I have an in-line exhaust brake located after the cat converter. When engaged, the butterfly valve closes as it should and provides exhaust back-pressure to slow me down...all's well so far. Problem is that I can't build up enough back pressure due to leaks 1) between the front pipe and the cat 2) between the front pipe and the cast iron elbow, and 3) between the turbo outlet and the cast iron elbow.
Are there supposed to be any gaskets on either side of the elbow? I've tightened the clamps, but not much difference as the clamps don't make a seal around the entire circumference.
I'm thinking of getting the leak at (1) closed off by welding, but how to seal the other leaks?

 

When I installed my Jake, there were no gaskets between the elbow and turbo, or the elbow and down pipe.

The jacob replaces the elbow, and comes with a gasket that goes between the jake and turbo.

Maybe you could get one of those gaskets? Don't know if it would fit between the stock elbow and turbo, though...