Because they were big heave under powered slug motors. I had a biddy with a 6o something GMC 3/4 ton with one in it and it sucked. We swapped in a Chev 350....much better thank you LOL
no not really thats a 305 probably, whuch put down 150-165 gross hp and 260-280 gross torques, if its not the 305 then maybe it would have a little more, here a sight about them. http://www.6066gmcguy.org/EngineData.htm