the only reason a blowoff valve exists on any gasoline engine is because at shifts when the throttle valve closes, there is a pressure spike that has to be relieved. With a diesel (not just a powerstroke), the engine's demand for air may reduce at load relief or rpm reduction, but not sharply enough to require any pressure relief in addition to air flowing back out around the turbo and out the intake. now if you're having surge problems, follow 03f3507.3's advice.
save the blowoff valves for turbo'd fart can civics.
2002 Arizona Beige F250 Ext Cab Short Bed. 7.3L 6spd 4x4 140k
2" leveling kit, 285/75 Mastercraft AT2's,Napa BFF, DiPricol Pryo/Boost, DP F5 NS/stock/hi/40/80/120/140agg-lope, Toolbox, Audio goodies, IH shiftknob
muffler delete, CCV reroute, AIH/Foil delete,