General Motors began flirting with turbochargers on production cars as far back as the early 1960s. The first model, the spectacularly named Jetfire from Oldsmobile, was a regular Cutlass fitted with the even better named “Turbo-Rocket” engine.

This 3.5 litre V8 featured a Garrett T5 turbo running 5 psi of boost that put out 215 hp and 300 lb ft of torque, a respectable increase over the standard engine but there was an issue: in order to achieve boost the Jetfire needed to have its “Turbo-Rocket Fluid” (that’s not a joke by the way) tank full. This fluid was a mix of methyl alcohol and water which was sprayed into the intake to keep combustion temperatures down. 

Needless to say, owners forgot to fill this tank and the car would cut boost and thus performance. Due to complaints from owners and the complexity of the Jetfire’s powertrain, production ended in 1963 with just 9,607 built.

Oldsmobile Jetfire Advert via Amazon Media

Around the same time, GM developed a turbocharged engine for the Chevrolet Corvair but unlike the Turbo-Rocket, the Corvair’s powerplant was a 2.4 litre flat 6. A number of upgrades were made to the internals and a different turbo made by the Thompson Valve Division of Thompson-Ramo-Wooldridge was fitted. Performance figures came in at 150 hp and 210 lb ft of torque, an impressive increase of 47% and 58% over the regular naturally aspirated car. 

Although this engine didn’t need any special fluid to run, it was plagued with another issue: lag. Lots and lots of lag. Contemporary road tests claimed the turbo Corvair took “4.5 to 5.0 seconds for the turbo to reach full boost”. As you can imagine, this lag wasn’t popular with customers but even so the turbo Corvair limped on until the end of the 1960s. The car saw some in-life revisions but ultimately the market gravitated towards large displacement performance cars and turbocharging fell out of favour.

Fast forward to 1978 and the world was a different place. The fuel crisis had decimated the performance car market and the Malaise era was in full swing thanks to 1975’s CAFE (Corporate average fuel economy) legislation. Through some miracle Chevrolet’s C3 Corvette had managed to survive, albeit with a range of engines that were strangled by legislation. Turbocharging once again came back into focus with Corvette’s in-house research team looking into the viability of a forced-induction engine.

Chevrolet engineers Jim Ingles and Gib Hufstader worked on a blow through turbo system that fed boost directly into the carburettor of the L48 engine. A Phase I Turbo car was built to test the system's viability for production. Allegedly this car was an animal and offered performance well beyond the standard car, beating it by over 2 seconds in the ¼ mile. Unfortunately the blow through system proved to be unreliable and downright dangerous, with the Phase I car burning to the ground in testing.

Phase I Turbo Corvette prototype - source Motortrend

Phase II Turbo Corvette prototype - source Hearst

Undeterred by the fiery death of the Phase I prototype, a follow up Phase II car was built with an L82 engine. This car featured upgraded Delco electronics and a knock sensor to better monitor the engine’s performance. Combined with chassis upgrades and a beefier transmission, this car represented a more complete design. Phase II was handed out to magazines for their evaluation, with Car and Driver stating that “On the street it's a silver bolt of lightning waiting for your foot to say when to strike.” A glowing review for what was a skunkworks project.

A Phase III car was developed, utilising aluminium cylinder heads and other lightweight parts designed to offset the weight of the turbo system. Paired with a very 70s white and blue colour scheme, this car showed execs what a production-ready turbocharged Corvette would look like. However, just like in the late 60s, the cost of the package and the complexity of the turbo engines ultimately lead to turbocharging once again taking a back seat. A quote from the Chief Corvette Engineer at the time - Dave McLellan - is perhaps the best way to close this chapter: “These cars were, however, great fun to drive while the fuel lasted and the engine held together. These were definitely not cars that could be turned loose in the hands of a customer. Nor did we have any hope of selling them as emission-certified automobiles.”

Phase III Turbo Corvette prototype - source Motortrend

When the fourth generation C4 Corvette was unveiled in 1983 it signalled a new direction for the model, with more impressive engineering and futuristic boxy styling. Its powerplant was still the ever popular small block V8, this time being the L83 variant that developed 205 bhp and 290 lb ft. McLellan and his team had been investigating a 400 bhp package for the car to give it the performance it deserved. Working with Chevrolet’s prototype car builder Specialized Vehicles Incorporated (SVI), their first experiment was a turbocharged V6 which proved to be an underwhelming unit that didn’t perform as well as the upcoming L98 and offered unacceptable levels of noise, vibration and harshness.

SVI’s next project was to build a twin turbo V8 Corvette. Previously it was thought that a twin turbo engine wouldn’t fit under the bonnet but SVI were confident that this could be achieved. SVI went on to build 14 twin turbo C4s that were submitted to GM for testing and validation. SVI’s work was impressive with engines producing 440 bhp and 570 lb ft of torque, using sophisticated mirror image turbos from Mitsubishi and an air to air intercooler. But as always seemed to be the way, a change of focus within GM put a hard stop on development. GM Vice President Lloyd Reuss vetoed the idea of turbocharging saying that “a turbocharged, pushrod V8 would be perceived as low tech by potential buyers”, and instead pushed for a dual overhead cam engine which morphed into the ZR1 project.

So what became of the turbo C4s I hear you ask? They ultimately served as development mules for the ZR1 project and occasionally did promotional events for Chevrolet. All was not lost however, as the appetite for a turbocharged C4 was still there but GM didn’t want to develop the system in house. Enter: Callaway, the brand that had made a name for themselves offering turbo kits to all manner of European cars in the late 1970s and early 80s. GM had sent them one of SVI’s mules and asked them to make a production ready kit that would not interfere with the emissions systems.

1984 fourth-generation C4 Corvette - source

SVI Turbo C4 Corvette engine bay - source Amazon Media

Callaway Corvette - source Callaway Cars

Callaway Corvette - source Car Scoops

Callaway duly delivered and in 1987, option code B2K could be ordered directly from Chevrolet when you specified your Corvette. For the cost of $19,995 your car came with 345 bhp and 465 lb ft of torque and a top speed of 178 mph. Did I also mention the 12,000 mile 1 year warranty too? Over 500 B2K cars were built by Callaway from 1987-1991 and at the end of production the upgrade cost had risen to $33,000 but the performance had too, with 403 bhp and 575 lb ft of torque; 20 bhp and a humongous 205 lb ft more than the ZR1.

Now, I can't talk about Callaway and Corvette without mentioning the Sledgehammer. No, not a builder's best friend but an infamous record setter. 880 hp, 772 lb ft, 255 mph. That’s all that needs to be said. It was a moment of madness and I urge you all to go and watch the fantastic “Project Sledgehammer” documentary on Callaway’s YouTube Channel. I’m saving the full details on this one for a future dedicated Short Shift…

For 1992 the LT-1 engine replaced the L98 and this marked the end of the option code B2K, there wouldn’t be another factory backed turbocharged Corvette until the 2025 ZR-1. Although the CERV III prototype showed the world what a mid engine turbocharged “Corvette” would look like, it took two decades before it became a reality. I’m glad it's here, but what took you so long GM?

Corvette CERV III fully functioning prototype - source Motortrend