where it averaged 385 hp it would have been 72% effecient at putting its power to the pavement. 80/72 = 1.11. You'd expect the Ram to have gotten about 11% better fuel economy. It got 12.5 percent better fuel economy.
Edit: the average hp the Cummins makes from 1800 to 2800 is actually 352 Hp compared to the 355 I used above. That means the Ram could have been 81% efficient at putting its power to the pavement. 81/72=1.125 meaning you'd expect the Ram to get 12.5 % better fuel economy.
I find this very interesting.
Or could it be that the 6.7L Powerstroke simply doesn't put out the HP that Ford claims it does? It certainly is looking that way.
I would be more inclined to think it is either computer, transmission gear ratios, or overall drivetrain losses compared to the Ram. The drag race is a good indicator of peak HP but much more comes into play over a 10 minute plus test. So short term the Ford has shown it has higher HP. But over this test they both put down virtually identical average HP.
I actually think that the drag race just shows that Ford doesn't manage their torque as much as ram on the low end.
Yes they are both putting the same power to the pavement. No matter how you look at it some things don't quite add up:
The Ford could be holding gears much longer and running at low rpm (low hp) for long periods up the hill. If this is the case it is surprising that the Ram gets better fuel economy.
The Ford crankshaft power could be what Ford claims but then their driveline is very inefficient as compared to the Ram.
Ford could be lying about their horsepower but then it is surprising that it kicked butt in the drag race.
Bottom line is: as fantastic as the Powerstroke/TorqShift is, the Cummins/Aisin appears to be better.
Edit: There is one more possibility that makes sense. If the Ford spent a significant time at the high end of its rpm scale .... say 3000 rpm, where it could not quite make the jump from third to fourth. It was using 355 Hp but couldn't rev any higher nor quite make the jump from 3rd to 4th. Revving above peak HP it runs very inefficient. Although it may be rather unlikely that this scenario played out, this is one scenario that would explain everything. This spot in the gears is at about 45 mph.