This section covers cylinder heads and the head stud and bolt kits that hold them down, for BMW, Audi, VW, Mercedes and Porsche engines.
If you are adding boost to a European four or six, head studs are usually the cheapest insurance you will ever buy. Factory head bolts on most modern engines are torque-to-yield: they stretch permanently on install, cannot be reused, and lose clamping load as cylinder pressure rises — which is how a healthy engine ends up lifting a head gasket at the worst moment. A stud kit clamps harder and more evenly, and unlike a bolt it can be reused if the engine comes apart again.
Order studs and a fresh head gasket together; the head has to come off either way, and reusing a compressed multi-layer steel gasket is a false economy. Studs also need the block's threads clean and the correct lubricant on the nut face, because the torque figure assumes it.
See ARP head stud kits and engine fasteners, head gaskets and engine seals, and the wider engine top end range for camshafts and valvetrain.