do you even know what spot welding is? you are talking about arc welding but you are calling it spot welding. now go on the internet and look up the difference in strength between a mig weld and a tig weld. tig welding is more for looks, when something is small and needs to look pretty the tig weld it. turbo manifolds ara semi high pressure but not at all what you are making them out to be. mig welding is much stronger. you can calim to have seen whatever, if what you say really happened then you need to find a competent welder.