9psi pulley netted us 425whp on the stillen kit on a 2010 6speed 370. With meth it would have made an extra 25whp without much fus. Generally you will pick up 10whp for each degree of ignition timing you can throw into the mix. Ofcourse there is a point of no return so make sure you find an experienced tuner to get the most out of the set-up. Most importantly with a meth set-up make sure your failsafes have failsafes. AEM makes a very nice Meth injection set-up. They also recently released their failsafe wideband AFR gauge.
Thanks,
Alex Goodwin
AlexG@motionlabtuning.com