In my accumulation of vintage Hot Rod mags, there are many articles reporting engine builds where they install various speed equipment and then do dyno tests (just like they still do today). Every one of these old tests done on the 216, 235 and 261 Chevy inline six reports the highest single HP *bolt-on* gain resulted from installing dual carbs (no 4-barrels back then). But...Torque isn't helped much, and the HP gains seem to be in the higher RPM ranges. Next biggest increase comes from bumping up the compression, either by milling the head or pop-up pistons - and that DOES increase torque throughout the RPM range. Some cam grinds show similar improvement but others actually hurt output...dual exhausts (Fenton or split manifold) usually didn't raise the numbers much, but probably helped bump the output with dual carbs. So much for bolt on mods. The most dramatic increase, by far, was by increasing cubic inches. This always resulted in a healthy increase in both torque and HP over the entire powerband. Conclusions? Improving the breathing of a 235 should be addressed first...and start with a 261 if possible.
