I have created a very basic model of exhaust manifold in solidworks. Following steps were followed while creation :

1) Created a basic outline of the base and the exhaust pipe ( using circles)

2) Joined the circles to the base by using boundary boss ( options selected were normal to the plane while joining circles to the base and while joining circles to each other ; options selected were tangent to the plane)

3) Used shell command to make the figure hollow

4) Material I have used for creation is chrome stainless steel