Opinions wanted on cat back build up...

[Andris Laivins]

> Just out of curiosity, what's the typical depth of
> penetration for a weld bead?  If the reduction in
> cross-sectional area is similar for the crushed
> portion and the weld bead, then it would seem that the
> crushed pipe would outperform the weld since it is a
> smoother transition (no localized BL
> separation/reattachment which would be the case for
> the sharp discontinuity that the weld makes).

The depth of penetration is negligible if done right.  A nicely TIG welded tube
joint on a 16ga tube will have a tiny bit of penetration, like 1/16" or less
(probably less). A poorly MIG welded joint might have 1/8" , but the overall
cross sectional area is only slightly effected (and only for a short distance,
maybe 1/4").  A crush bend on the other hand will probably reduce flow area by
at least 10% ( a guess) and will do it over a much longer distance (the entire
length of the bend, several inches).  Its pretty easy to see then which method
is superior.  Looking under a car at a muffler-shop job and comparing it to a
welded mandrel-bends pipe, it is quite clear visually which will work better.

andris