The ornamental design for an exhaustmanifold, as shown and described.
FIG. 1 is a first side elevational view of my exhaust manifold showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a second side elevational view thereof;
FIG. 4 is a bottom elevational view thereof;
FIG. 5 is a top elevational view thereof;
FIG. 6 is a perspective view thereof; and,
FIG. 7 is a rear elevational view thereof.
The broken line showing of the inlet and outlet of the exhaust manifold is included for the purpose of illustrating environment and forms no part of the claimed design.