The 305 has sort of a horsepower cap due to the lowsy heads these motors have and the fact that you can't use any other heads on them. Car Craft magazine did a test on the 305 years ago to see exactly what kind of gains could be achieved. They did all that could be done with the heads(ported, polished, flow tested,etc.), they tried several camshaft, intake, carburator, exhaust and ignition combo's from mild to wild. The best they could do was somewhere around 315 horsepower. Thats not bad, but for all they had to do...... In my opinion the 305 was the biggest slap in the face Chevrolet ever gave it's performance customers and fans. You can make one run somewhat good, but don't get any high hopes. I bought a 75 Camaro and the previous owner installed a 305 in it. I put a 30/30 Duntov cam in and it ran better(pulled harder on the top end with out hurting the low end), later on I replaced the 2 barrel with a Performer intake and a Q-jet, also installed headers and a full exhaust. It was a big improvement over stock. One thing to make sure of, keep the exhaust not so high flowing, temporarily I had to use header mufflers on it and it ran like a dog. I didn't mean to dog out your motor or anything, but if your gonna mess with it put one in worth messing with, they all look the same from the outside.