For 1996+ Vortec (l31) or Edelbrock E-TEC heads, manifold has a balanced 180+ firing order, contains exhaust gas heat riser, offers excellent performance potential, front oil filler tube boss included, carburetor center-to-center dimensions = 5-1/2 in, also available polished PN[5419] but not fit HEI, use Rochester 2GC (small 1-7/16 in bore)