Lots of paralell http requests in node.js

I've created a node.js script, that scans network for available http pages, so there is a lot of connections i want to run in paralell, but it seems that some of the requests wait for previous to complete.

Here is the code fragment:

    var reply = { };
    reply.started = new Date().getTime();
    var req = http.request(options, function(res) {
        reply.status = res.statusCode;
        reply.rawHeaders = res.headers;
        reply.headers = JSON.stringify(res.headers);
        reply.body = '';
        res.setEncoding('utf8');
        res.on('data', function (chunk) {
            reply.body += chunk;
        });
        res.on('end', function () {
            reply.finished = new Date().getTime();
            reply.time = reply.finished - reply.started;
            callback(reply);
        });
    });
    req.on('error', function(e) {
        if(e.message == 'socket hang up') {
            return;
        }
        errCallback(e.message);
    });
    req.end();

This code performs only 10-20 requests per second, but i need 500-1k requests performance. Every queued request is made to a different HTTP server.

I've tried to do something like that, but it didn't help:

    http.globalAgent.maxSockets = 500;