Metal expands when heated.. we all know this... so
give it the room to expand and dont let it warp the
flanges... if you give each tube a slip area it will
slip instead of warping.. by that I mean drill one
of the mounting holes larger(per tube).. if you have
3 holes per tube drill out 2 of the holes to slide..
you keep 1 hole to locate the tubes..I like
a gragfoil (graphite on stainless material) to let
it slide easy... cut each flange from each other
(ends are cut from the center tubes)... all it takes
for a leak is just a small amount of compression loss
at the flange to get it started and it progressively
gets worse with each heat cycle... cheapo (thin) flanges
make it much easier to warp... thats why I use 3/8"
flanges on all the headers I build
