shhh! mention of a supercharger round here brings a hail storm of epic proportions.
most of what you get from doing this will be a randy bunch that has a lot to say about them but has never had any experience with them ,they just like to reprint what they read from someone elses post that never had any personal experience with them either.
or they try to turn you on to youtube videos of people tryin them but really have no knowledge of how to set them up.
just letting you know.
i have a question.
how did you find a RS4 3 with a .12 or did you buy it used?
in my opinion a .18 would give you the power you want but you already ordered a .15.
a good way to get the power you seek is engine modding and here is a link to a modding service and i beleive is one of the best.
www.rbmods.net
engine mods run about 125$
and will definitly be worth its weight in gold.
any other options i would recomend is CVD's all the way around and the 2 speed as you mentioned.
here is a link for gpm alloy upgrades.
http://www.asiatees.com/model.php?HP...&model=RS4%203
sorry about seeming harsh but you will see what i mean about the supercharger.
IMHO they do work but for the money you'll spend on it, you don't get much in return.
an engine mod would be better.