Here is an interesting video citing 8 muscle cars whose horsepower was deliberately under-rated by the factories to get a competitive edge at the track and, also, to keep insurance premiums down. Two Mopar cars stand out- a 1970 Hemi 'Cuda (425 hp. to 470 hp.) and a 1970 Challenger R/T 440 Six-Pack (390 hp. to 430 hp.).