Ackerman angle is a function of toein/out and steering arm length, the arm length is usually fixed (unless you are making your own parts???) and the ackerman angle will then be dictated by whether you want/need to run toe in or toe out...

This is assuming you are using a normal rack and are not moving it too?!?!?!?! A quick rack will make no difference but a rack with a different throw will, also if the rack is re-positioned it can affect the throw that the steering arms see.