Sitecore.ContentSearch.Solr.DefaultIndexConfiguration.config.maxSearch.xml

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <!-- Code omitted... -->
    <settings>

      <!--  CONTENT SEARCH SEARCH MAX RESULTS
            The max number of results that a query returns.
            If a limit is not specified in the query (ie Take(10)) the search will use this value to set the number of rows returned.
            It is important, for performance, that only the rows you need for a single request or page of results is returned.
      -->
      <setting name="ContentSearch.SearchMaxResults" value="500" />

    </settings>
  </sitecore>
</configuration>