What Dave said. We have run both R-4s and Carbotechs in the back. Never had the issue with the Carbotech's swelling in the rear, and they used to give us a much more pronounced bite, but I think Carbotech may have changed the shoe. Doesn't seem the same. When you get the rears working right you should be blueing the drum friction surface. Definitely get two ducts up front and stay on top of your calipers. Ours had needed rebuilding about every 3 weekends. We run SRF fluid and bleed after every couple sessions on track. Brakes are by far the biggest maintenance issue on a Z.