Few Questions...
 

Recently I just sold my Roush and purchased an '03 Cobra. As of right now it has the pulley upgrade, o/r x-pipe, Custom Tune, a ram clutch, and a belt tensioner. It made 460 to the rear wheels, and 480 torque. I was wondering what the stock motor could handle and what are the best modifications for the buck are? I'm new to the 4v. My goals are to be around 550-600, without changing internals, at least not yet.

I believe its 600rwhp.

The '03 cobras have an iron block and forged internals, so they already come bullet proofed from the factory. Sounds like you already have the basic bolt-ons. The main limiting factor to reaching 550-600 rwhp range is the Eaton blower. Me thinks you need to look into either getting a KB or Whipple for the power your wanting. If you have the cash and want to make some serious power, maybe a twin turbo set-up. The SVTOA website has alot of good info on power adders for the cobras:

http://www.svtperformance.com/forums...splay.php?f=74

There are a few thing's you can do to get over 500rwhp without swapping the Eaton.Check out SVTPerformance like MachnJo said.

My plans are Twin turbos, but thats later. I was wondering what the SLP exhaust kit would do. (headers, x-pipe, mufflers) Also a intake plenum and throttle body.

anything you can do to help the cobra breathe better is going to net you some good gains. i would deffiently get a cold air intake, LT headers, catback, throttle body, and plenum and have the car retuned again. That may not sound like much but you can deffiently see 50+ at the wheels right there. cobras breathe through a straw from the factory.

gotta agree with mattj on this. Factory terminators gain bigtime off little things since the factory corked the intake and exhaust systems so much. I've seen things like a CAI netting 25rwhp and a x-pipe and cat back getting another 20 on top of that. Even TB's are worth it on a blower car. You can spin the stock Eaton blower for a good 17-19psi but by then the heat has become a problem. What I'd do is slap on a methanol injection kit and a 17psi pulley with a set of 55lb injectors and see what happens. The motor is solid so as long as it's not ticking you're ok.