The HM Series is designed for big displacement race engines. At 45mm bore and 42mm Venturi, the HM carburetors are the largest in the Tillotson catalog. We do not recommend these carburetors for anyone less than the expert carburetor and engine builders. Because there is no specific engine, they have been designed to benefit from blueprinting for your specific engine and class truly. Look at our dominator section for built HM carburetor or contact use for your build.