increasing boost increases the amount of air .. more air = more diesel that can combust during the compression stroke .. diesels typically only run somewhere between 70-85% percent efficient .. the less diesel that is coming outta your engine and burning up in the exhaust pipe the cooler the EGT's will be .. typical example is with a diesel gas system .. diesel gas uses a small amount of LPG as a catalyst to burn more of the diesel on the compression stroke resulting in somewhere between 25-45% increase in power, but also lowers egts as it is around the 97-99% efficient. Its one of the reasons why when you blow an intercooler/turbo hose you feel a significant loss of power, you also see massive clouds of black smoke (unburnt fuel) and your egts climb through the roof ..
DPF (diesel Particulate Filters) and EGR Systems are some of the ways that manufacturers overcome the emission systems side of the equation ..
Wade

