To the absolute purist, the idea of dropping an oil burner in the engine compartment of America’s sports car is sacrilege. But if you think fun can only be had from high-octane gasoline at 6,500 rpm, you’re missing out on the glorious smoke-filled madness of diesel engines. However, they come with a unique set of pros and cons. On the one hand, diesel engines offer awesome low-end torque that gas engines can only dream of – unless you drop in a big blower. It also has industrial-grade reliability, the ability to turn heads as soon as you find the car, and ridiculously high fuel efficiency when you drive it comfortably. Needless to say, diesel engines also last longer than gas engines.
The cons are also overwhelming–literally. Dropping an iron block built for trucks into a car engineered for a light small block completely destroys the factory weight distribution, turning a precision corner carver into a nose-heavy straight-line freighter. If you’re considering a diesel swap for your Corvette, you often have to trade a crisp V8 soundtrack for a narrower powerband, possible custom fabrication to clear the steering shaft and firewall, and, of course, idle tractor clatter. It is a game of radical transaction, but there are only a few people who have mastered it.
Scott Ray’s off-road diesel C3
If you want to understand just how deep this rabbit hole goes, look no further than a spectacular and delightfully anarchic Corvette build crafted by 16-year-old Scott Ray of Kansas. In 2007, Scott was sick of his Corvette C3’s gasoline V8 dying on the way to school. Instead of moving to a more standard small block, he decided to go the diesel route, inspired by his father’s opinion about the strong efficiency of the 6.2-liter Duramax engine found in Chevrolet Suburbans. After doing some research, Scott realized that the 6.2-liter block would bolt directly onto the existing Corvette engine mount. He found a great donor Suburban for just $700, pulled the motor and its 4-speed transmission, replaced the Duramax main bearings, seals, and gaskets, and loaded the entire assembly into his 1980 C3.
To handle the gravel roads around his farm, he also installed a set of rugged all-terrain tires. The result was an unmistakable, high-clearance C3 that delivered good economy. It’s a famous example of sports car styling meeting agricultural needs, showing that a teenager with a barn and a donor truck could create a more reliable vehicle than even Detroit expected.
Mike Spank Spangler’s 350 Olds Diesel ‘Corvage.’
If you think diesel Corvettes are only good for straight-line farm roads, you haven’t seen a “Carveg.” The brainchild of famed LeMans road racer Mike “Spank” Spangler, this budget endurance machine completely overturns the idea that track cars need high rpm and high octane fuel. Spangler, known in 24 Hours of LeMans racing circles for building completely inappropriate vehicles like a Harley-Davidson swapped Prius, decided to build a diesel Corvette race car. They grabbed an ugly, obnoxious 1984 fourth-generation C4 Corvette and shoved a universally reviled, cheap Oldsmobile 350-cubic-inch diesel V8 engine into its engine compartment. These engines were notorious for blowing head bolts and collapsing injection systems in the late 1970s and early 80s. With a strong 3-speed automatic transmission, the powertrain was built to tackle many hours of tough track stunts.
The mechanical payoff was unrealistic. Almost completely repurposed to run on waste vegetable oil – French-fry grease drained from restaurant fryers – Spangler and his crew routinely raced Corvettes for up to 5 hours straight between fuel stops in California. Minimizing pit stops is the key to victory in endurance races, and while highly-tuned gas cars are forced to pit and refuel every two hours, Spangler’s comically underpowered 77-horsepower clatter box outclassed everyone on the track on French-fry oil.
Johnny Gilbert’s 3,500 HP Cummins Pro Mod Corvette
Let’s move away from backyard builds and into the absolute pinnacle of competitive drag racing – Johnny Gilbert’s wheelhouse. When Johnny – the founder of Stainless Diesel – decided to graduate to the ultra-competitive Pro Mod category, he picked up an iconic 1963 split-window Corvette rolling chassis and prepared to drop an engineering atom bomb under the hood – a dry sump, solid billet aluminum 6.7-liter Cummins inline-6 developed in collaboration with Wagler Competition Products.
The engine features a custom billet aluminum cylinder head, top fuel head studs, high pressure Iveco-based fuel injectors and a massive 98 mm stainless diesel turbocharger that delivers immense amounts of boost. This setup can produce an astonishing 3,500 horsepower. To avoid that kind of violence, it uses a low-profile aluminum oil pan for the dry sump system. Johnny won the car’s first event, the Outlaw Diesel Revenge Race at Indianapolis, using only 50% of the engine’s actual power. He later achieved a historic Pro Mod record by destroying Rockingham Dragway in 4.14 seconds and clocking 177.58 mph at the ⅛-mile finish line.
Ryan Milliken’s 3,000-horsepower Billet Cummins C7
If Johnny Gilbert opened the door to high-level diesel Corvette drag racing, Hardaway Performance’s Ryan Milliken closed it completely. Milliken took a sleek seventh-generation C7 Corvette built for Radial vs. the World ⅛-mile drag racing and loaded it with a billet-aluminum Cummins inline-6 – easily becoming one of the wildest Cummins swaps of all time.
The engine is assembled by Freedom Racing Engines using a Fleiss Performance Engineering block and a Wagler Competition Products cylinder head and rods, with a Harts turbocharger putting a nasty amount of boost down its throat along with a heavy dose of nitrous oxide from the nitrous outlet. Managing that raw mechanical aggression on small radial tires requires absolute wizardry. Controlled through an S&S setup, this diesel-burning C7 drag car accelerates to 60 feet in one second and covers ⅛ of a mile in 4.18 seconds.
Ryan Lusk’s 12-valve Cummins 6BT C3 Stingray
Ryan Lusk – a professional diesel mechanic and owner of Low Budget Diesel Performance in Mitchellville, Iowa – initially laughed off his father’s suggestion of installing a Cummins engine in the Corvette. But when someone said it couldn’t be done, he couldn’t resist the challenge. His 1968 C3 coupe was fitted with a 396 cubic inch big block V8 when the opportunity for a diesel swap arose.
It started with a real headache – squeezing a massive, massive 5.9-liter turbodiesel Cummins 12-valve inline-6 into the Corvette’s engine bay. Ryan completely cut out the floorboards, creating custom aluminum and steel panels to fit the big block precisely. He added a heavy-duty 47RH overdrive transmission fitted with a Goerend triple-billet torque converter to handle the massive low-end twisting forces. Running an S300 turbocharger and custom marine injectors, Ryan transformed the unloved, broken-down C3 into a dedicated drag car that won the NHRDA’s Pro Stock Diesel Championship two years in a row and rocketed around the track with a lap of 11.88 seconds at 129 mph, eventually setting a personal best of 11.32 seconds at 133 mph.
