Chapter 9:Dry Exhaust Systems
Figure 9-20. Fiberglass insulation cover
(Courtesy Applegate Industrial Materials,
Inc.)
nearby or overhead panels, particularly the
inside of an exhaust trunk. The very best in-
sulation method includes a layer of sound-
deadening insulation (there is plenty of noise
in the exhaust piping) outside a layer of heat
insulation. Both may be fiberglass. A^3 / 4 -inch
(19 mm) layer of fiberglass heat insulation
backed by an inch of fiberglass sound insula-
tion that is faced on the side toward the
exhaust pipe with a 2-lb./sq. ft. (9.8 kg/m^2 )
mass-damping lead sheet makes a good com-
bination. All, however, must be fiberglass (or
one of the still more fire-resistant materials)
and rated by the U.S. Coast Guard as accept-
able fire-resistant insulation for marine use.
If space is a problem, a sheet of^1 / 2 -inch
(12.7 mm) Marinite board will serve to insu-
late the inside of the exhaust trunk, though
somewhat thicker is preferable. This will not
have the sound-deadening advantages of
thicker, softer fiberglass insulation used with
or without the mass-damping lead sheet.
Another option is to use^3 / 8 -inch (9.5 mm)
Marinite or Transite board against the inside
surface of the exhaust trunk faced—on its
exhaust-pipe side—with corrugated sheet
aluminum or steel. (Aluminum is superior,
as it’s lighter and won’t rust.) The key is
that the corrugations must run vertically,
opening at the top and bottom of the trunk.
Natural convection drives cooler air up
through these corrugation channels, form-
ing a good insulating air cushion. Also, the
metal reflects some heat back. The draw-
back to this method is poor sound deaden-
ing (Figure 9-22).Figure 9-21. Wrapping an exhaust pipe (Courtesy Culimeta Textiglas Technologie GmbH &
Co.)
boats) require insulation rated at continuous
temperatures of 2,000°F (1,100°C). Also, the
exhaust manifold on dry exhaust systems is sel-
dom insulated. It’s difficult to do so properly—
that is, to make it stay in place and also retain
good access to the engine for maintenance and
repair. If used, however, insulation for exhaust
manifolds should be rated for 2,000°F
(1,100°C) continuous. (See Appendix D for
insulation sources and products.)
Keep in mind that you need to insulate
not only the exhaust piping itself but any