[Richard Hudgins]

Folks,

The normal method for sealing slip fit headers is to install them with liberal amounts of a heavy grease such as wheel bearing grease. (Note: this only works if the slip fits are reasonable. IE: .050 on the diameter cold.)

This is the method used in the aircraft industry and has been around since air cooled turbo charged engines came into common usage.

They do expand a bit and the headers do as well.

Has always worked for me from lowly Formula Fords to Inconel F1 headers.