Likewise, the Gen III’s output is pretty much spot-on for the 475hp target when the accessories are added to the engine, proving the engineers a quarter-century ago had their slide rules accurately calibrated. The 5.7L LT5 was originally rated at 375 horsepower and upgraded to 405 with the Gen II version of the engine. The original LT5, of course, was a technological marvel of its day. “We were working toward OBD II standards of emissions and engine control,” he says. Ultimate 1957 Corvette Roadster … Yes, Roadster! Lotus patented the technology and sold it a few later, where Porsche and Honda eventually developed variable cam systems based on it. Go see a reputable GM dealership, they’ll get you what you need. As for that variable valve lift system, the idea was to incorporate a finger-follower design with low- and high-rpm lobes, with the high-lift lobes supporting high-rpm performance. For one thing the block was to change to eliminate hydrocarbon-producing fire rings in the bore liners, but there wasn’t a block in the crate, so a Gen II version was substituted. “Overall, that probably cost us about 30 horsepower in the end, but we worked with what we had, using all the prototype parts at our disposal.”. Unfortunately, they also trapped hydrocarbons and promoted detonation. (Image/GM Corporate Newsroom). In fact, Chevrolet reportedly notified Lotus as early as 1991 of their intention discontinue the car, announcing they’d build it through 1995 and call it good after that. The last LT5 production engine was built in November 1993. But because a Gen II block was used for the build, replacement LT5 head gaskets fit the bill. - Day Four Build Recap, Week To Wicked: Two Days Left To Build our 1955 Chevy! All Rights Reserved. This site uses Akismet to reduce spam. There had always been some bruised pride that the engine wasn’t entirely developed in-house or built by the company. The Gen III engine was intended to employ a variable camshaft timing system, with low- and high-lift lobe profiles on a sliding shaft. Click Here to View/Print/Download the Summit Racing LS & LT Engine Reference Guide. Though the dozens of engines in the GM LS and LT families have many similarities, there are significant differences as well—and it’s important to know exactly what those are if you’re upgrading your LS or LT engine for more performance, or planning an LS or LT engine swap. Dailymotion does not manually select the videos appearing on the Topics page, they are generated by an algorithm. It would have been a significant step forward. Work on it had progressed beyond the drawing board to the tooling of prototype parts. Vette. “The ‘squish’ pattern of the original cloverleaf combustion chamber design just wouldn’t cut it for the upcoming emissions standard, but the change nonetheless proved effective at building high-rpm horsepower.”. While these engines were based on the GM Family II engine, the architecture was substantially re-engineered for the new Ecotec application produced since 2000. They also had strengthened blocks, with four-bolt main caps. You can download it in the link below, or keep scrolling down to the tables at the bottom of this story. If you think a video is in an inappropriate Topic, report it to us. There wasn’t even hardware in the parts crate to make that happen, so the conventional Gen I/II camshaft system was installed, including the two-piece Vernier-adjusting camshaft sprockets. That was without any accessories dragging on the engine, a test procedure that duplicated the original SAE 24 tests about 25 years ago. Learn how your comment data is processed. That was done primarily because the new engine controller that would have been used with the engine didn’t support a 16-injector drive system. He was also asked to helm a Gen III version of the engine that would address forthcoming emissions regulations while also pushing output significantly higher. We know of dozens of next-generation vehicles and even variations on existing models that never made it to the production line. The engine was supposed to use an early electronic throttle system, but a traditional cable system had to be used to work with the ’93 ZR-1 project car’s control system. The automotive world is filled with near misses, vehicles and technologies that made it this close to production, only to get the hook just before rolling into the center ring. Graham Behan was a Lotus engineer who oversaw development of the Gen II LT5. Also, the top ring on the Gen III piston was raised to improve emissions performance. Change HR panel circuit and mount, along with the wire harness. “It was disappointing when the end came, because there was so much potential in the basic design,” says Behan. Obvious changes include a revised skirt profile, as well as a flat-top head versus the previous dished top. Corvette Exterior Design Manager shares insights about the C8 Development. The only thing better than winning a brand-new 2019 Corvette is winning a new Corvette and a fully customized 1961 Corvette with $60K included to pay the taxes. According to Behan, the Gen II engine produced 445 horses without accessories during testing, which is about 10 percent more than the 405hp rating in the car. They were headed for the dumpster when that colleague rescued them. The throttle body is an off-the shelf 90mm aftermarket unit. “We had a team of young, eager and dedicated individuals who gave the maximum effort to bring the LT5 to life; and we felt there was more to do with it.”. That helped bump up the compression ratio from the Gen I/Gen II’s 11:1 to 11.4:1. The controller in Lingenfelter’s 1993 ZR-1, in which the prototype engine would be installed, however, did support 16 injectors, so it was directed to treat the eight new injectors as secondary fuel injectors. Search. Want more LS/LT information? Famously developed jointly by Chevrolet and Lotus, and assembled by marine engine manufacturer MerCruiser, the 375-horsepower DOHC engine was universally praised for its high specific output and exceptional refinement. “One of our guys worked out the numbers himself on a piece of paper, using a calculator,” Behan says. They were the “Gen II” versions, which delivered 405 horsepower through head and cam changes. - Day Two Build Recap, Week To Wicked: 1955 Chevy – Day One Build Recap, Win a 1961 and 2019 Corvette with $60-G’s for Taxes, 2019 NSRA 50th Street Rod Nationals…Lots of Corvettes, 1975 Corvette Custom … Blast From the Past, 2020 Corvette Exterior Design Manager Kirk Bennion Interview, A Look At The Three Corvette Assembly Plants. LS and LT Engine Reference Guide for the Gen. 3, Gen. 4 & Gen. 5 LS/LT, Vortec/EcoTec3 Engines, All the Torques: How Summit Pro LS Truck Camshafts Help Truck Owners Maximize Performance. “The parts had been created, but we never got to build the first prototype Gen III engine,” says Behan. That was very satisfying to verify after all these years.”. GM family II 2.0L four valve engine The four valve engine recently introduced in Europe is a further development of the 2.0 litre engine manufactured by HEC at Fishermen's Bend. The heads also use only eight fuel injectors rather than the Gen I/Gen II’s 16-injector design. After spending about 25 years in storage, the parts for the Gen III LT5 were finally assembled at Lingenfelter Performance Engineering, in Indiana, to see if they would live up to the original expectations. Not all of them were in the parts crate delivered to Behan, however, so the Lingenfelter team had to rely on four high-lift cams intended as exhaust camshafts, but still offering strong 0.445-inch lift and 239 degrees duration (at 0.050-inch lift) specs. Week To Wicked: Did We Finish As Planned? I was told you have a kit for it to make it like a 6.3. was checking to see if you could point me in the right direction thanks, Your email address will not be published. “As an engineer and I wanted to see whether the engine would achieve the target power originally conceived for it.”, The C4 ZR-1 set the automotive world alight when it debuted in 1990. Again, the change was designed to reduce emissions, but overall airflow through the new head design increased about 10 percent over the Gen I/Gen II, according to Behan. The engine block for the Gen III LT5 was to be changed from the Gen I and Gen II designs to eliminate their integrated fire rings that helped with cylinder head sealing. Its exotic DOHC LT5 engine was the performance rival of traditional supercars from Italy and Germany. That was about 10 percent greater than a Gen II LT5 head and about 35 percent better than an LS1 head. Sign Up today for our FREE Newsletter and get the latest articles and news delivered right to your inbox. We’ll never know whether the four-door Pontiac Fiero would have made a splash had it gone into production, but the stillborn next-gen HUMMER H3 we saw about a decade ago looked pretty cool. Despite the plethora of parts in the crate, there were still some elements missing that would prevent the prototype engine from being built absolutely as intended.