Problem with maximum concurrency users

I have written some simple app on meteor, and then I wrote some test with “meteor-down” to test how
much concurrency users it can provide and test show there it can’t provide more then 400 concurrency users.
Does then any way to increase count of concurrency users which app can provide?

I have run same test for meteor test server and counts was up to 50 000, just because my pc don’t provide that test for more then 50000 concurrency users