Exhaust manifold

Abstract

An exhaust manifold includes a head flange member, a plurality of branch pipe parts and a collector pipe part. The head flange member has a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine. Each of the branch pipe parts has an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface. The collector pipe part is connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts. An area of the cylinder head mounting surface is smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.

What is claimed is: 
     
         1 . An exhaust manifold comprising:
 a head flange member having a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine;   a plurality of branch pipe parts with each of the branch pipe parts having an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface; and   a collector pipe part connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts,   an area of the cylinder head mounting surface being smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.   
     
     
         2 . The exhaust manifold according to  claim 1 , wherein
 a surface of the flange main body portion and the cylinder head mounting surface are connected with a step-shaped level difference in-between.   
     
     
         3 . The exhaust manifold according to  claim 1 , wherein
 the head flange member defines a through hole in a position that avoids the branch pipe parts.   
     
     
         4 . The exhaust manifold according to  claim 1 , wherein
 the cylinder head mounting surface is disposed outwardly of a surface of the flange main body portion when viewed along a direction parallel to the cylinder head mounting surface.