BTR Brian Tooley Racing LS Piston Ring Compressor Tool 4.000 bore Fits 4.00" Bore 6.0 LS2 LQ4 LQ9 L76 L77 L96 L98 and more 4.00" bore engines. One piece aluminum tapered ring compressors have been around for some time, but BTR has made a significant improvement to the design. Rather than relying on the piston skirt to locate the pistons as theyre being inserted into the block like one piece tapered ring compressors currently on the market, the new BTR ring compressors have a small but very important reverse chamfer at the bottom that fits into the chamfer at the top of the block which serves two functions. First, it locates the ring compressor exactly over the center of the hole. And, secondly, it reduces the chance of the oil ring getting caught between the ring compressor and the top of the block. The lazer etching on a black background is easy to read and looks good even after lots of uses. In our beta testing against competitors tapered ring compressors, the BTR was easier to use and never caught a oil ring between the compressor and the block.