For short-arc welding, which I've done a lot of (typically using solid
.035 dia or .045 dia wire), I used about 40 cfh (cubic ft/hr). But you
could experiment with less, until you have problems with porosity. I
suggest you experiment on scrap material, rather than your race
vehicle. Too much gas flow could be bad, because it tends to suck
in air from the sides, due to the venturi effect. Please remember, also,
that air movement such as wind will affect your shielding-gas coverage.
And contamination, such as grease or paint, will absolutely destroy your
weld. When it comes to welding, "cleanliness is next to godliness."
tallguy