Whats the deal with 340s?

340s were all performance engines. Until the magnum came out there was not much in the way of factory performance 360s.

In my opinion the biggest advantage the 340 had was by average Joe hot rudders who would either build a basically stock short block with stock replacement pistons. Cylinder heads were basically stockers most of the time. The most porting a set of heads got was a gasket match. Guys would throw cam of there choice and hit the streets. Most mods were bolt ons. Different carb and intake. 360 ran well but couldn't hold a candle to a 340 in this state of tune.

Today there are more piston choices. People almost never install stock pistons in a performance build. Head choices are out there now. You don't have to hope you come across a set of x heads. Magnum parts open it up further.
The performance gap has closed if not completely eliminated.
I still love 340s though.