What are they and how do they increase performance?

 

stock ratio is 1.5 and is a 'non' roller. a roller rocker wether its roller tip or full roller will ride on , well rollers which decreases friction in your valve train, less friction = the less the engine has to put into it to operate. and 1.5 vs. 1.6 means that if the cam pushes up .500 with a 1.5 roller rocker itll be .750" while a 1.6 rocker will give you .800" lift

 

In a basic nutshell 1.6RR's replace the stock "stamped steel" 1.5 ratio rocker arms. In terms of performance they allow you to get more lift from your camshaft whether it be stock or something larger. I would expect 7-10hp or so.

Ex. lets say your cam has a .510" intake lift and .520" exhaust lift with stock 1.5's...
...With 1.6RR's your new lift will be .544"/.555" which will provide you with the benefit of a few more ponies

Here's how to calculate that: .510"/1.5 = .340" x 1.6 = .544" .520"/1.5 = .347" x 1.6 = .555"