An initialism for the Royal Automobile Club, a British motoring organization known for providing roadside assistance, vehicle recovery, and historic technical standards. In classic car contexts, it is frequently referenced regarding the RAC horsepower rating, an early formula used for taxation purposes based on cylinder bore rather than actual engine output.
Heard on the job
The old registration documents list the engine at 12 RAC horsepower, even though it makes about forty on the dyno.
Insider tip
The RAC horsepower formula severely penalized large-bore engines, which is why early British engines often featured long strokes and narrow cylinders.