Head stud kits

A head stud kit replaces the factory head bolts with studs, nuts and washers that clamp the cylinder head to the block. It is one of the first changes on an engine built for boost, because the head gasket can only seal as well as the fasteners clamp it. The category also includes head bolt kits for engines where studs are not practical.

With studs, each stud is screwed into the block by hand and the nut is tightened on top. That way, the threads in the block are not twisted during tightening, and the clamping load is more consistent. The kits are listed by engine in the title, and the listings give:

• the material: most often 8740 chrome moly or ARP2000, with Custom Age 625+ and Inconel for particular applications;
• whether the nuts are 12-point or hex.

Some kits use undercut studs, which have a slimmer shank between the threads.

Check whether the cylinder head can be lifted over studs with the engine in the car; on some engines it cannot, which is where a bolt kit makes sense.

Fit studs with a new head gasket. Chase and clean the block threads so the studs seat properly, and use the lubricant specified for the kit, because the torque figure depends on it. Tighten in the stated sequence and steps, and follow the maker’s advice on re-checking after the first heat cycles.