JB Weld and PC-7 are very good products.
JB Weld has recently come out with a 5 minutes version (red). But my experience with epoxies in general has shown me that longer setting epoxies are stronger. So stick with the good old 12 hour version (black).
PC-7 has added micro fibers. So is more of a paste.
There are other name brands like Permatex with simmilar products. And I'm sure they work as well.
Use a degreeser first !
The best are made in the Philippines, Cord Steel Epoxy & Pioneer Steel epoxy are what i use on my tuned carters they absolutely harden like rock (well almost), i use the quick drying epoxy as they are tougher when fully cured.
Ive tried JB weld (black) and it seems good, they promise that it can handle ~300C* so thats more then enought.
Ive also tried some kneedeble steel from holland and some steel epoxy from sweden, they all work good cause it dosent get very hot. The epoxy from sweden ive used for over a year now with no problems but ive switched to the dutch kneedeble cause its easier to handle and its just as good.
The JB weld I havent tried for very long but its hard as a rock!