Downshift or exhaust brake?

4x4ord wrote:
Edit: I did a redo on this experiment. The first time I conducted this test I went out early in the morning while the truck had not yet warmed up. Tonight with the truck thoroughly warmed up the time to decelerate from 100 to 80 without the use of the exhaust brake was 7.3 seconds as opposed to 5.25 seconds. I wonder if when truck was cold the turbo could have been partially restricted to aid in warming the engine? This time testing I conducted the test over several times. With the exhaust brake on the time to slow down was very consistent. With it off there was much more variation. 7.3 was pretty typical and once it slowed down in 5.8 seconds. Anyway 7.3 seconds means 102 negative horsepower without the exhaust brake on.

So the more accurate data is:

Transmission in neutral..... 16.5 seconds .... 45 negative hp.

Exhaust brake off ..... 7.3 seconds ...... negative 102 hp

Exhaust brake on ..... 4.0 seconds ...... 186 negative hp.

So the exhaust brake created 84 additional reversing hp over gearing down alone. This is more inline with what I think most people would have expected. My prediction done prior to running the test was that the exhaust brake could create an additional 75 negative hp so I was in the ball park. My error was that I assumed a little more back pressure with the exhaust brake off then what there evidently is. Next week I might get to try the Jake brake out on our Kenworth.