Downshift or exhaust brake?

4x4ord wrote:

ShinerBock wrote:

4x4ord wrote:


I don't know why both gauges don't read at the same time on your Ram. Maybe the gauges are set up to either show boost or braking depending on throttle position but never both? I know the boost gauge rises very significantly when I use the Jake Brake on my Peterbilt. The harder it works the higher the boost goes. In the case of these small diesels that use the vanes on the exhaust turbine to create back pressure I think the turbo is going to be set as aggressive as possible when its creating maximum braking..... at that point it should be making boost. I think the boost guage rises on my little Ford but I haven't used it much for towing yet. I'll pay more attention this summer.

But your Jake brake is an engine brake that utilizes the opening of exhaust valve during the compression stroke alowing that air to speed up your turbine and his exhaust brake utilizes a sliding nozzle to block exhaust going to the turbine.

I've never seen the exhaust brake on the newer diesels nor do I know how they work but it would make sense to utilize the turbo turbine to restrict the flow of exhaust and increase the boost pressure. Like I said earlier the boost pressure rises dramatically during engine braking on my Peterbilt. Again without knowing anything about the design of these pickups I don't know why, if they use some kind of nozzle, don't they direct the flow of exhaust through the nozzle at the turbine to speed it up?

The following is my theory:

Since the restriction is after the exhaust side of the turbo, the turbo vanes themselves sit in a pocket of lower flow, high pressure exhaust. That won’t spin the turbo much. With a traditional engine brake, the full amount of exhaust flows through at high speeds, but is time shifted from the exhaust stroke to just before TDC to provide the maximum resistance under compression.