I was wondering if some of you guys could offer some advice on my set up.

I made a custom aluminum plenum for my race car. Everything was TIG welded and I just used the filler rod that the guy at the LWS gave me (don't remember).

Anyways, The plenum is very wide so it would bulge out under boost pressure and then suck back in from vacuum when the throttle plate was closed. This caused an "oil can" effect which eventually cracked my weld right down the middle of the bead.

I have since reinforced the top of the intake manifold to keep it from flexing under boost and vacuum. However, I am wondering if the weld was just not as strong as it could be. Mainly because I watched the video online of the guy who OXY welded two aluminum sheets together using flux (obviously). He then proceeded to beat the piss out of it, shape it, smash it, stretch it and then shrink it. He abused this thing for a while and the weld never gave. So I am thinking my weld was inadequate since it cracked from just a little oil canning of the plenum.

What do you guys think? Unfortunately I don't know the grade of aluminum that was used as the brake metal or the filler rod I used (I think 4043 rod). Maybe a particular filler rod would be better? I don't think it is a matter of penetration due to the fact that it split right in the middle of the weld right?

I just don't know. Maybe the answer is simply reinforcing the top like I did to keep it from flexing. It has held up fine ever since then, but it is still something I think about.

Here is the weld.

Here is a picture of the plenum before I reinforced it. Lots of surface area allowing the top to flex a bunch.