It is a 1976 or 1977 Rupp Nitro 440 or 340. I had a freind who had one of these things in the late 80's which I rode. It was very fast for the day (100mph across the lake on a 440). It has a Xennoa engine which was used in some Rupps and Chapparrals. They had the radiator and also had coolant pass through the aluminum extrusion in the front bumper. The stock clutch was an Arctic Cat hex shaft clutch. The 340 was rated at aprox. 70hp, the 440 was rated 80-90hp depending on if it was a 76 or 77.