5 ways the 2020 Corvette’s midengine layout led to a better Chevy small-block V8

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November 12, 2019 01:00 PM

5 ways the 2020 Corvette’s midengine layout led to a better Chevy small-block V8

It might still be a naturally aspirated 6.2-liter V8, but the C8’s LT2 packs plenty of new tricks.

Graham Kozak

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The 2020 Chevrolet Corvette’s LT2 V8 may be superficially similar to the LT1, but there’s a lot new going on inside.

As different as the 2020 Chevrolet Corvette is from its predecessors, there is one key point of continuity: It’s still powered by a naturally aspirated 6.2-liter V8, a direct descendent of the famed small-block engines General Motors has been bolting together for 64 years. And those engines will be assembled at the Tonawanda, New York, factory that built the first GM small blocks back in 1955.
But if the new ’Vette’s V8, dubbed the LT2, has a lot in common with the C7’s LT1, it’s also evolved substantially to better fit its new midengine role. In some cases, the new format enabled Chevy’s small-block engineers to push the engine’s performance envelope; in others, it demanded that they tackle old problems in a totally new way. The result is an impressive implementation of the classic small-block formula with a set of supercar-like performance specs to back it all up.
We recently visited GM’s Pontiac, Michigan, Performance and Racing Center to learn exactly what’s going on under the LT2’s “Venthan red” valve covers—and how the challenges presented by the midengine approach ultimately led to the new Corvette’s 495-hp, 470 lb-ft heart.

Steve Fecht courtesy of Chevrolet

A cutaway of the LT2’s composite oil reservoir, mounted to the front of the engine.

1. It’s all dry sump, all the time
If you ordered anything other than a base model C7 Corvette, including the Z51 performance package, you were getting a car equipped with a dry sump lubrication system. On the 2020 Corvette, all cars are dry sump, meaning much of its oil is stored in a reservoir tank mounted to the front of the engine rather than sloshing around in the crankcase.
The LT2’s oil pan is roughly 1 inch shorter than the pan on dry sump-equipped LT1 engines, reducing mass (by about 5.7 pounds) and helping drop the entire engine assembly lower to the ground. The oil volume has been decreased to 7.5 quarts, a 2.25-quart reduction over dry sump LT1s.
At 6,000 rpm, Chevy says only 1 quart of that oil is in the engine; the rest is elsewhere in the dry sump system—namely, the composite tank (which includes an integrated oil centrifuge, oil separator system and internal baffles) mounted to the front of the engine.  
The big advantage of a dry sump system, especially on a performance car like the Corvette, is that it helps avoid engine oil starvation while whipping a car around, for example, a track. In this case, Chevrolet claims the LT2 can handle 1.25 g sustained lateral accelerations in any direction.
And, of course, there’s the weight savings of a little over 2 fewer quarts of oil in the system.

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A look at the Chevrolet LT2’s lubrication system. The upper portion of the engine is serviced by the valley scavenge pump; it’s sealed off from the crankcase.

2. Three oil pumps, two chambers
Changes to the LT2’s lubrication system don’t stop with the dry sump setup. You can think of this engine as being divided into two chambers: the block valley up high, and the crankcase down low.
On a more conventional engine, gravity would pull oil from the upper chamber into the crankcase. This is simple and more or less bulletproof; trouble is, the oil passes over lots of spinning bits—namely the crankshaft—on the way down, agitating it and introducing undesirable air into the lubricant mix.
On the LT2, the block valley is sealed; it’s effectively a separate oil chamber. Instead of relying on gravity, the flow of lubricant is regulated by a fixed-displacement chain-driven scavenge pump, which sends oil back into that engine-mounted reservoir. The lubricant flow through the lower chamber is regulated by two crank-mounted pumps: one variable displacement supply pump and one two-stage scavenge pump.

Chevrolet

The Chevrolet LT1’s intake plenum has a volume of 11.1 liters, while the LT2’s has grown to 14.1 liters. But you don’t need the numbers to see the difference.

3. It inhales more freely …
If you want an internal combustion engine to make more power, it’s going to need (among other things) more air. On a naturally aspirated car, that’s going to mean a bigger air intake. But you can only go so big before you’ve got to bust out the sawzall and cut a hole in the hood … unless you stick the engine behind the driver.
Because the engine sits lower in the 2020 Corvette, and its midengine placement eliminates concerns about hood height—and subsequent impact on forward visibility—engineers were able to increase the LT2’s intake manifold to 14.1 liters, compared with 11.1 liters on the LT1. You don’t even need the numbers to know there’s been a change: A quick glance at the LT2’s tall, arched plenum makes the LT1’s look like a squashed pancake in comparison.
Further, engineers were able to give all LT2 intake runners an equal, 210 mm length, which helps ensure consistent, even airflow to all cylinders. The LT1 used 225 mm runners, except for cylinders two and seven, which were shortened to 185 mm to accommodate the fuel pump. The throttle body is, at 87 mm, the same size on both new and old, though the LT2’s now faces rearward.
Overall, Chevrolet claims that the LT2’s intake setup alone accounts for a 3 percent increase in power, compared to running an LT2 engine with the older LT1 intake.

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The Chevrolet LT2’s exhaust system is far more compact than the LT1’s, a function of the 2020 Corvette’s rear-midengine layout. Also note the single catalytic converter, versus the pair of cats used on the C7 Corvette.

4. … and exhales more freely
It’s a shame that so much of the LT2’s exhaust system is hidden; it’s an almost-sculptural piece that wouldn’t look out of place on an exotic car costing far more than the (barely) sub-$60,000 Corvette. Peering beneath the engine cover, you might be able to catch a glimpse of the upswept four-into-one exhaust manifolds—now fabricated, rather than cast—but the rest of it is tucked away behind the transmission.  
The switch to a midengine layout mandated a radically different exhaust system setup, but engineers were able to eke out performance advantages here, as well. Compared to an LT2 engine equipped with an LT1 exhaust manifold, an LT2 engine with the new LT2 manifold posts a 1 percent power increase—not as dramatic a difference as the intake, but a bump nonetheless. There’s a weight advantage, too; the switch to fabricated manifolds amounts to a savings of 200 grams, or 0.44 pound, per side.
And the setup offers benefits that go beyond pure performance. While packaging constraints on the C7 Corvette meant that catalytic converter duty was split between two units, one after the exhaust manifold and another farther downstream underneath the car’s floor, the LT2 gets by with a single converter just aft of the manifold. It’s an all-around cleaner assembly, and positioning the converter closer to the engine—where the exhaust is hotter—has advantages for emissions management, as well.

Chevrolet

The Corvette’s LT2 mated to its eight-speed dual-clutch transmission.

5. It’s all tied together
One thing Chevy’s engineers emphasized at seemingly every turn is how nearly all improvements that made their way on to the LT2 were facilitated, and in some cases mandated, by the Corvette’s switch to a rear-midengine format.
Or, as Jordan Lee, chief engineer of small-block engines, says of all of the tweaks large and small, “We’re not stupid because we didn’t do this on the LT1.” Engine development and platform development—it’s all tied together in a sort of guided evolution from the LT1.
The less restrictive intake and exhaust flow, for example, allowed the engineering team to start playing with the valvetrain and camshaft; consequently, the exhaust valve lift has been increased by 1 mm to 14 mm, now matching the intake valve lift. Both intake and exhaust valve duration have been increased.
And the new dual-clutch transmission, a compact, complex engineering marvel unto itself, has an input axis (connecting the engine to the transmission) that actually sits below the output axis (connecting the transmission to the wheels via half-shafts). Because of this, the engine could be placed down low in the chassis for better weight distribution—something also enabled by that thinner oil pan.
As for what’s next for the new midengine Corvette, Chevy won’t reveal too much. Forced induction feels inevitable; an exotic flat-plane crank V8 is possible, as is an even more exotic hybrid system.
For now, though, there’s only the LT2, all 495 hp and 470 lb-ft of it. Familiar yet new, it’s a full-throated link to the Corvettes that preceded it—and an indicator of just how far large-displacement, American-made performance can still take us.

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Source:https://autoweek.com/article/technology/5-ways-2020-corvettes-midengine-layout-led-better-chevy-small-block-v8

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