Downshift or exhaust brake?
I was just thinking after reading a post about gas vs diesel trucks where somebody mentioned they liked diesel because of the exhaust brake. I've never had a diesel, always gas. If I come up to a long...
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rhagfo wrote:Cummins12V98 wrote:Me Again wrote:Cummins12V98 wrote:
Going down at 3k it will take a bit of throttle to show boost but I will give it a shot.
I think it was be very hard for a truck going down a hill to create much boost, forget the exhaust brake. Boost is created when the truck is WORKING! Going to be very hard to work it very hard going down a hill.
EXACTLY, that is why I said "Going down at 3k it will take a bit of throttle to show boost"
I still think not possible.
To create Boost requires load and throttle, once you apply any throttle EB disengages. So you can’t have throttle, load and Exhaust Brake at the same time!
That is my story and I am sticking to it!
rhagfo wrote:Cummins12V98 wrote:Me Again wrote:Cummins12V98 wrote:
Going down at 3k it will take a bit of throttle to show boost but I will give it a shot.
I think it was be very hard for a truck going down a hill to create much boost, forget the exhaust brake. Boost is created when the truck is WORKING! Going to be very hard to work it very hard going down a hill.
EXACTLY, that is why I said "Going down at 3k it will take a bit of throttle to show boost"
I still think not possible.
To create Boost requires load and throttle, once you apply any throttle EB disengages. So you can’t have throttle, load and Exhaust Brake at the same time!
That is my story and I am sticking to it!
The formula for calculating the horsepower required to pump a liquid at pressure is: flow (gpm) x pressure (psi) / 1714. A very similar formula can be used to calculate the power required to pump air at pressure.
When talking about an exhaust brake on a pick up truck it is a little bit of a grey area to think of the engine brake as being on or off. Basically the diesel engines in our pick ups can be thought of as air pumps. When the throttle is backed off and the trailer is trying to push our truck down the grade our engine is acting as an engine brake even without an exhaust brake installed or turned on. It takes power to push air through and out the engine. If we down shift we speed the engine up thereby increasing the amount of air being pushed through the engine as well as increasing the pressure that the air is being pumped through at. Both these factors (air flow and pressure) contribute to an increased level of braking. If we restrict the exhaust so that the air is being forced out of the engine at a higher pressure we increase the power required to push the volume of air through the engine which increases the braking effect. If we utilize the turbo's ability to super charge the air intake we are forcing more air through the engine and past the turbo. This higher volume of air going through the engine raises the back pressure causing more braking and more boost so there is a compounding effect going on when the turbo is used as an exhaust brake. I believe, the exhaust brake switch on the dash of the new trucks causes the vane angle on the exhaust turbine to become more aggressive which restricts the air flow, spins the turbo faster and creates more boost (higher airflow) which leads to more back pressure and a higher level of engine braking.
