305ci is not exactly a magical number when it comes to high performance engines in most people’s minds but the reality is that if you are a stock car racer or someone who has followed the history of the Trans-Am series, 305ci is an important number! Many classes in sportsman style stock car racing have a 305ci limit and Trans-Am had a 305ci limit for many, many years (heck, maybe it still does?).
The venerable 305ci Chevy engine was never built to be a performance runner out of the box. It was a base V8 engine that was supposed to be more economical than the 350 engine it was replacing and make adequate power to shove cars down the road. The LG4 and L69 models were the most common examples with one making about 150hp and the other making about 180. Along the way there were enhancements like TPI fuel injection and better cylinder heads. The browser always the big problem. Being a very small bore engine limited valve size and that fundamentally hampered the potential horsepower making abilities of the iron lump.
That being said, tens of thousands of stock car racers have beaten those little engines into steaming pulps over the years and they have the tricks to cheat them up into making decent, raceable horsepower. Being that many classes also have “claimer” rules on the engines, spending a lot of dough and going off the deep end is a dumb idea. (Not to say that people don’t do it!)
Lastly we have included the 305ci GMC V6 if for no other reason than out of respect. An engine solely built for torque and as a mover of things, it was not a performance engine and has literally no ability to ever be one. Heavy, strange, and low revving, it was the right mill for the time when developed and today they stand as interesting relics of the past.