Back in the mid-1960's there were a huge number of Chris-Craft wooden runabout boats on the lakes around Nashville. My father got quite a reputation for being the top tuner available to make those boats run well. The Hercules industrial engine was a flathead inline six, converted for marine use by Graymarine. If you think it's difficult to make a stovebolt a hotrod, try it on a side valve engine, sometimes one equipped with an updraft carburetor!
Dad would do all the "go fast" modifications the other boat wrench jockeys did, and then do one more thing- - - -have the tachometer recalibrated. It's amazing how much "faster" a boat feels like it's running when the tach is indicating 200 RPM faster than the crank is turning at full throttle!
LOL!
Jerry
