Ivylog wrote:
AH64ID, guess you did not read my post above as during the use of my true Jake (compression release) brake yesterday, I had 12 to 15 psi of boost depending on the rpms, not how long it was on. Guess that loud sound of a truck without mufflers while using a Jake is not lots of air coming out the stacks by way of the turbo.
It is very odd for a compression release brake to build boost. There isn't any additional flow out the exhaust with the brake on or off, therefore there should be no change to the turbo speed.
What model engine? Does it have a VGT that may be closing the vanes at the same time as the compression release brake?
Are you building boost decelerating at higher rpms with the brake off?
How much boost do you build in N at 2,000 rpms? This will be more boost than you can build without fuel at the same rpm.
How would the air go any other way but by the turbo?
EDIT: I see you said you have a ISL 400. That motor uses a VG Turbo which tells me that the turbo vanes are closed to provide an exhaust braking feature. That feature increases the boost which then increases the compression release retarding power. So it is a hybrid system of sorts.
An engine with only a compression release brake and a non-VGT turbo shouldn't build boost while braking.
Looks like it is called a C brake by Cummins and they claim an additional 40hp of retarding power by using the VGT in conjunction with the compression release brake.
