In colloquial language, both are correct, and you can omit do.

But from a grammatical perspective, I guess the former is the correct one, because technically we don't have a way of knowing whether engineers is the object or the subject, and the latter could be translated as:

He really does know more about cars than even about the engineers.

which is a problem!

In colloquial language, both are correct, and you can omit do.

But from a grammatical standpoint, I guess the former is the correct one, because technically we don't have a way of knowing whether engineers is the object or the subject, and the latter could be translated as:

He really does know more about cars than even about the engineers.

which is a problem!