Downshift or exhaust brake?

4x4ord wrote:
I took my Ford out this morning and conducted a test that I think demonstrates the effectiveness of an exhaust brake.

On a level stretch of highway I revved the truck to 3500 rpm in 3rd gear before backing off on the accelerator. I watched the speedometer as the truck started to slow down and with the exhaust brake off I timed how long it took for the truck to slow from 100 kph to 80 kph. I then followed the same procedure with the exhaust brake on. Then I timed how long it took for the truck to slow from 100 to 80 kph with the transmission in neutral. After recording the results I found an online calculator that allowed me to calculate the negative horsepower acting on the truck in each of the three cases. Here are the results:

Exhaust brake off ............. 5.25 seconds ...... negative 142 horsepower
Exhaust brake on ............. 3.98 seconds ...... negative 187 horsepower
Transmission in neutral .... 16.5 seconds ...... negative 45 horsepower

So the results demonstrate that on my Ford turning the exhaust brake on gives about 45 additional braking HP over transmission braking alone with the engine revved in the range of 3200 to 2600 rpm. I agree with Me Again in that you can feel the difference. To use the full potential of the exhaust brake my truck would have to be revved to 4000 rpm.

Here is a link to the online calculator: click