ARP Exhaust Manifold Studs

ARP’s exhaust manifold listings are header bolt kits and header stud kits, and most are made for a particular engine family. The bolt kits are the larger group. Heads are 12-point or hex, and threads mostly 3/8 in with some M8 and 5/16 in. The length is given as the under-head length (UHL) or the overall length, such as 0.750 in or 1.670 in. Drilled-head versions take locking wire, which stops a bolt backing out as the manifold heats and cools.

Stud kits make a manifold or header easier to locate when it is refitted. They also keep the wear on the nuts rather than on the threads in the head, which matters on an aluminium head that is taken apart often. Collector bolt kits for joining a header to the rest of the system are listed too, along with a few timing cover stud kits.

Many kits are stainless steel. Check the flange thickness of your manifold or header before choosing a length, and allow for any spacer or thick gasket in the joint. Too short a bolt will strip, and too long a bolt may bottom out.