Callies Ultra Xd Stroker Connecting Rod Design offers greater cam to connecting rod clearance. This innovation will allow the use of increased base circle cams for improved valve train performance, stability, and horsepower. For the first time engine builders are given greater flexibility in selecting valve train components when using a standard cam height block. The Ultra Xd concept has been track tested and proven to be a reliable, long term solution to troublesome connecting rod to camshaft interference problems. Ultra Xd connecting rods are available in I-beam or H-beam for the SBC, BBC, and LS Engine Families.