It’s not uncommon to release truly new and truly exciting high-performance engines for production cars, so when things like the C8 Corvette Z06’s LT6 go down, it’s worth taking a closer look. The 5.5-liter flat crank V8 adds luster to the engine compartment of the Corvette, which is most focused on the track, producing 670 horsepower without the help of any forced induction. We have done a lot of reading and research to find out how, but we also talked to Josh Holder, chief engineer of Corvette, who explained the ins and outs of this mechanical masterpiece.
First, it is worth providing some background information. This new naturally aspirated V8 has more horsepower than the previous Z06 supercharged block, which has a larger displacement of 6.2 liters. how? Everything is related to air flow, which is determined by the engine's cylinder head and all the components connected to it. The blown LT4 used in the old Z06 is a classic push rod design with a cross-plane crankshaft. The flow rate in the push rod design is limited by the number of head valves (basically two in modern gasoline applications) and the path the push rod itself extends into the intake and exhaust ports. Since the beginning of the 21st century, putter head design has come a long way-you can do all kinds of tricks to get the putter away from the port-but the dual overhead cam layout will always be able to circulate more air.
This is why the LT6 adopts the DOHC layout. In this regard, and many others, it follows the lead of the C8.R racing engine. According to Holder, this road car power plant shares a lot of parts with the parts you find in Le Mans competitors. "Except for a few hardware, the cylinder head is basically universal," he said in a conversation with The Drive. "Turn your head upside down...the combustion chamber, the valves and the ports, they are all CNC machined. They look like they just got off the car."
The specifications of the head itself are impressive. The flow number of the port is not provided, and the port volume is not provided; however, the valve itself is very large due to the 4.104 inch orifice. For reference, the largest mass-produced small-displacement Chevrolet 7.0-liter LS7 has a bore of 4.125 inches. The 58.8cc combustion chamber in the head also allows a compression ratio of 12.5:1-high-quality fuel is needed here.
The diameter of the intake valve is 1.654 inches (42 mm), and the diameter of the exhaust valve is 1.378 inches (35 mm). The valve lift figures cannot be confirmed, although they must be high considering that the engine produces peak power at 8,400 rpm and peak torque at 6,300 rpm. For reference, the high-revving 3.2-liter inline six-cylinder S54 of the E46 BMW M3 produces peak torque at 5,000 rpm and peak power at 7,900 rpm. Due to the higher peak torque rpm, this LT6 may be hotter than the LT6, and its volumetric efficiency is also higher; 121.8 horsepower per liter, while the M3 is 104.1.
The LT6 does not have a variable valve lift system, but its hollow camshaft is equipped with variable valve timing. According to Holder, the cams are phased by an electro-hydraulic system that allows approximately 55 degrees of authority on the intake cam and approximately 25 degrees of authority on the exhaust cam. This cam phasing capability should help the engine to be easier to drive in the low speed range.
The cam itself presses on the finger follower, which in turn acts on the titanium alloy intake valve and sodium-charged exhaust valve. The valve is controlled by a double valve spring at a high speed, and the smaller spring is located on the larger exterior. The LT6 has a solid tappet-the tappet is the part between the cam follower and the valve itself-which usually needs to be adjusted over time. However, Chevrolet says you don't need to adjust the lifter on the LT6. This is because it creates an automated tool that ensures a very precise fit between the finger follower and the lift itself. Most importantly, the car manufacturer has installed a fuel injector that flows through the finger follower and sprays directly on the area where the cam surface meets the finger follower. Chevrolet says this will help maintain extremely consistent tolerances throughout the life of the engine. Only time will tell if adjustments are really needed, but Chevrolet may have tested very similar settings in C8.R and seems confident.
"The engine is handmade in Bowling Green as part of the [precise lifter fit] process... The cylinder head and cam cover are fully assembled, the running clearance is measured, disassembled, and the running clearance measurement enters the calculation robot pre-selected The gasket is put back into the finger follower for a net fit.” Holder said, detailing the matter. "So we excluded all the structural changes, reassembled the head and measured it again to make sure it was good and passed that station. Then when the head was bolted to the engine, we measured it again."
There is no need to delve into the dry sump lubrication system, I know that many people will definitely want to listen to it, which is very interesting. LT6 uses 5W50, which pumps through the engine very efficiently. There are four points in the crankcase and two points on the head where the oil is swept back to its remote oil pan. The automaker said in an interview with Road & Track that in most cases, as much as 80% of the oil remains in the oil pan. The oil is pumped into the engine to complete the lubrication work, and then quickly returned to the oil pan. If you want more power, you can't let oil get in the way, and the LT6's lubrication system prevents oil from entering the path of fast moving parts such as the crankshaft.
Each crank pin also has its own crankcase compartment, which can more effectively remove oil spilled from the crank pin (the journal connected to the forged aluminum piston) by reducing wind resistance. These areas are where the cleaning points are located. There is also its own fuel injector under each piston to help cool the combustion chamber.
An important part of keeping the oil system working is of course filtering, and the LT6 has a bolted cartridge filter. This is not because the engineering team just likes this approach, but because of the vibrations associated with the flat crank. "When we first built our earliest engine on a dynamometer, we saw the engine immediately spin the cartridge filter [due to vibration]," Holder said. "We now have this cartridge filter. [It] does not rotate. It is bolted."
This nasty vibration was an obstacle for the team, and was different from the problems faced by the 5.2-liter Voodoo V8 of the Ford Mustang Shelby GT350. The large flat V8 engine shook like crazy. Chevrolet not only solved this problem, but also used an oil filter that would not fall off on its own. It also used other smart features, such as the most important fluid damping installed on the crank. Device. There is no balance shaft or anything here, be clear. The damper works with a series of lighter rotating components in an attempt to reduce resonance. Smaller components such as electrical connectors must also be reconfigured to ensure that they do not fall off on their own throughout the life of the engine. Holder said that all these features have been proven on the track.
The crankshaft itself is forged steel, and each main cover is bolted to the cylinder block with four bolts. It defines the 3.150-inch (80 mm) stroke of the engine, which is quite short compared to the 4.104-inch bore of the engine mentioned above. This is a typical feature of a high-revving engine. In fact, the LT6 has one of the shortest bore/stroke ratios in any production power unit. Fortunately, Engineering Explained did this research and listed the bore/stroke ratios of some other cars for comparison, so we don’t have to do this. The bore/stroke ratio of the LT6 is 1.3:1; compare it with the current Porsche 911 GT3's 1.25:1, the Ferrari 458's 1.16:1, and the regular C8's 1.12:1. As an extreme reference, the F1 car has a bore/stroke ratio of 1.51:1. The higher the ratio, the higher the theoretical "recoverability". Forged titanium connecting rods make this recoverability sustainable. The entire bottom end of the LT6 is also forged, including the piston and crank.
Other intake and exhaust techniques, such as three throttles between the two main intake boost chambers, also help to improve torque, power and driving performance. These valves affect intake resonance and intake boost volume. They are programmed to open and close throughout the rpm range in order to keep the maximum torque for longer. How this actually makes the engine produce more or less output is a rabbit hole, but it is briefly explained in the embedded E/E video.
The exhaust system's tricks include the inverted horn shape, which is detailed in the car's display, and helps to increase the exhaust noise in the cabin. The exhaust system itself is a 4-2-1 setup, four exhaust pipes are merged into two, and then these pipes are merged into one. This setting is used in conjunction with the plane layout of the engine to achieve excellent exhaust purification, which is essential at high speeds. If you are not sure how it works, exhaust purge is a process through which exhaust pulses traveling along the exhaust pipe help attract other pulses under the pipe. When you have a high-revving engine, increasing exhaust flow is essential. Effective exhaust scavenging can increase exhaust flow.
All these features add up to an incredible output of the LT6. Even more fascinating is that the price of a car with this engine may be less than $100,000, and it shares real parts with the C8.R race car. "This is not just a marketing slogan. This is a fact," Holder told us. "[We] actually share parts with the racing team. We may be missing parts to update some of our development vehicles, and we will call them. They will bring them over, and vice versa. We will go to meetings together."
This joint development makes the most powerful naturally aspirated V8 ever installed in a production car relatively cheap. Impressive engines such as supercars that are expected to be worth millions of dollars, but only a few people will like them. Fans rarely dream of having something so special without having to plan to become a millionaire. Speaking of ordinary hobbyists, Holder believes that there are still many people who want a machine like the one he helped create.
"[LT6 is] the pinnacle of years, like standing on the shoulders of giants," he told us. "It's built into this engine. It's a way of celebration. It's not just an internal combustion engine, but the pure pleasure of driving the sound it makes. It makes you feel connected to the machine."
"There are still many people who desire this experience," he concluded.
Are there any hints or questions for the author? You can contact them here: peter@thedrive.com
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