an outer cylinder depending from the insulation cap and at least partially surrounding {HEAD ~ the inner cylinder} to define {TAIL ~ an annular exhaust gap} for exhaust gas from the exhaust plenum 
to define
an outer cylinder depending from the insulation cap and at least partially surrounding { HEAD ~ the inner cylinder } to define { TAIL ~ an annular exhaust gap } for exhaust gas from the exhaust plenum
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH