LQ4's get the 3.1, lower compression than LQ9.

 

I have used a 2.75" Pulley with my Radix and have opted for a 2.9" instead on my 5.3L I put it on a Dyno with the 2.75" Pulley to see if I could work with it but I was way down on H.P. instead I took it off.
If someone can tell me how to post the charts on this board I will show them, or go to www.chevyavalanchefanclub.com and look for one of my posts amtg4u

Hope it helps a little