Cool Car TV / YouTube There are semi trucks, and then there's Thor24. It doesn't exist in any brochure or catalog, since it's a completely custom project wrapped around the stretched chassis of a 1979 Peterbilt 359 — one of the many semi-truck brands now owned by Paccar. Motivating this behemoth is a unique V24 engine built out of two now phased-out two-stroke Detroit Diesel V12s connected by a splined crankshaft and featuring no fewer than 12 superchargers for almost 4,000 horsepower. A 44-foot long, 32,000-pound semi truck with a top speed of 130 mph sure takes some planning and building, and Thor24's creator, Mike Harrah, reportedly spent 7 years and a claimed $7 million putting this thing together. A huge figure for a semi truck, but as it turns out, actually quite a wise investment. When Thor24 crossed the auction block in 2019 at a Worldwide Auctioneers event in Riyadh, Saudi Arabia, it managed to attract a record-breaking $12 million. That remarkable result cemented it into history as the most expensive semi truck in the world. But despite the auction's location, the truck never left town and remained in Arizona where it was built. The engineering behind Thor24 Cool Car TV / YouTube There is much to admire about Thor24, but its drivetrain is a primary source of intrigue. Mike Harrah began with two 13.9-liter Detroit Diesel V12 engines, which in standard trim kicked out around 475 horsepower, and connected them end-on-end with a splined crankshaft. The result was a 27.9-liter V24 engine that hooked up to an Allison HT740 transmission. Harrah then wanted forced induction to play a major role in Thor24's powertrain, so a total of 12 Detroit 6-71 superchargers were added into the mix, along with eight nitrous-oxide bottles, slotted between the engine banks. A recipe that would leave most in awe, even more so when they read the claimed output is a dizzying 3,974 hp. Despite tipping the scales at 32,000 pounds, the truck can reach 130 mph. That is an impressive feat for any truck, let alone a custom rig with these proportions. Of course, there are some serious forces involved in stopping a 130-mph, 32,000-pound semi-truck. To help the brakes out, Harrah equipped his creation with four 12-foot drag parachutes –sort of like the Dodge SRT Demon 170's parachute system. Its underbody is as astonishing as the rest of the build, thanks to chrome plating, polished aluminum, and stainless steel details. Thor24's usability drives its value Cool Car TV / YouTube It would be a mistake to assume Thor24's value stems solely from horsepower figures and shiny underside components, though. There is a world of extensive custom fabrication to see throughout the cab, too. For starters, the original Peterbilt cab was stretched to accommodate an extra pair of doors, and a Lamborghini-style scissor operation was incorporated for the passenger front door. Stepping inside, a smattering of gauges steal the eye, 24 in total, with a custom broadsword-esque shifter center-stage. In terms of infotainment, Thor24 puts Apple CarPlay to shame, boasting seven movie screens and a 1,500-watt-per-channel 110-volt audio system. It would make quite the static crowd-pleaser, but Thor24 was never designed to be a one-trick pony. It still boasts all the gear necessary to tow a full-size trailer. The attention to detail and refusal to compromise explain how this truck managed to attract an eight-figure auction result, and the fact that it's genuinely usable and not just a showpiece helps boost its appeal even further.