Patent ID: 7171934

Claim:
An intake manifold comprising: a branch pipe for connecting a cylinder head of an engine and a surge tank, wherein the branch pipe includes a first portion a passage sectional area of which is gradually increased from the cylinder head toward the surge tank, a second portion extending from the first portion and having a constant passage sectional area which is larger than that of the first portion, a third portion extending from the second portion and a passage sectional area of which is gradually increased, and a fourth portion extending from the third portion and having a constant passage sectional area which is larger than that of the third portion, an end portion of the fourth portion being connected to the surge tank, wherein the following relations are established: ( A+B )/ X =0.22 to 0.30, C/X =0.38 to 0.43, D/X =0.18 to 0.22, E/X =0.07 to 0.15, D 1/ C =0.24 to 0.30, and D 2/ E =1.05 to 1.85; where X represents a total length from an opening of the branch pipe ( 11 ) on the side of the cylinder head ( 1 ) to the surge tank ( 5 ), A+B represents a length of the first portion, C represents a length of the second portion, D represents a length of the third portion, E represents a length of the fourth portion, D 1 represents an inner diameter of a perfect circle that has a same cross sectional area as the passage sectional area of the second portion, and D 2 represents an inner diameter of a perfect circle that has a same cross sectional area as the passage sectional area of the fourth portion.