When is a monkey bike not a monkey bike? When you stuff a four-cylinder engine into the chassis, that’s when?

Among all the other craziness that was sold at last month’s Mecum motorcycle auction, we happened to miss this one-off custom in the listings (you can forgive us—there wasa lot to see, and the auctionbrought in $22 million). According to the Mecum website, it’s a “1973 Honda 4-Cylinder Mini Trail Pit Bike,” but in reality, it’s a Frankensteinian creation that looks dangerous, and really, really fun.

The base machine here is a Honda Z50 Trail, says the auction listing. Now, this is the part of the story where the moto-savants sigh, push their glasses up their nose, flex their knuckles and launch attacks via the comments section, keyboard rattling with the staccato precision of an MG-42: “It’s OBVIOUSLY a 1961 Z100 with a blah blah blah, and you can tell by the blah blah blah.” Gentlemen, we get it: You wanted one when you were 8. Let us suffice to say that it’s a monkey bike, made for goofy fun, and by necessity, under-powered. Too much jam, and the weedy chassis and chunky tires will get you in trouble.

Nevertheless, a bold man, a man with little care for the conventions of standard monkey bike fun, took this minibike andstuffed a four-cylinder engine into the frame. Boris “Bob” Guynes repurposed a Honda CB350 Super Sport engine for this project. So, it’s not the most exciting four-cyl that you can get your hands on, particularly because it’s been choked-down with a dual-carb setup. Still, it’s a big upgrade from the original small-bore single that this bike would have had.

Here’s what the Mecum listing said about the custom:

Output of the far-from-stock engine here is unknown, but Boris “Bob” Guynes was well-known for his ability to get the most out of any Honda powerplant. Dual carburetors on a one-of-a-kind, hand-fabricated intake complete with not one but two strategically placed U.S. quarter-dollar coins replace the factory four-in-a-row setup. A Z50 seat and fuel tank, rare Tomaselli Cross handlebars, four-into-two exhaust and an adjustable-height center stand finish out the hot setup. The pit bike is not intended for use on public roads, but it could theoretically be registered with the addition of a battery, lights and turn signal from a street-legal Z50. This monster minibike still needs some sorting, but it is an excellent opportunity for a new owner with the vision and bravery to finish the job.

The Mecum page doesn’t list the sell price, but this did sell, and we’re sure the happy buyer is already pulling dank whoolies up and down the street, spitting flames everywhere from those shorty pipes, and generally riding this thing the way it was intended to be flogged. At least, we hope so.