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thems purdy Mr. P.
I've never used 2" headers before, I've never had issues sealing up cheap 1 3/4" does the extra 1/4" make for a trickier seal? I never thought about it needing some expansion room.

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The 2" tubes does have its problem... again on the
center ports... with the larger tubes you have a bit
less room between the 2 center ports which gives it
less gasket/sealing area and thats where most headers
tend to leak.. a thicker flange usually helps that..
even on a production manifold we allowed for expansion
(if you look at the holes).. also what Fred posted
and the production manifolds not running gaskets..
yes thats true BUT a manifold is a TOTALLY different
design than a header flange.. the manifold has thickness
to keep it from warping unlike a 5/16 flange(which
most headers have).. I use 3/8 flanges to reduce the
warping along with the larger hole set up... also
most headers have the weld bead on the gasket surface
which is a plus and a negative ..its a small area
that bites into the gasket to seal BUT it also cuts
as it grows and contracts
EDIT
You have to figure in expansion on the exhaust... a
standard size car with full exhaust and normal temp
will have 3/4"+ growth at the tip of the tail pipe

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