LISTEN 09:20

If we were to say the name “Robert Glenn Johnson Jr” not many people, besides hardcore NASCAR fans, would know who we are talking about. However, mention the name Junior Johnson and “Mystery Motor” and nearly every NASCAR fan knows what we’re talking about. If you haven’t figured it out, Robert Glen Johnson Jr and Junior Johnson are the same person.

The Mystery Motor refers to Junior Johnson’s most famous car, which was a 1963 Chevy Impala SS with an extremely rare Mk II engine. This engine was a very limited production model that was wedged between the Mk I 438/409 engine and Mk IV 427 engine. This engine only saw roughly 50 total units produced, though some claim there were only 18 ever produced, making it one of the rarest GM engines ever built.

Shortly after these engines went out to various Chevrolet drivers, Chevy pulled the plug on its race sponsorship and the owners of the cars were stuck with modifying and fitting the engines themselves. Junior Johnson’s Mk II 427 wound up being the most powerful built at the time and resulted in a total of seven wins, nine pole positions, 13 top-5 finishes, and 14 top-10 finishes in just 33 races in the 1963 season. Its overall power and rarity earned it the name “Mystery Motor.”

Following the 1963 season, Chevy had began production of the Mk IV 427, rendering the Mystery Motor ineligible for NASCAR competition and reducing Johnson’s win total to less than half the following year.

If you have ever wanted to own a piece of automotive and NASCAR history, this is your chance, as RK Motors Charlotte has put Johnson’s 1963 Impala SS up for sale, Mystery Motor and all.

Click past the jump to read our full review.

  • 1963 Chevrolet Impala SS "Mystery Motor"
  • Year:
  • Make:
  • Model:
  • Engine:
  • Transmission:
    Four-speed manual
  • Horsepower @ RPM:
  • Energy:
  • Displacement:
    427 cubic inches
  • Top Speed:
    165 mph
  • car segment:
  • body style:


1963 Chevrolet Impala SS "Mystery Motor" Exterior
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After the 1963 racing season, Johnson’s `63 Impala SS was disqualified from NASCAR and simply disappeared into obscurity. The Impala SS Mystery Motor was eventually uncovered in a barn and found to be in impeccable condition for its age. Instead of restoring it into pristine condition, its owner wisely chose to keep it in its as-raced condition, something that few think to do.

1963 Chevrolet Impala SS "Mystery Motor" Exterior
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This 1963 Impala is draped in a coat of all-white paint with all of its original decals, including Johnson’s main sponsors Holly Farms Poultry and Chevrolet, though they pulled funding prior to the `63 season. As we said, this is not a pristine vehicle, as it is listed in “as-raced” condition, which means it also comes with all of the bumps, bruises, and imperfections that are gained during a racing season.

The great thing about NASCAR in the early years was the fact that the cars truly were stock cars. They are not like modern day stock cars where a metal body is crafted to somewhat resemble its factory counterpart. This is the real deal that actually rolled off of Chevy’s production line. It features the Impala’s signature grille and hood emblem, as well as the front bumper.

On the grille, you can actually see where the quad headlights originally were, but were removed and metal inserts put in their place, per NASCAR regulations. The front turn signals and factory chrome front bumper still remain on the car.

1963 Chevrolet Impala SS "Mystery Motor" Exterior
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The backside of the Impala received the same NASCAR treatment as the front, with the Impala’s signature six taillights removed and covered with metal. Besides the deleted taillights, the chrome rear bumper and Impala emblem still remain intact.

1963 Chevrolet Impala SS "Mystery Motor" Exterior
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From the looks of things, the body is relatively straight for being an ex-racecar and there is no visible rust. This is the type of car that you buy and store without doing anything else to it. Restoring it would likely lower its worth,so our hats go off to the owners for not doing so.


1963 Chevrolet Impala SS "Mystery Motor" Interior
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The inside of this Impala is very much a racecar from the `60s. You get a single bucket seat from the factory, not a racing seat. You get the standard massive all-black steering wheel and a series of racing gauges, including: tachometer, water temperature, oil pressure, oil temperature, amps, and fuel pressure.

1963 Chevrolet Impala SS "Mystery Motor" Interior
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Keeping things safe in a rollover crash is a multi-point roll cage. The rest of the interior is lined in what appears to be stainless steel, with the exception of the factory dashboard. However, where the gauges, climate control, and other dashboard-mounted controls would be are sheets of stainless steel.

Just like the exterior, the interior is 100 percent un-restored and in its original racing condition.

Engine and Drivetrain

1963 Chevrolet Impala SS "Mystery Motor" High Resolution Drivetrain
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Owning any car driven by the legendary Junior Johnson is awesome, but the rest all pale in comparison to this Impala SS. And the reason they do not compare is because of what is under that hood, the “Mystery Motor.” As we stated the Mystery Motor isn’t so much a mystery, as we know it is a limited production Mk II 427 cubic-inch V-8.

1963 Chevrolet Impala SS "Mystery Motor" Drivetrain
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This truly is a `tweener engine, as it features the same bore spacing – the distance between the centermost point of on cylinder to the next – as the Mk I 348/409, but has the same 4.31-inch bore and 3.65-inch stroke as the Z11 427 cubic-inch engine found in production 1963 Impalas. On top of all of that, the Mystery Motor features the same two-plane cylinder heads found on the “Porcupine” engines, the Mk IV engine. It really appears as if the MkII was Chevy’s own guinea pig engine.

All of this and a little bit of tuning pumped the 427 cubic-inch V-8 engine to a massive 600 to 650 horsepower, a full 173 to 223 horsepower more than the 427 was rated. This is what many people attributed Johnson’s 1963 success to, but they later found that his was a pretty good driver too. Back in `63 many racers often assumed Junior Johnson would either take 1st place or retire before the end, due to engine failure, as there were very few cars, if any, that could hang with the Impala’s 165 mph top speed.

The engine is about as original as possible, even the shiny valve cover paint is in its original racing condition. There are only two components that were replaced in this engine’s life; those are the alternator due to failure and the carburetor due to theft.

1963 Chevrolet Impala SS "Mystery Motor" Interior
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Backing up the Mystery Motor is a four-speed manual transmission. There is little mention of what transmission it is, but we venture to say it is the same transmission that came with the 1963 Impala SS.

Overall, the engine is a thing of beauty. The most impressive feat is 600 to 650 horsepower in a 1963 V-8 without modern day modifications. That is simply amazing and a tribute to what NASCAR once was.

Suspension and Braking

Unfortunately, there is no information given on the suspension and braking systems, but we would assume it to have the standard Impala SS suspension and brakes with some slight modifications.


This car is classified as a “Private Collection” in RK Motors Charlotte’s inventory system, so they do not list a price for it. A high end Impala SS with the 409 and a four-speed fetches about $62,725, but with the rarity and story behind this car, you can expect at least three times that value. We would venture to say that RK Motors Charlotte would part ways with this Impala for roughly $200,000.


1963 Chevrolet Impala SS "Mystery Motor" Exterior
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This car was driven by a Hall of Fame NASCAR driver and one of its all-time legends, and it features the storied Mystery Motor. There is no such car that could compete with this one-of-a-kind car.


1963 Chevrolet Impala SS "Mystery Motor" Exterior
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We absolutely love classic racecars and classic NASCAR stockcars really hold a special spot in our hearts. This was a time when NASCAR was a natural sport without its corporate mumbo jumbo, restrictor plates, and level playing field. It was a sport of who can build the biggest and baddest car within our limitations. This made it a sport of both science and skill, making it extremely intriguing.

This is a legend of that era, despite running only one season, and it is in its original racing condition. What is there not to like about it? Oh yeah, the undisclosed pricing. We assume that RK Motors is leaving off the pricing to see what exactly people are willing to give for it.

If you have an extra $200K lying around, we suggest offering it to the folks over at RK Motors. We bet they will hand over the keys and title to this legendary machine.

1963 Chevrolet Impala SS "Mystery Motor" Exterior
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  • Leave it
    • Not 100 percent original (carburetor and alternator)
    • Lacking a price tag is not a good thing
    • No description of its mechanical health
Justin Cupler
Justin Cupler
About the author

Press Release

Robert Glenn Johnson, Jr., better known as Junior Johnson is a name that needs little introduction to the racing community. A member of the Inaugural class of the NASCAR Hall of Fame, inducted on May 23, 2010, Junior Johnson was also named one of Nascar’s 50 Greatest Drivers in 1998. As a driver, Junior Johnson claimed 50 victories, the most ever for a driver that did not win a NASCAR points championship.

As a team owner, he worked with some of the legendary drivers in NASCAR history, including Darel Dieringer, LeeRoy Yarbrough, Cale Yarborough, Bobby Allison, Darrell Waltrip, Neil Bonnett, Terry Labonte, Geoffrey Bodine, Sterling Marlin, Jimmy Spencer, and Bill Elliott. In all, his drivers won 139 races, which is third only to Petty Enterprises and Hendrick Motorsports. His drivers won six Winston Cup Championships—three with Yarborough (1976–1978) and Waltrip (1981–82, 1985).

Behind the statistics and numbers, however, lies the real story of why Junior Johnson is a true legend of NASCAR and is loved by racing fans across generations. Named “The Last American Hero” by famed author Tom Wolfe in the March, 1965 issue of Esquire Magazine, Junior rose to prominence during the era of racing when guts and ingenuity determined the winners and losers, rather than who had the most money to spend. America fell in love with the automobile in the 1950’s and by the early 1960’s, all of the automakers had discovered that America loved going fast!

This 1963 Chevrolet Impala, which is owned by RK Motors Charlotte and maintained as part of our private collection, is THE legendary Ray Fox/Junior Johnson/Holly Farms #3 NASCAR which won seven Grand National Events in 1963, including the Charlotte, NC race held on 10/13/63.

During Junior Johnson’s miracle 1963 racing season, Johnson set a speed record at Daytona and led nearly every race during the season. He couldn’t be outrun and the other drivers could only hope that he dropped out of the race due to mechanical failures. The most amazing aspect of Johnson’s 1963 season was that Chevrolet pulled all of their money from racing sponsorships at the onset of the 1963 season. Ray Fox and Junior Johnson were forced to fabricate parts on their own and were able to compete and win against the factory sponsored Pontiac, Plymouth, Dodge and Ford teams.

There is much confusion and misinformation about the car which Junior ran in 1963. The car has been called a Z11, which it was not. It is a 1963 Chevrolet Impala Super Sport. What makes this car unique and explained its performance on the track is the incredibly rare RPO Z33 Mk II 427 “mystery motor”, supplied by Chevrolet. Designed by Richard L. Keinath, the Mk II was the missing link between Chevy’s Mk I 348/409 engine and the Mk IV 396 V-8 introduced in 1965. (The Mk III was an ultra-big-block project, stillborn.) The Mk II’s short-block used the same 4.84-inch bore spacing as the 348/409, and its 4.31-inch bore and 3.65-inch stroke were identical to those of the 427ci Z11 version of the 409. However, the cylinder heads employed valves canted in two planes, just like in the “porcupine” engines that would appear a few years later.

On January 21, 1963, barely days after Yunick and the other four Chevy factory-supported teams received their final engine packages and only a few weeks before Daytona, General Motors Chairman Fred Donner ordered all divisions to shut down their racing programs effective immediately. The Mk. II V-8 was marooned. Some sources say 42 engines were produced before the plug was pulled; others claim as few as 18.

Dyno test results on this engine show that is produced somewhere between 600-650 HP, which gave the Z33 powered Chevrolets a significant advantage over their competitors during the 1963 season.

The engine in this 1963 Chevrolet Impala is the exact same engine that was in the car at the close of the 1963 season. The engine and the car were banned from NASCAR before the onset of the 1964 season and the Impala disappeared into a barn.

This Impala is in “as-raced in 1963” condition and has received no modifications since 1963, other than a replacement alternator and carburetor (the original Holley was stolen).

RK Motors Charlotte is honored to be the custodian of the vital piece of racing history and plans to do a complete analysis of the car over the coming months, as we analyze, with the assistance of Junior Johnson himself, exactly how a NASCAR was prepped and campaigned during the early years of the sport.

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Show Comments


  (1) posted on 10.30.2015

The car is currently displayed at The Simeone Foundation Museum in Philadelphia. An amazing piece of American Race history reflected both in the 63 Chevy body and the winning 427.

  (419) posted on 06.14.2012

It’s good for those who wanted to covet in before; Chevy, once again, gives you a chance.

  (676) posted on 06.7.2012

I’m just not a fan of vintage re-launches, and that’s why I can’t seem to like it even if its engine got better.

  (458) posted on 05.27.2012

It may have been modified now to be fit to compete with the latest automotive, but I doubt its figure is as stable as before.

  (569) posted on 05.24.2012

It probably isn’t worth it as it has been implied that it was left untouched. The only fact that it can boost of is that it was a top performer of its era, but then again, what about now?

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