America's favorite high-performance cast iron small block cylinder heads offer big power and bigger value. Chevrolet Vortec Cylinder Heads' fast burn combustion chamber and high-velocity ports combine to produce big horsepower. Vortec Heads can be mildly ported for additional performance and milled up to .040'' for increased compression ratio. The Vortec Heads come with various intake and exhaust valve sizes to complement the high-velocity port design and your performance needs. Vortec Heads outflow Bow Tie Heads right out of the box and are a 20 to 40 horsepower bolt-on increase over earlier cast iron small block heads.