In marine trim we don't use any EGR, and I am not very familiar with the
various systems over the years. However, the question posed was as to why
heat the manifold when you are intercooling (seems to be cross purposes)? One
possible answer is that at light loads one would want a warm intake manifold
to assist in fuel vaporization (throttle response and emissions). Since light
load operation is by definition throttled, there is no real volumetric
efficiency penalty. Also, since boost is down, the intake charge is cool. A
turbo engine at WOT however has high intake charge temperature (hence the
need for intercooling). The airflow at WOT is so high that there is no
appreciable temperature rise in the intake charge going through the heated
manifold. If the engine were designed for WOT ONLY, one might not heat the
manifold. Otherwise, manifold heat is generally beneficial.

Jon Lauter
Rotary Power Marine Corporation
www.rotarymarine.com

 
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