The Past, Present, And Potential Future Of The LT5 Engine

LT5leadIn a move that’s been literally decades in the making, it looks like the Corvette may finally be going mid-engined when the eighth generation sports car debuts, presumably as a 2019 or 2020 model. With Chevrolet recently putting a hold on all factory tours for the next 18 months starting June and numerous spy shots surfacing that show Chevrolet testing a prototype that clearly has its power plant mounted mid-ship, the likelihood of this long-rumored change in design strategy only grows stronger by the day.

But what will power such a radical departure from the established Corvette playbook? Evidence suggests that Chevrolet may offer a V8 that ditches the pushrod-based design of the LT1 and LT4 motors in favor of a new dual overhead cam design not unlike the configuration found in Ford’s Modular V8 motors like the 5.2-liter “Voodoo” power plant that’s used in the Mustang GT350R – though whether it might get a flat-plane crank like Ford’s 5.2 is still anyone’s guess.

2016-05-19_00-00-48

This rendering applied to the C7 Z06’s aesthetic gives us a sense of the proportions that a mid-engine Corvette would have once it reaches its final production design.

While these allegations might sound outlandish they’re far from unprecedented, particularly in regards to the engine that might power such a Corvette, as the C4 ZR1 broke with the pushrod tradition all the way back in 1990. Here we’ll take a look at that power plant – the first generation LT5 – and consider what a presumed revival of the name might mean for the future of the Corvette.

The Original LT5

A few years after the introduction of the C4 Corvette, General Motors acquired Lotus. The English engineering firm was already a well-established performance house by that time, known for their long history in motorsport and limited-production, road going sports cars. In 1985, Chevrolet’s brass came to Lotus engineers with an ambitious proposal, asking them to help the Chevy engineers design and build the world’s fastest production car using the C4 Corvette as the platform – the model which would become the 1990 Corvette ZR-1.

Although the 1980s weren't exactly a legendary period for factory-produced performance, things were really starting to look up toward the end of the decade. By 1990 Chevrolet had unleashed the Corvette ZR-1 on the world. Equipped with new braking and steering systems unique to the ZR-1 as well as a new adjustable active suspension system FX3 that used tooling from the Porsche 959 supercar program, the ZR-1 was far from a one-trick pony. Of course straight-line grunt was obligatory though, and to get the supercar-caliber output Chevrolet wanted, they tapped Lotus Engineering to develop a bespoke DOHC V8 for the car. Images: General Motors

Russ Gee, Director of Powertrain Engineering for General Motors at the time, had toyed with the idea of turbocharging a V6 or a V8 for use in the new King of the Hill Corvette, but concerns over cost and reliability kept those options out of the running.

Of course the standard tune-port injected, 240 horsepower 350ci L98 that powered the C4 Corvette at the time wasn’t going to cut it for such and ambitious project, and rather than attempting to extensively overhaul the mill for ZR-1 duty, Gee turned to Lotus engineer Tony Rudd for assistance.

LT5

When it became clear that extensively overhauling the L98 V8 wasn’t going to get Chevrolet where they wanted output-wise and development programs that experimented with turbocharged power plants failed to pan out, engineers turned their attention to a 4.0-liter DOHC V8 that Lotus had been working on to serve as a template for the LT5. Image: General Motors

A year prior while on a visit to Detroit, Rudd had described a dual overhead cam 4.0-liter V8 that Lotus was in the midst of developing that produced 350 horsepower. Initially Gee had hoped that Lotus could design a set of heads that could be accepted by the traditional Chevy 350, but it quickly became clear that an all-new block would need to be developed to work with the Lotus cylinder head design.

The result of their efforts was the then-new LT5 engine. A far cry from the cam-in-block design of the L98, this all-aluminum, 32 valve motor featured four overhead camshafts in total and a unique air management system that could shut off or engage some of the motor’s intake runners and fuel injectors to allow the motor to remain in compliance with government fuel economy standards while delivering a then-unheard of 375 horsepower and 370 pound-feet of torque.

The 5.7-liter LT5’s design differed so dramatically from the L98’s that Chevrolet would outsource the assembly of the motor to Mercury Marine in Stillwater, Oklahoma, who would then ship the motors to GM’s Bowling Green, Kentucky factory for installation in the car.

1991-LT5

At 5.7 liters, the LT5’s displacement is one of the very few things it shared with the Corvette’s traditional pushrod 350 V8. Image: General Motors

The motor’s performance made it well worth the efforts, though, as the ZR-1 would sprint to 60 mph in just 4.4 seconds on its way to a top speed of 180 miles per hour – almost unheard of performance figures in 1990. The ZR-1 and its LT5 power plant would remain in production through 1995, with the latter seeing tweaks in 1993 to bump its output to 405 horsepower and 385 pound-feet of torque.

Mid-Engine C8 Rumors

Though speculation about a forthcoming mid-engined Corvette has been swirling around performance circles since the 1960s, a few years ago the rumors started getting too frequent to ignore, and when spy photos of heavily camouflaged GM two-door test mules that sported an unusual but tell-tale mid-engine chassis design started popping up on a fairly regular basis, it began to look like Chevrolet would finally be taking the layout of the eight generation Corvette production car where it had never been before.

Image: Autocar UK

Spy shots of cold weather testing like this only adds to the mounting evidence that this car is destined for mass production. Image: Autocar UK

With the naturally aspired LT1 and supercharged LT4 V8s being recent additions to the GM engine roster, introduced with the 2014 Stingray and 2015 Z06 respectively, many assumed that updated versions of one or both of these engines would find a home in the engine bay of the upcoming C8. But it appears that General Motors may have another surprise in store for Corvette fans in this regard as well.

What We Know So Far About The New LT5

The first indication that Chevrolet had possible intentions of reviving the LT5 moniker date as far back as April 2013, when it was discovered that they’d applied for a trademark for the name.

Adding credence to prospect of a new LT5 engine was a GM service department document detailing the internal codes the company will use for its 2018 model year vehicles that was found buried deep within the General Motors website in December of last year, a page which has long since been removed from the site by the company.

Image: Reddit

This screenshot from the GM web page that’s since been taken offline offers a lot of interesting information. Of particular note is the combination of the LT5 engine desitnation and its association with the Y book code, which denotes the Corvette platform, though it is not included in the engine types destined for 2018 production. Image: Autoblog

The information not only included LT5 as a new engine code, it also included descriptors that included 6.2L, DOHC, VVT, and ALUM, which can lead one to believe that a 6.2-liter, dual overhead cam aluminum power plant with variable valve timing dubbed the LT5 may be destined for production in the near future.

Without a mention of forced induction it seems unlikely this motor is destined for the upcoming C7 ZR1, as the ZR1’s output will likely be above that of the current 650 hp Z06, and getting 700+ horsepower out of a naturally aspirated DOHC V8 would likely be prohibitively difficult in terms of fuel efficiency, emissions, and cost.

Both the LT1 and LT4, seen here respectively, are relative newcomers to the General Motors engine lineup. While the naturally aspirated LT1 offers plenty of grunt and efficiency while the supercharged LT4 boasts 650 horsepower and an equal number of foot-pounds of torque, that doesn't mean there isn't room for a DOHC engine in the family. Considering how fundamentally different the design is versus Chevy's traditional pushrod motors, it makes sense that it would make its debut in the engine bay of an equally radical departure from the norm for the Corvette. Images: General Motors

But a high-revving, naturally aspirated V8 like this speculative LT5 would pair quite well with a potential mid-engined Corvette, and perhaps fit the personality of such a supercar-like layout better than the pushrod V8s GM currently has in their arsenal. It’s also safe to assume its output would be above that of the current LT1’s 460 horsepower.

Of course all of this is far from certain. Chevrolet has offered precisely nothing in terms of official confirmation about the new ZR1, C8, and LT5 – or any other as-yet-unannounced product in the pipeline, for that matter. For now all we can do is make educated guesses. But given the evidence on hand, the hypotheticals detailed above stand a strong chance of coming to fruition.

About the author

Bradley Iger

Lover of noisy cars, noisy music, and noisy bulldogs, Brad can often be found flogging something expensive along the twisting tarmac of the Angeles Forest.
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