Setting your Site Collection Search Settings by Powershell, what a tongue twister, try saying that six times fast. Setting your search settings via PowerShell is not something that is immediately obvious and requires a bit of digging.
First – how do we see what settings we’ve currently got? First lets get our web and throw it into a variable to make it a bit easier to handle.
$web = get-spweb http://address
By digging down through the properties of the $web object we can see two areas that might house this : allProperties and Properties. I do not know why there are two property areas, seems a little confusing.