66-67 Dodge Charger Source Guide

Exhaust Manifold Q & A


Jeff Brookings: I have a set of HP 440 exhaust manifolds and since this is the first time I haven't used headers, I need to know about the exhaust sleeves and manifold nuts. What is the setup for these? Are there different sizes?


Aarin: The manifolds are installed using studs and nuts. The studs are 3/8 coarse into the head and 3/8 fine for the nut. It is important to use the right length stud or else you can't slip the manifold between the stud and the inner fender. You will use 9 regular nuts, 1 short sleeve nut on the left and 2 long sleeve nuts on the right.

They repro the sleeve nuts and they are available from many sources (watch out because some "repo" kits have the too-long studs.) Make sure you use HP gaskets for the headpipe which are 2 1/2" - some parts stores will give you 2 1/4" . If you are very careful to center these (the HP ones) you will not get leaks.

One last item - the headpipe flange changed over the years (they rotated only, they are still the same plane) so make sure you have the right set for whatever headpipes you buy ( I think the Year One catalog has a quick illustration to show the varieties) Don't forget thread sealer as the studs go right into the waterjackets and leaks here are a big problem.

Exhaust gasket leaks are primarily caused by the gasket being misaligned and actually hanging into the path of exhaust gas flow. The portion of the gasket will start to burn and 'wick' the burn through its surface and out to the atmosphere. This is true at the ports or pipes. If you can have the gasket centered, where it is slightly recessed as far as gas flow is concerned, and get a good even clamp, you will get good life from the gaskets.