All things considered, more inches is more power. More power is more heat. In the world of inline 6 engines, that is as true as ever. You can put split headers on a 235. They sound good. You can put 2 or 3 carbs on if you want. They look good. You can put a hot cam in a 235. It will make tuning a fun and everlasting project. A stock 261 will probably make more HP than any of the options listed above. And, you will still be able to drive it. Stock 216 90 @ 3300 RPM. Stock 235 Powerglide: 136 @ 4200 RPM( best of all years) And for the 261 150 gross hp at 4000rpm. So cubic inches still the best way to make power. There are ways to get power out of these engines. Most involve a lot of work. Many will make the engine suitable for "Track" only driving. Most will show small gains and higher RPM. These are torque motors. Not spinners. Clean, working mid-range power for work is what they do best.
