Chevroletis very much a mass-market brand. Even so, it'll occasionally throw out unicorns. One of those unicorns is the engine we're going to talk about here. A relative handful of these engines were ever made, and they gained a reputation for being absolute monsters. This super-rare engine is a key component of one of Chevrolet's rarest Muscle Cars. That super-rare muscle car is the Impala Z11, and it's a car that's infamous among muscle car enthusiasts! The 1963 Chevrolet Impala Z11 Is A One-Year Only Special Designed For Motorsports MecumWhen it comes to classic Chevrolets, the Impala Z11 is a true holy grail car. It was designed for motorsports, specifically drag racing and stock car racing. It retains the classy and understated look of the stock 1963 Impala, but under the skin it's something very special. It has a huge, powerful V8 engine (you'll learn more about that later), a close-ratio 4-speed manual transmission. To handle the extra power, it's got a reinforced chassis and heavy-duty suspension. It's also much lighter than a regular Impala, thanks to all non-essential equipment being stripped out (it doesn't even have sound deadening or a radio) and aluminum being extensively used in its construction (the hood, fenders and bumpers are all aluminum).The result of that huge engine, that racier transmission and those weight-saving modifications created a car that could complete a 1/4 mile in the higher end of the 10-second range. That's very impressive for a car from the early 1960s!Exactly how rare is the Impala Z11? Well, it was only produced for the 1963 model year. During that model year, only 57 of them were ever made. This genuinely makes it one of the rarest Chevrolets ever produced. It Has The Super-Rare Mystery Mark II Engine MecumYou might have been wondering exactly what the super-rare engine that powers the Z11 is. Perhaps fittingly for how rare it is, it's called the Mystery Mark II! It's a proper big-block 7-liter V8, producing a claimed 430 hp and 575 lb-ft of torque. That power rating is generally thought to be a conservative one. People have claimed that the Mystery Mark II actually produces over 500 hp! That would make its crazy performance for its time make total sense. The Mystery Mark II was based on the earlier 409 cubic inch (6.7-liter) W-Series engine. But, the original W-Series design was heavily modified to make the Mystery Mark II the monster it became. The deck height was raised, it was given a forged steel crankshaft and aluminum cylider heads with oversized ports and the compression ratio was increased to a very racy 13.5:1.As the Impala Z11 was the only car ever made to use the Mystery Mark II engine, that means the number produced is exactly the same as the number of Impala Z11's that were ever built. This makes it possibly one of the rarest muscle car engines ever built, period. While there are muscle cars that are rarer than the Impala Z11, they typically used engines that were also used in other models. The Mystery Mark II being exclusive to the Impala Z11 was actually quite a rare thing to happen for '60s muscle cars. As a result, the engine itself has as much of a legendary reputation as the car it powers! The Impala Z11 Is A Proper Collector's Car That Sells For Big Prices MecumBecause the Impala Z11 is such a unicorn of a car, it's not surprising that when they do appear on the used market they sell for massive amounts of money. As just one example, one Z11 sold for $298,000 in 2023. That's a lot more than the $60,879 average value across all versions of the 1963 Impala. Even the best examples of the more normal Impala SS performance variant rarely ever hit prices higher than $80,000. If you're lucky enough to be able to afford to have an Impala Z11, you've managed to bag yourself a super collectable car that could have a 7-figure valuation in due time! Other Super-Rare Chevrolet Engines That Were Put In Production Cars via Bring A Trailer The Mystery Mark II may be the rarest engine Chevrolet ever put in a production car. But, it isn't the only big-block monster that you'll only see a relative handful of show up! Chevrolet produced quite a few engines like these back in the golden era of American V8 power, and they typically ended up powering some of the brand's most special vehicles. COPO 427 Iron Block V8 via MecumThe clue as to why the COPO 427 Iron Block is so rare is in its name. This was an engine that only appeared in COPO specials. This included the Yenko Camaro, the COPO Chevelle and the COPO Nova. Because this engine was exclusive to those crazy COPO specials, it's estimated that less than 1,400 Iron Block 427s were built. That easily makes it one of the rarest big-block V8s ever made, even though it powered multiple different vehicles! L88 427 V8 MecumThe L88 engine is a big-block V8 that was put into a car that doesn't normally get associated with big-block engines. That's the Chevrolet Corvette, specifically the L88 model that was made from 1967-1969. L88 Corvettes were intended to be used for racing, and that explains its crazy power figures. It was rated at 430 hp, but many think its true output could be as high as 550 hp. ZL1 427 V8 Bring A TrailerThe all-aluminum ZL1 engine has to be one of the most infamous Chevrolet engines of all time. Only 71 of them were ever produced, with all but two of them being put into examples of the Chevrolet Camaro ZL1. This car ended up becoming one of the best muscle cars ever made, and is now an incredibly desirable collector's piece.Like the Mystery Mark II, the ZL1 was originally designed to be a racing engine. It's also got the same kind of huge discrepancy between the output Chevrolet claimed it had versus what people think it actually has. While Chevy claimed 430 hp, it's believed that the true figure is as much as 560 hp. That makes the ZL1 engine an absolute beast for its time!Sources: Bring A Trailer, Chevrolet, Classic.com
