If they are stainless bolts going through aluminum manifolds use some type of antiseize or the bolts may seize on the aluminum. There is no engine builder I know that ever recomended lock washers on an exhaust manifold. I have always been told to use a plain washer. Exhaust manifold washers are usually a little thicker than a standard washer I believe to deal with the additional heat. Rick G.

I think what Rick meant is if you are using stainless bolts going into aluminum "heads" use an appropriate antisieze. Then again, I think stainless fasteners are only for "pretty" engines and not "working" ones. And yea, thick washers or flanged bolts, not lock washers, they break and fall out and then the bolts are loose