How wide can i go in the rear with 18's and a a little lower ride hight?

 

That is a pretty open ended question...how much work are you willing to do to make things fit? And do you want wide wheels but don't mind running skinny tires? Or do you want the widest you can go running proper meaty tires?

 

Ok.... well i am trying to leave the body as stock looking as possible as far as the body lines but i need more tire to hold about 400hp

 

Rolling the fenders will allow you to go with about a 20mm wider tire in back than you would stock. So maybe 275 width on a 9.5" wide rim? If you can find proper (stock) offsets, this should work fine with just a fender roll.

Unlike others only concerned with looks, I would avoid excessive negative camber at all costs. Start dialing in huge camber and you're going to have a hard time putting down all of that power.

 

You can fit a 285/30 with the right wheel. You are probably going to have to go with CCW or something like that though, not many wheels are available off the shelf in sizes ~10.5" +75.

 

There comes a point where wider tires and wheels are more about looks than performance. Unless the car is running more horsepower I don't see anything wider than the 265/35R18.