Cummins engine brakes are called Jackebson engine brake, better know'n as the jackeb Brake. This is how they work simply stating, Energizing the brake converts a diesel engine into a energy absorbing air compressor, this is done by opening exhaust valves near the top of the compresion stroke, releaseing the compressed charge into the exhaust, the energy used to compress the charge without a firing cycle acts as a brake.. engine brakes are made for steep grades downward decent, to save on drum wheel brakes, and the possibility of over heating drum wheel brakes on a downward decant,whitch is also know'n as smoked the brakes, because of brake shoes overheating. Heat will glaze brake shoes to the point where you will have no brakes. I know Isuzu has exhaust brakes so call a dealer and ask them about it.
1977 31' landyacht Sovereign