High pressure pump and manufacturing process thereof

A high pressure pump comprising a housing and a cylinder in said housing wherein a shaft-like plunger makes a reciprocating motion in a bore formed in said cylinder to compress a fluid fuel;

• said high pressure pump, wherein
• one end of said plunger is connected to a compression chamber for compressing the fluid fuel, while the other end is connected to a reciprocating motion drive source through a member;
• wherein a transverse aperture is connected with the bore through a cylindrical groove provided between axially opposite ends of the bore of said cylinder;
• and the clearance between said bore and said plunger depends on the axial location along said bore, wherein Ga≦Gb<Gc or Ga<Gb≦Gc and, wherein:
• Ga denotes a clearance between the bore on the portion from said compression chamber to said cylindrical groove and said plunger;
• Gb a clearance closer to the cylindrical groove, out of the clearances between the bore from said cylindrical groove to the drive source side and said plunger;
• and
• Gc a clearance closer to the drive source side, out of the clearances between the bore from said cylindrical groove to the drive source side and said plunger.