The Big Three's New Diesels put on a Dyno

Turtle n Peeps wrote:

4x4ord wrote:
One truck can put 10,000 lb ft of torque to the rear axle and a second truck can put 20,000 lb ft of torque to its rear axle...Who is faster up the hill? There is no way of even guessing without knowing the rpm (or power). Now if we know the first truck has a 400 hp engine and the second truck only 200 we can have a high level of confidence that the 400 hp truck wins.

Someone gets it for once on this site!

Someone please make this post a sticky at the top and make it mandatory to read it before they can sign up! :B

While that is generally true, it is not true all the time. It is not about how much power an engine makes at peak. It is about how much power the engine/truck makes at the rpm and gear that the torque limits it to. Horsepower is derived from rpm and torque so if the vehicle does not have enough torque to over come the load at the rpm it makes peak horsepower, then it is making less than peak power.

If the 400 hp vehicle is only limited to a an rpm where it is making less then half its power, then the 200 hp engine will win if it has enough torque to pull the load at peak power. Gears also limit speed. If you do not have enough torque to pull a hill in 4th and you loose speed in that gear, then the vehicle will be limited to 3rd which will also limit its speed regardless if it has more horsepower or not.

Then there is the factor of power loss due to altitude with N/A engines and FI engines where the lower powered FI engine will blow the doors of the higher powered N/A engine. Even two FI engine turbochargers may act differently at elevation with one having a more efficient blade and bearing allowing for higher turbo rpms to greater compensate for the pressure loss. We have seen this many times on the Ike.

There is also the factor of how each manufacturer is attaining that power numbers. If they each use one of the three different SAE standards to achieve their power numbers with one standard generally giving a higher number than the other standard, then engine with the higher power rating may not actually have more power. It may actually have less or the same power if they both used the same standard, but due to the standard they use it shows more power.