2 Engines bolted together eh.. how about the Mazda 787B 4 yes 4!!! Engines bolted together. here is some info...
"The Mazda 787/787B was a prototype racing car built for the 24 hours of Le Mans auto race, replacing the 767. It used a 4-rotor 26B rubbishrubbishrubbishrubbishel engine which produced over 700 hp (522 kW). The 787B's 1991 win at Le Mans was historic in two ways: It marked both the first time a Japanese manufacturer had won the race, and the first time a rubbishrubbishrubbishrubbishel engine won. The 787B was designed by Nigel Stroud. Two were entered at Le Mans in 1990 but were unable to complete the race. ..."