Downshift or exhaust brake?

Me Again wrote:

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.

No I will not be!!! I do not believe you have a RAM/Cummins and do not know what you are talking about.

Just to put some numbers on my claims I'm saying that a Ram 3500 will have about 120 negative horsepower acting on it when the throttle is backed off while the engine is spinning 3000 rpm without the use of the exhaust brake. (this includes all the forces acting on the truck to try to slow it down from 55 mph such as wind resistance and rolling resistance and the power required to spin the entire powertrain around.) Flip the engine brake on and you will gain maybe another 60 negative horsepower. Those numbers are not going to be far off. Someone with a Ram who knows the weight of his truck could rev his truck to 3500 rpm in 3rd gear then back off the throttle and using a stop watch measure the time it takes for the engine to slow from 3200 rpm to 2700 on level ground with the exhaust brake on and then measure again with the exhaust brake off. The negative horsepower produced by the exhaust brake could be calculated from that information.