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LT4 Motor Details

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We just learned a whole lot more about the Z06 LT4 motor thanks to! They interviewed Jordan Lee, Engine Program Manager for GM's small block motors. And the info they learned is exciting, especially his statement that the 625 HP/634 TQ numbers are conservative. As he said,

"We fully expect to beat that number, but we came up with a safe estimate for the show,” boasts Jordan Lee, program manager for GM’s small-block program, also noting that the estimated 634 lb-ft of peak torque should escalate, as well."

Thank you for the following article! said:
The 2015 Corvette Z06 features an all-new LT4 engine. The supercharged, 6.2L V-8 will deliver more than 625 horsepower, and 635 lb-ft of torque. The estimated 625-horsepower figure quoted for Chevy’s new 6.2-liter supercharged LT4 at the Detroit Auto Show unveiling of the upcoming 2015 Corvette Z06 is likely to spiral upwards when the final production model hits the dealerships early next year, according to the engine’s chief engineer.

“We fully expect to beat that number, but we came up with a safe estimate for the show,” boasts Jordan Lee, program manager for GM’s small-block program, also noting that the estimated 634 lb-ft of peak torque should escalate, as well.

The LT4 not only sports a new Eaton supercharger model, but nearly every standard Corvette LT1 engine component was modified, massaged or updated to support the power and packaging goals of the LT4 powertrain team.

The new LT4 engine will power the 2015 Corvette Z06. “The challenge for us was to add 160-plus horsepower but not get any bigger [than the LT1],” Lee tells EngineLabs. “As remarkable as the LT1 is in power density, the LT4 beats it in droves.”

Here’s how the LT4 looks in the Z06 engine bay, zans a few plumbing items.

The LT1, of course, is first of the Gen V small-block engines to hit the market in the new C7 Corvette platform. As EngineLabs demonstrated in previous stories covering the engine’s introduction and an in-depth analysis of the combustion strategy, the LT1 is one of the smallest and most compact engines in the world that is capable of 460 horsepower naturally aspirated. GM wanted to ensure that the engine package didn’t inflate so the Corvette could be offered for sale in Europe. “We ended up about an inch taller only in the back where the supercharger has an airflow path into the intercooler,” says Lee.

Key to the success of adding boost was working with airflow analysis and development engineers at Eaton to improve the supercharger’s efficiency, even though the blower is smaller than what GM utilized on the Gen IV LS9 engine found in the previous C6 Corvette ZR1. That 6.2-liter engine was rated at 638 horsepower at 6,500 rpm with 604 lb-ft peak torque at a stump-pulling 3,800 rpm.

“The LT4 supercharger is 85mm shorter in height than the one on the LS9, and it weighs 20 pounds less,” says Lee. Eaton rates the new R1740 TVS supercharger at 1.7-liter, which means it moves that much air with each revolution of the rotors. The previous LS9 supercharger was rated at 2.3-liter.

“We shrunk the capacity down to 1.74 liter,” says Lee, “but we wanted the same airflow characteristics. So we had to spin the supercharger faster.”

The LT4 will weigh close to the LS9 engine that powered the previous-generation Corvette ZR1. That engine used a larger 2.3-liter Eaton supercharger. The LT4 blower will spin up to 20,000 rpm, compared to the LS9 that maxed out at 15,000 rpm. The smaller rotors also help the supercharger get up to speed quicker, which should boost power earlier in the rpm band. “We worked a lot of the efficiencies through the supercharger to make sure the airflow was up to the quantity levels needed to make the power,” says Lee.

As with the LS9, there is an air-to-water intercooler integrated into the cast-aluminum intake manifold. But unlike the LS9, the new setup features a clamshell core design with turbolator fins inside the water path compared to a traditional tube with aluminum vanes for the core.

The Eaton twin-vortices TVS superchargers are designed with unique 4-lobe, Roots-style positive-displacement style rotors that feature a 160-degree helical twist for improved efficiency with less noise. They will be spinning up to 20,000 rpm on the 1.7-liter version found on the LT4 engine. “It’s a very efficient intercooler,” says Lee. “It’s about 23 percent less volume but has 10 percent improvement in heat-rejection efficiency. It’s probably not thee inches long in length but reduces the temperature of the inlet charge by 150 degrees.”

Adding more air requires additional fuel. The Gen V engines feature direction injection with high-pressure feeds coming from a cam-driven fuel pump.

A cutaway of the new LT4 was on display at the Detroit Auto Show where the Z06 announcement was made. It’s shown next to a mockup of the 5.5-liter Gen V engine that powers the next C7.R race Corvette. “The biggest challenge was the fuel pump itself,” explains Lee, noting that other exotic DOHC powerplants have up to four pumps to serve the fuel system. “With only one pump we had to increase the size and displacement to handle 625-plus horsepower worth of fuel.”

GM increased the piston size in the pump but didn’t have to change the tri-lobe cam design that drives the pump. Fuel pressure in the lines was increased — the LT1 fuel system operates at nearly 2,200 psi, but no figures were given for the LT4 — and the cylinder heads received larger injectors. The LT1 cylinder ports didn’t need any additional breathing room, but a lighter titanium intake valve was preferred, and the LT1 cast piston was swapped for a forged version that offers a lower 10:1 compression ratio (the LT1 was 11.5:1).

“The 10:1 is till relatively high for a boosted engine,” says Lee, adding that max boost levels will be around 9.5 psi. “We also optimized the camshaft to get the torque and power curves we wanted. The lobe centerline spacing and lift profile are a little different from the LT1.”

The LS9 was also equipped with titanium intake valves as well as titanium connecting rods. “We didn’t need titanium connecting rods to get the balance we required on the LT4,” counters Lee.

The LT4 features dry-sump oiling, and the oil cooler has been enlarged over the standard Z51 option setup. In addition to the forged pistons, GM did beef up the entire rotating assembly. The crank is forged with a higher strength steel alloy than the LT1, and the connecting rods are fully machined.

“We added a lot of extra machining on the flanks for light weight,” says Lee. “Also, we annodized the lands on the piston and went with a PVD-coated ring. Finally, the piston pin has DLC coating to handle the extra temperature and pressure.”

Additional durability measures include constructing the cylinder heads with Rotocast A356T6 aluminum and casting the exhaust manifolds out of stainless steel. Overall, the engine weight will come close to the LS9. “The 20-pound decrease in the weight from the supercharger offsets the weight from the additional technologies like the DI pump, the cam phaser and AFM. We’ll end up with an estimate round 240 kilograms (529 pounds), which is where the LS9 came in.”

Finally, GM officials refused to speculate on the future availability of an LT4 crate engine when reminded that the LS9 eventually became part of the Chevy Performance catalog. But Lee does offer a reassuring hint: “We pride ourselves on making the small-block available to the aftermarket.”
For entire article with more engine pictures:

LT4 Engine?s Chief Engineer Hints More Power Is Coming - EngineLabs
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If you haven't previously seen tons of details about the Z06's LT4 motor, enjoy your reading in this thread. Note, that the thread's original post was five months ago, before the LT4's 650/650 SAE certification numbers were revealed.
As I read deeper into this article, my smile grew larger and larger as it addressed various issues required to seriously take into consideration when adding forced induction to engines. The methods used in resolving various issues in the heart of the engine (Bottom-end) were addressed. The cam timing (profile) was also addressed as well. There are huge differences between how engines are built between being naturally aspirated and supercharged and turbo charged.

What kills me is a number of enthusiasts out there will buy a new car with with a naturally aspirated engine with total disregard for the factory warranty and slap a $6,000.00 aftermarket supercharger on it and think they're good to go.... If you notice, the LT4 has a set of 10.0:1 "Forged" pistons, for a lower static CR than the 11.5:1 cast pistons found in the LT1. They admitted the 10.0:1 CR in the LT4 was "Still relatively high for a boosted engine." Many aftermarket supercharger manufacturer's often recommend dropping the static CR down to 9.0 to 9.5:1 in order to run around 8-9 lbs. of boost. The problem is, if your already running 10.5+ to 1 or in the LT1's case 11.5:1, even 4-5 lbs of boost can create catastrophic engine failure, unless of course your running E85 or special $12-$15 a gallon race fuel or methanol, which is highly corrosive.

This new LT4 is obviously a very well thought out engine design and should serve it's owners quite well over an extended period of time 5-years/100,000 miles. :) The technology displayed in both this new supercharger and inter-cooler I found quite interesting. It's really come a longs ways over the years. I'm really looking forward to adding this new LT4 in the new Z06 to my stable of cars next year.
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