Reduced exhaust braking after demandate

[DVT873]

These "potato in the tailpipe" engine brakes are pretty useless with manual transmissions. With Allison automatics they are pretty good. The brake drops the RPM a bit which makes the transmission downshift. The trans is actually doing the braking. I first saw these on the Nissan UD trucks back in the late 80's. All manual trans. That brake was standard equipment. They did very little. Maybe on a steep grade? There had to be a reason they were standard.
Jump to the late 90's and they became an option on International with the DT engines. Road testing a tandem with an Allison and a new garbage packer I tried it. I was surprised. At about 50 MPH it slowed quick enough to push me aginst the shoulder belt.