Chevy’s recent reveal of the all-new flat-plane crank 5.5L V8 LT6 engine in the 2023 Corvette Z06 probably got many of us thinking about Corvette engines of the past. Today, let’s take a look at the Lotus-developed 5.7L V8 LT5 that powered the C4 Corvette ZR-1 (not to be confused with the supercharged LT5 in the C7 Corvette ZR1).
Yeah, we hear you. Regarding the LT5, it’s confusing to have the same engine code applied to two different powerplants, but at least they both powered ZR1 Corvettes.
Yet, the Lotus-designed LT5 actually has some general similarities to the new flat-plane crank LT6. The LT5 in the C4 Corvette ZR1 was a naturally aspirated, all-aluminum, 32-valve, DOHC small block V8, much like the LT6 in the 2023 Corvette C8 Z06. But it didn’t have a flat-plane crank, and is not a Chevy Small Block V8 even though both engines share the Small Block’s signature 4.4-inch bore spacing.
For the 1990 model year, Chevy launched the “King of the Hill” C4 Corvette ZR-1 with the LT5. Output of the LT5 was impressive at that time, producing 375 horsepower and 370 pound-feet of torque. Lotus designed a unique air management system to provide a wider power band by shutting off eight of the 16 intake runners and fuel injectors when the engine was at part-throttle, while still giving the C4 Corvette ZR1 those 375 horses when at wide open throttle.
In 1993, GM increased LT5 output by 30 horses and 15 pound-feet of torque (to 405 and 385, respectively) thanks to four-bolt main caps, improved cylinder heads, new pistons, revised cam timing, and new exhaust manifolds. Many of those innovations are common now, but they were revolutionary in the 1990s.
Perhaps the most exotic and radical engine to sit in a Corvette until the LT6 in the C8 Z06, the LT5 in the C4 Corvette ZR-1 was engineered by GM and Lotus, then machined and assembled by Mercury Marine’s MerCruiser division in Stillwater, Oklahoma. The GM-Lotus tie-up came about in 1986, when General Motors had acquired Group Lotus, a UK-based engineering consultant and performance car manufacturing firm. The Corvette team wanted to build the world’s fastest production car based on the C4 Corvette and approached Lotus with the idea. Hence, the LT5 was born, replacing the L98, which had the same bore centers.
In addition to the LT5 engine, Lotus helped GM design the upgraded braking and steering system in the C4 Corvette ZR-1. The range-topping Vette was also shod with custom-made Goodyear Eagle Gatorback tires, sized P315/35ZR-17. Due to the heavier engine and body along with wider tires, the C4 Corvette ZR1 was 200 pounds heavier than the standard C4 Corvette.
To manage the increased weight, the FX3 suspension system was engineered by Bilstein and was similar to the system used in the Porsche 959, but with modifications from the Lotus Formula 1 division. It incorporated a gas-over-oil shock absorber with a hollow center shaft that was fitted with an adjustable orifice to controls the flow of oil. The setup allowed for six damping settings in each of the three driving modes, namely Touring, Sport, and Performance, and had 14 total steps. Servomotors coupled with a microprocessor governed the vehicle’s speed and adjusted the suspension system accordingly.
Thanks to the engineering marvel that was the LT5, the C4 Corvette ZR-1 was incredibly quick for its time, hitting 0-60 mph in just 4.4 seconds and the quarter-mile in just 12.7 seconds, on to a top speed of over 180 mph. It was so quick that it set seven international and world records at a test track in Fort Stockton, Texas, on March 1st, 1990.
Ready to see it in action?
Check out a retro review from MotorWeek taking the 1990 Corvette ZR1 through its paces in Europe, and then watch then-Corvette development manager John Heinricy and four-time Indy 500 winner Rick Mears bang through the gears of 1992 Corvette ZR1.
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Comments
The true story of the ZR1 is seldom told.
The car generated a lot of press and excitement but was not that great of a leap over the standard engine. In fact GM held up the next gen engine as it held more power and was much cheaper to build and buy.
GM also was short lived with Lotus engineering as few companies would work with the under GM ownership. GM had hopes they could contract out like Porsche engineering.
It was an exciting plan, car and time that just did not work out as planned.
GM at least did not give up on the idea of a super vette.
Today the original ZR1 is getting talked about more I believe in hopes it will stimulate values as they have been stagnate over the years. The limited numbers should help but the demand just never took off. My boss has one as they have been easy to buy but at time some parts can be very difficult or expensive to buy.
I always liked how the rear of the car was wider with bigger tires. The Vette team did not take the easy way out.
Another factor here was the decline in C4 sales put the car on the hot seat. It was bad enough GM ordered work stopped on the C5 stopped. A couple of people at Chevy hid the program and finished it luckily.
Most two seat cars live short lives. The Corvette is a survivor that is rare in many vehicle but in two seat cars 10 years or less is too common for many models.
The ZR-1 was a slow program that could have/would have done better if it was on the market 2-3 years sooner. These cars are strongest at higher RPM and were built and tuned for top speed, not drag racing. The L98 of this era has strong low end torque, but just as they “run out of breath” , that is where the DOHC LT5 comes alive and pulls and pulls. The new LT6 engine will in some ways be the same, it makes max power at well north of 8000 RPM.
The value of these cars is on the rise, you need to go have a look at recent sales on BaT.
Well if you compare today’s new DOHC to this you will find that this engine while advanced for its time was still lacking some key elements.
Today the variable timing is enhanced with higher compression that was set free by the Direct Injection and oil cooling.
Like many of the advanced things GM tries often they bring it to market before the real tech to make it work right is available.
The saddest thing was watching them line them up at the factory and crush them with a JCB digger. As the modified test cars could not be sold the public 🙁
I came across this engine in the engineering garage at Rochester Products Div. sometime in 1985. It totally blew my mind that GM had built this engine with 2 injectors per cylinder, an exotic intake, and what appeared to be overhead cams. Keep in mind, performance was barely creeping forward and had been almost non-existent for many years. Today we’re seeing the the benefits in GM’s product line when engineers and top design teams drive product development. This LT5 engine was a major milestone and bedrock for Chevrolet Performance.
Lotus is king so glad they are staying in the news now. Can’t wait for the evija.
I just love these cars and the looks of the C4 Corvettes.
Had a chance to purchase this engine off BAT a year or two ago. I intended to drop it in my normal C4 that is also an automatic. Clearly this conversion would have been a lot of work, but possible. After hemming and hawing to make a decision, I finally decide to pull the trigger and did not realize the auction had ended 2 hours earlier. Ughh. The engine was local to me also. That time of indecision hurt.
There is a guy in New Zealand that runs one, very fast. Back in the day you needed a VIN# to even buy a zr1 badge. The ol’ wine glass on a running engine was one of its parlour tricks.
@C8.R nice try there 🤡
True story of the ZR-1 :
This car came during a lengthened C4 generation that should have been in a c5 come 1993. With a recession and the fact that this was pre social media had a huge impact on its popularity. All the sports cars of the 90s suffered from the same fate. Low sales, recession, high interest rates, and pre fast n furious aftermarket boom and social media era boom. That’s why they all disappeared. C4s weren’t raced hard back then their image was more of a retirement car. They were hardly ever seen at the drag strip and as you all can see now how popular they have been after the c5 at the road courses and drag strips. In the 90s that was left to the fbody Camaro /firebirds/ta.
The engine itself is a marvel and is still a marvel even today. C8.R compared this to the small block but the L98 is a pathetic excuse for a small block designed for pickup trucks with garbage bottom tier parts all over it. The new c8 zo6 will have excellent power. This LT5 can be built even today to far exceed that power without direct injection. Without variable valve timing. Without dry sump oiling among other things. Add to that this LT5 is beautiful and sounds absolutely incredible as well.
I absolutely love mine. In the planning stages for a 700+ Hp 427ci stroker build for it. Long love the King 👑
Um these cars were raced, in fact they were so good on the track they got banned from showroom stock racing and had to start there own series corvette challenge
Well, apparently C8r has never been in a zr1. There is absolutely no way the l98 would ever come close to lt5 performance.. I don’t care what you do to it. The heads flow 188cfm 🤣 I own a 92 Zr1 and after 5,200 it comes on Very hard.. 28degrees of timing hard all the way to 7,200rpm.. And there is a reason it’s 24hrs at 175mph world record still hasn’t been beaten.. And the other record of 5,000 miles at an average of 175mph with fuel and drivers change stops.. Still standing.. this car holds more land speed record than any production car.. 30 years ago. I’d love to see any 2 valve LS based car attempt that same feat. Don’t get me wrong, I love LS stuff. Had a 1,000rw c6 for a long time. But there is no 2 valve V8 that gm builds that will make the power the lt5 does above 7,000rpm. I’ve owned 8 corvettes, and none have the charisma of the lt5.. put your foot in it and it has deep big block pull and induction sound.. and it pulls like that to 7,200rpm.. I also have an 02 Lotus Esprit V8 with gt28s that makes 550rw. The ZR1 feels a lot more like the 918 in the Esprit more than any other V8 gm has ever had. When the c4 ZR1 came out, my dad pulled out a hemmings motor news to show me the 70-72 ZR1. One was for sale for 25k then… I think they sell for 400k now.. and now you know why I have a ZR1 in the stable 😉 Go drive one. You will think so differently after the yacht spins past 5k.. If you don’t watch the tach, you’ll hit the limiter everytime. They never fall over..
Hi Jason,
Great narrative… love the 918 association. I’m a C4- ZR owner… vintage ’91. I bought it in LATE ’91, and just did a minor resto… Still a beast, and there’s nothing around that beats the sound of the LT5. My Bias understood… I think the C4-91ZR might have a place in all ZR-1 enthusiasts hearts. Performance wise, it was the first “super-car” for domestic OEM’s, and the LT-5.0 officially opened the door and paved the R&D road to the C-8. I think we all hope they continue the investment.
Hi everyone. My dad, Haywards Brooks was part of the LT5 design team that came over from Lotus in the late 80s to the Mercury plant in Stillwater. I was 5 years old at the time and still remember the year we lived in Oklahoma. Quite a change from Norfolk in the UK haha. My dad passed away about 15 years ago but I’m slowly starting to piece together his achievements and he always remembered this as one of his proudest. It’s great to hear so many of you still loving the Zr1! I actually have a photo framed and signed by the whole engineering team of the LT5 that was given to my dad on the day we flew back to the UK. It’s one of my treasured possessions. In April I’m planning a road trip as I’ll be in Austin and I’m heading to see the old mercury marine (now ASCO I believe) plant where he worked. It’ll be like a pilgrimage for me and of course, I’ll be making the 900 mile round trip in a Corvette. 😉