Downshift or exhaust brake?

4x4ord wrote:
I think people are a little deceived with regard to the performance of these exhaust brakes. When you calculate the braking effect that increased back pressure makes on an engine's total braking capability it is not as big of number as what many likely think. I calculated that the exhaust brake on my Ford could potentially add about 75 negative horsepower to the engine's braking ability. Someone with a stop watch and a buddy should rev their truck up to 3500 rpm in 3rd gear and time how long it takes for the engine rpm to drop from 3000 rpm to 2500 rpm with the exhaust brake on vs with it off. I'm betting the exhaust brake will shorten the time fairly significantly but Me Again will definitely be surprised at the result if he thinks a truck free wheels without an exhaust brake turned on and can lock the wheels up with it turned on. Pumping air takes power.... and it takes a more power with higher back pressure but two facts have to be kept in mind when you think about an exhaust brakes potential: 1st... there is a limit to how much back pressure an exhaust brake can generate before the exhaust valves start floating; 2nd... when an engine is revved to 3000 rpm it is going to be creating back pressure even without the exhaust brake turned on. So again if someone were to perform the above test on level ground the difference will be significant but not overwhelming.