The hose has three functions, one is to allow the hard pipes at both ends of the hose to have slight relative displacement, which is a better way to deal with the vibration, also a method to compensate the thermal deformation; the second method is to retrieve the manufacturing errors make two hard pipes that need to be butted. It doesn't have to be very accurate. It is meaningless to improve manufacturing accuracy increase manufacturing cost. Both effects should be considered when using hoses on the intake manifold. The third one is universal. As long as it can be obtained the length is enough, the bending shape does need to be considered.

 For carburetor throttle body gasoline injection engine, intake manifold refers to the intake pipe carburetor throttle body to air inlet of cylinder head. Its function is to distribute the air fuel mixture in the carburetor throttle body to the air inlet of each cylinder.

 For air channel fuel injection engines diesel engines, the intake manifold distributes clean air only to the intake ports of each cylinder. The intake manifold must distribute air, fuel mixture clean air to each cylinder as evenly as possible. Therefore, the length of the gas flow path in the intake manifold should be as equal as possible. In order to reduce the air flow resistance improve the intake capacity, the inner wall of the intake manifold should be smooth.