Just recently rebuilt my 69 440 HP motor. When I put it back in the car, I find that I have developed a persistant exhaust leak at the flange. I am running Stock HP exhaust manifolds with a stock (H-pipe)system. Who makes a thicker and more surable exhaust flange gasket to stop the ticking?

Not sure on the "better" quality exhaust-doughnuts, but you might also consider more sturdy exhaust-hangers/supports.

Is your mounting-hardware (exhaust bolts/studs) in good condition? Sometimes new bolts/studs/nuts and even SS flat Washers provide better cinching-action.

Application of a little high-temp Ultra-Copper Silicone, applied to the exhaust-gasket helps too.

Finally, could there be a crack in the exhaust-pipe or manifold?

Thanks D C. I will try the Ultra Copper. All of the studs looked good and there were no cracks in the manifold. I have tried to find a thicker flange gasket, but have not had any luck. Any ideas on where to get a thicker one since I have to take the system apart anyhow?

Try some Percy's gaskets. Cost a little more but will seal anything. Good luck.

Must be somethin` badly warped/wrong in there. That combo isn`t even supposed to have a gasket.

Everytime I have had problems with the flat flange exhaust pipes not sealing it has been warped flanges causing the problem. When the manifold is off the engine it would have been easy to flaten them with a belt or table sander.
I have never had much luck with silicone by on exhaust fittings but the high temp has a repetition for sealing.
The D-rings are a major improvement of flat seals but are only on later madels. I think the class a motorhome 440 used them. The truck engine.
There are some heavy metal flange reinforcers. That are supposed to squish warped flanges into shape. Oreilly did carry them but they require space around the current flange that you may not have.