Dont know for sure? Always wondered what my 74 GPX had but the dealer could"nt say. I still have the original brochures from 73-74-75-77 that the dealers gave out. All the sleds showed the H.P. except the GPX and SRX? I love looking back at them from time to time and seeing how far they have evolved. Says here the 643 had a whopping 50 H.P. !!!!!!
My first sled was a 1973 GP 292 with big time H.P. of 27!