Is “only to found out” grammatically correct?

To most Americans "only to find out" or "only to have found out" would be normal phrasing for most sentences. Of course only getting a piece of the sentence still leaves much room for error.

No, it's not correct. It should be "only to find out"

I don't see any situation where that would be acceptable. Might be one but I cannot think of it.

"only to have found out"

No. Context is important, one needs to read the COMPLETE sentence to see how the phrase is being used. Without benefit of that, I am guessing that this should read 'only to be/have found out'. Or, 'only to FIND out'.

"Only to find" would be better

no it should be only to find out. it sounds much better than found. the found word makes the sentence sound awkard

how would I know, im only 10 dumbass

As you didn't think it important enough to give us the whole sentence, we can only guess at what you really want to say.
We can correctly say: to find out; to be found out; to have found out; to have been found out.
But we can't say 'to found out'. If you have a piece of text containing it, please POST IT so that we can comment.

No. It's likely you mean "only to find out" (whatever).

"To find" is an infinitive. The infinitive is invariable. It is not conjugated. "Only to find out."

Only to be found out, if you are a criminal what? what did I say ?