[MikeK]

A bit off the original rant, but a few comments on aluminum foundry castings, something I made for almost 30 years-

Most of what you see sand cast is either alloy 356 or 319, both Al/Si alloys. Aluminum has an extreme affinity for hydrogen gas. It goes into solution during the melt, then loses it during solidification. Efforts of varying degrees degas or remove some of the hydrogen before pouring. How much and to what limits is determined by customer spec, part function, and what the customer will accept. Removing all the hydrogen is not necessarily a good thing, it creates it's own problems with excessive shrink at final solidification points and hot tears. Add to that the added amortization cost of vacuum induction melting to produce near zero hydrogen castings, and customers say eek: I can get it done for half that.

Let me give you a bit of porosity analogy you can visualize-
Fill an ice cube tray with clear tap water. Air is dissolved in it, just like hydrogen in molten aluminum. Freeze it. You may get ice with visible tiny bubble streaks. This would be like an Al casting with visible pinhole porosity. If you say to the foundry 'how cheap can you...', this is what you get.

You may get ice that appears white because the air came out of solution, but not large enough to be visible. THIS is the benchmark for most aluminum foundry castings. They machine or polish fairly clean with possibly a few visible pinholes. For pressure apps, they need to be vacuum impregnated with a commercial sealant purpose-selected for the app. This will add $$.

You may get clear ice if you use degassed water and carefully control directional solidification (freezing). If you spec aluminum castings like this (ask for "degassed, no micro porosity, and pressure tight to xxx psi"), the price just went up 3X. Aluminum cylinder heads for modern cars are like that, and vacuum/pressure sealed on top of it. If they weren't, combustion gasses might seap into those 100,000 mile sealed cooling systems translating to $$$ warranty claims, and even worse, bad reliability reviews that kill sales. I can assure you that this degree of casting control is not the case with any aftermarket head or other part you buy for antique engines. If it were, the vendor would be bragging about it, but all the effort would never overcome the fine price/ yes-no line.