Design and weld quality are more important than the flavour of ally used... little shape/flat sides + outside corner joints = the flat sides flex/ballon under boost which concentrates stress on the welds. If the welds are partial pen/have LOF (lack of fusion) defects/crater defects etc then they will crack (sooner rather than later) like these did
http://www.migweb.co.uk/forums/welding-fabrication-painting/428492-what-causes-alloy-welds-crack-pics-inside.html
http://weldingweb.com/showthread.php?t=60301
Some of the alloy choice comes down to the way you go about making it for example if sectioning tube* to get something with shape then you have a choice of a 6xxx series or a 6xxx series alloy. Either would be fine . If shaping it out out of flat sheet then a lot more flavours to choose from, 1050 or (preferably) 3103 would be the better choices. I'd avoid the 5xxx series which leaves a 6xxx series for the plate to make the mounting flange from, typically 6082 as that's a common flavour in plate thicknesses (and also one of the common suspects offered as tube the other being 6063)
* availability (in the UK at least) might be a stumbling point but D section extrusion exists in sizes that lend itself to plenums
can use pipe cut in half like this.
Hi,
I cant claim these to be my manifold just using it as an example.
do you mean the swage on inlet runners?
if so I have seen those done in a press with a mandrel I will try and get a picture of it for you.