Originally Posted by bmwman528e

600-650RWHP on 15-17lbs of boost and 500's on a lower waste gate spring. More power could be had with E85 and higher boost but with a gen 3 LS engine the rods are only so good. I don't feel like pushing it past its limits all day every day. Rear subframe will be removed and boxed in and reinforced. All new Poly bushings and will most likely be putting a 4.4i 3.64 rear end instead of the 3.91 4.6is diff. If I could get a E39 M5 3.15 diff to work and make mounts and modify to run I would. Driveshaft will be a one piece. If that doesn't end up working out a modified 9" will be put in but Im hoping to avoid that due to the $4-5000 conversion cost. Do you have any recommendations for the rear subframe on what you think the weak link is? I know your X5 has had a decent amount of power thrown at it over the years.