Exhaust brake

[Chamberpains]

I let my cm870 fly up to 32 psi on extreme hard down hill braking with no problems ever. Steep goat hills with 10% or greater grades with sharp curves demand this kind of engine brake use as to not smoke the actual brakes. The cm870 is a tough engine if it's well taken care of. As rawze stated the ECM will adjust the back pressure according to demand and settings. It would settle in at ~28ish on most declines.

With gross 80,000 #s it would hold me in 9th gear @ 50-55 mph, and 45mph in 8th on most mountain grades with very light braking. I would maintain the boost @ 25-28 psi using the foot brake as assistance the entire way down the mountain. Don't be afraid to let it do the work. It'll save you a pile on changing brakes in no time. But you have to let it get up in the rpm range. If the decline demands it keep the rpms above 1550. I wouldn't let mine go above 1850-1900 rpm all though on a couple ultra rare occasions I accidently grab the wrong gear early and let it fly up to 2100 rpm and had no ill effect. though I quickly stomped the brakes to get it down in rpm's. Anything below 1500 and they were just noise makers.