Hey Jimmy, don't know if you run this plugin for vB but it has reduced spammers from 10-20 a day to 1 a month on our forums:
http://www.vbulletin.org/forum/showthread.php?t=176481
not sure if it will work on 3.8.6, I'm running an older version, but do check it out.
if the subscriber's email or IP is flagged in this database:
http://www.stopforumspam.com/ they are unable to register at your site
so not only does it stop bots, but humans too who are known to spam
edit: also use
http://www.vbulletin.org/forum/showthread.php?t=132482
which is hell for bots, easy for humans, set some RC specific pics (wheels, body, suspension etc) and ask them to click the pic that matches the word