I've been looking at making my own inlet recently. I've found some people who'll do an inlet flange for me to weld to. One person does a 6mm flange, the other 8mm.

Obviously the thicker the better to reduce distortion on welding but .... the 8mm is more expensive and heavier.

How thick is your inlet / how thick do you think it should be? It will have 1.5mm steel welded to it.

Finally - anyone want to convert crossflow weber carbs to fuel injection with a new manifold?

(guess what my current plan is before i do the same for silvertop and then make a complete silvertop inlet manifold reusing all the zetec parts).

If you can bolt it to the head whilst welding it up then I'd be inclined to go for 6mm in steel myself

mine is 6mm, as said make sure it is bolted to something solid, and take time welding it, mine got a tiny bit distorted, but not enough to ruin the seal.

but that was without bolting it donw (dont you love hindsight!)

mine was 6mm steel as above it distorted a bit by bowing from the middle about 3mm, but just put in the vice and gave it a tug with aid of an adjustable spanner for added leverage and came back flat. i done bit of a guide with lots of pictures if it helps.

zetec inlet manifold guide

Bolting to the cylinder head isn't an option - i want to make a jig so i have the option of making a few if other builders are interested. It may get bolted to another inlet manifold as part of the jig - but that increases my initial setup cost (and i'm out of work).

Last one I made I made a new inlet gasket from 2mm cork to compensate for any warping etc.
Cheers,
Bob

Tack it to heavy bit of steel weld it up and then break tacks, clean tack of job done.

And if its really bad, you can always get someone to take a skim off it.