Torque refers to how tight a bolt should be tightened. If you overtighten a bolt, internal stress cracks will occur, leading to early bolt breakage. Engine designers specify torque settings just before bolt breakage, since undertightening a bolt is an underutilization of the strength of the bolt. There is a direct correlation between bolt size and torque setting.
You must use the bolt specified for the particular engine. ARP offers data for each engine make and model, and the corresponding head to cylinder bolt. For example, the Chevrolet 348 big block engine, with cast iron heads, uses bolt part number 135-3602.
According to the Summit Racing Organization, the torque setting for a Chevrolet small block V-8 is 65 foot-pounds. Since ARP recommends using OEM specifications, this is the torque setting you would put on an ARP cylinder head bolt.
The Chrysler 426 Hemi engine has two torque specifications for the heads. For cast iron heads, the listed torque is 70 to 75 foot-pounds. For aluminum heads, the listed torque is 65 to 70 foot-pounds.
The head bolt specification for Ford 260, 289 and 302 engines is 65 to 72 foot-pounds. Because this is a wide variation, if you are using aftermarket aluminum heads, cross check this specification with the head manufacturer to ensure you are in compliance with the OEM recommendation.