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Porosity on the inside of the block

Practical Engine Building

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Upon inspecting the block for preparing it I have noticed a decent size porosity spot on the inner wall. Its not in a location that looks to be very critical. Is there anything that can be done to this spot or is something not to worry about? Is the block useable for a higher horsepower application? Its an aluminum I4 block

I have attached a photo of the spot

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I've never been able to detect porosity via simple visual inspection. Only by having an oil or pressure leak. If you suspect a porosity problem, I would seal the block and apply a vacuum (composite vacuum bagging equipment is useful for this). If there is a vacuum leak, and you can determine where it is, you can apply epoxy on the outside and the vacuum will suck it in and seal the porosity issue. I have successfully done this twice on oil-tank castings used in small formula race cars. BTW - I first sucked in solvents to remove the oil already in the castings.

That looks like a poor casting process, and finish, rather than "porosity" as such, which is where there is a path through the material (or weld) from one side to the other.

Before you start panicing, I'd suggest cleaning up the area with some W&D or polishing pads to remove the casting slag and see what you're actually dealing with. I would expect it to be only on the surface and not an issue for using the block.

Oh, what does the outside look like?

After cleaning up the area this is what I am looking at. It has a small recess in that area. It doesnt go through and the other side of the block looks just fine.

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