Balancing pistons

I bought a set of off the shelf Manley forged alloy pistons for my Ford 4.6L V8 build and after weighing them and matching the heaviest ones with the lightest wrist pins and so forth, four of the piston/wrist pin pairs are within 0.1g straight out of the box. The other four were 0.4g over, 1.4g over, 1.6g over, and 3.9g over. I ground the .4g off the wrist pin boss and I had to take a surprising about of material off to get it off. That makes me a bit uncomfortable taking 1.4g, 1.6g, and especially 3.9g off the others. Seems like I’d have to take off so much material that it might weaken the pistons. I include a picture here of the piston I ground .4g off of for reference.

so my question is, am I being paranoid about grinding so much more off the other pistons? What is the maximum weight that one can safely grind off the bosses of forged alloy pistons? Or should I be considering contacting the vendor I bought the pistons from about exchanging three pistons for ones that are closer in weight to the others.

3.9 g is more of a variation than I'd be happy with so absolutely I'd be trying to get them closer. Yes, you do need to remove quite a lot of material to make a difference to the weight of the pistons due to the aluminium material. You may not be able to safely get a full 4 grams out of the heaviest piston but you can remove much more material than you have without impacting strength. In particular you can remove material from the 4 places I've highlighted in the attached picture. Basically you want to make sure you don't reduce the thickness of the material to the wrist pin boss and you can see on these 4 corners there's a fair bit of excess material. This is one of the common places I'll grind material away.

Thank you Andre. I did not see an attachment, but I think this is what you mean, correct?

Just wanted to mention that Manley has really great customer service. I called them up and spoke to Johnny and he agreed to exchange the heaviest piston with one closer to my target weight free of charge. He did this even though I bought the pistons from a 3rd party vendor. I am very happy with Manley’s customer service right now.

Sorry I'm not sure what happened to my pic. I'll try again.

That's great that Manley were able to help you out. Always nice when a company goes above and beyond since it's sadly lacking in our industry!

That makes me feel good. After studying the piston some more I came to the same conclusion. Yes, sadly good customer service is something that is not as common as it once was. It was good to find out they have it.