Anyone know what max temps they have seen their intake manifolds achieve?

I'm assuming this is for your custom manifold, correct me if I'm wrong. What is it you're trying to figure out?

Unless anyone comes up with any other measured data the best we can do is have a guesstimate.

It'll depend on whether it's dry, wet and what's under it in terms of the exhaust manifold. Extractors are likely to radiate a little more heat since they can't conduct much back to the head. If it's a wet manifold, normally it'll never exceed ~100°C, dry it might get hotter from radiated heat off the exhaust. I don't have any solid numbers (nothing to measure it with) but I found I needed a heat shield under my ITBs, even with it they still get hot to touch, say 60°C ish. I have extractors, unwrapped.

Your manifold sections look to be substantial in the photos so it'll probably conduct a good amount of heat back to the head which is maintained at around 90-100°C, the gasket will have some minor insulating properties. You could probably assume the manifold wont get past 150°C at a guess. If that's not stretching anything then no worries, if it is you might want to get a thermal gun and take some measurements. Or, water boils at 100, that'll give you a crude measure by dripping it on.

Hope this helps, this data always seems hard to come across.

I ask because I was going to braze the two halves together with 450 degree melting point aluminum solder vs TIG welding.

That should be fine in my humble opinion, keep in mind that many modern cars use thermoplastic intake manifolds.

I would guess less than 212F (100C) and that is only from heat soak (hot engine turned off) -- most A12 manifolds are bolted to the exhaust manifold. While running it will be much cooler

Thanks for the help guys.

I am going to keep with the hardware to clamp, and braze the pieces at the seams. I want to take extra measures to keep from getting any air leaks.

Now back to plenum design.

that alloy solder today is great gen 2 flux free
used it to repair my manifold on a 13b rotary
which gets even hotter than conventional engines.
You can also run a plastic spacer plate like
some race engines do to avoid inlet mani heating
up from the head temps and also sand blast your
billet work on the inside for better atomisation