I've heard that this gives descent gains but no idea what it is. Thanks

 

It's basically a 4.7kohm resistor installed in your IAT connector. This resistance makes the PCM think that the incoming air temp is always 57 degrees F and allows for the most aggressive timing curve.

SLP sells a version of it for about $20 that will make for a much cleaner installation than a resistor stuck in there. I use one and it's given me anywhere from 0-1 degree of advance. Nothing special really. I'd recommend Autotapping it if you do choose to install one, just to see the impacts.