Aluminium manifold material

[scottmk1]

Hi folks, a future project will be to make an aluminium manifold to fit bike carbs to a Vauxhall redtop engine. What grade of aluminium would be best for this considering it will be a plate about 10mm thick to make the flange and 3mm wall thickness tubing to make the runners, and it will be tig welded together once all parts are made.

Cheers

Scott

 

[hotrodder]

With tube you generally get naff all in the way choice, a 6xxx series is about it with some sizes being available in both 6063-t6 and 6082-t6. Of the two there's not a lot in it, 6082 is more common/wider range of sizes, machines a bit more nicely, is a bit harder/stronger and thus less formable

More choice with plate, any of 'em will do although 6082 will again be the hardest (read, resistance to marring on the gasket surfaces etc) and nicest to machine. If machining the gasket flange instead of taking a drawing to the local profile cutters then flat strip is convienent/cheap and being an extrusion is like tube- virtually always a 6xxx series, mostly 6082.
6xxx series can be welded with various flavours of filler, 4043 or 5356 being the most common

 

[scottmk1]

Thanks hotrodder, The runners will need formed at the flange end as the ports are oval there, and making the flange will be a mixture of hand tools and a small manual mill/drill. Is it best to cold form 6xxx series tubing or does a bit of heat help?

 

[hotrodder]

Hot working or annealing* will make it easier but isn't necessary to ovalise the ends of a bit of tube

* can use a bar of soap, a permanent marker or if using oxy as a heat source soot as crude temp indicators- soap marks turn black at around the right temp while soot and ink burn off. Strictly speaking the heat treated alloys need to soak at temp for some time for a full anneal but simply heating softens 'em a bunch, cooling rate not important