12-18 psi on a stock mustang?
I hope you've got a lot of money hangin around...
Even though the 4.6 intakes are "fixed" in the 99-up Mustangs, they're still plastic...
and I guarantee they will not handle 12 to 18lbs of boost for long.
The stock bottom end\internal (pistons,rings) won't be able to handle it either. They just weren't made for that kind of punishment.
If you're going the supercharged route, be sure to get your exhaust done first (X\H-pipe, catback, possibly headers) to get the most gain from your forced induction.
I would suggest some exhaust work, gears, a good shifter, and a blower with no more than 8psi for a near stock daily driver.
The MAF may also need to be re-programmed\replaced, as well as your fuel injectors and fuel pump. This all depends upon the year of the car, the blower kit you're using, and how much you want to spend.
Any more than 8 psi, and you may be pushing it for a daily driver, and 12 psi or more should have a built bottom end in my opinion....
If you're looking for a street blower, I would highly recommend the roots type that replaces the intake. Its fairly reliable, easy to maintain, and gives GOBS of torque at 6psi.
Just my 2 cents...
------------------
Adam "Hammer" Packett:
Moderator, Gulf War Veteran
GO GET 'EM BOYS! 