Here’s Why Chevrolet Ditched the Pushrod Engine for Its 2023 Corvette C8 Z06
Everyone is aware of the Corvette’s contribution to the automotive scene. For those unaware, the Corvette’s heritage spans eight generations, the most recent being the very first mid-engine design. The Chevrolet Corvette 2022 C8 has had quite a reception since its launch not too long ago. Its impressive performance at a relatively accessible price allowed the Corvette C8 to quickly gain popularity, with demand outstripping supply even today.
Corvette’s moniker made quite an impact when General Engines launched it in 1963. With its timeless curves, the Chevrolet Corvette managed to instill a sense of desire in the mind of every American, regardless of age. A similar buzz, one reminiscent of 1963, was felt when GM officially unveiled the mighty C8 Z06.
However, this is not the usual Z06 exercise that we know. What the C8 Z06 has that none of its predecessors could ever dream of is a bespoke flat gem of a V8. Yes, the 2023 Z06 ditches the pushrod design in favor of a bespoke high-revving LT6 V8. But what drove Chevrolet to such a decision? Let’s find out.
GM’s New LT6 Double Overhead Cam Replaces LT4 Pushrod V8
The new 2023 C8 Z06 uses a hand-built, 5.5-liter flat-crank, naturally-aspirated V8 dubbed the LT6. The engine is totally matched to the 2023 Z06, and you won’t find it in any other Chevy or GM product. Power figures come in at 670 horsepower with 460 lb-ft of torque. A whole lot of engineering magic went into this new howler of a V8. We will cover the details in the following sections. Oh, and the LT6 engine in the 2023 C8 Z06 also happens to be the most powerful naturally aspirated production V8 there is.
The C7 Corvette Z06 featured a new supercharged 6.2-liter V8, dubbed the LT4 powertrain. Output was 650 horsepower and 650 lb-ft of torque. Several improvements were made to the engine, which was basically a small block LS V8, despite being a newer generation. The 6.2 featured direct injection, variable valve timing and an active fuel management system to improve performance and efficiency. While the LT4 and LT6 are no slouch, they behave in two very different ways. One is about max attack, while the other has a sense of duality in mind.
What was the driving force behind the discontinuation of the Pushrod V8?
The answer is less rotational inertia, better response and better traceability. If you know your engines, you’ll be familiar with pushrod engines and their inability to sustain high RPMs. In a V8 tappet, the valves are actuated through rocker arms connected to a tappet that receives inputs from a single camshaft. Between the valves and the camshaft are many components that are arranged in such a way that high engine speeds could overload their complex movements and cause the valves to float. To be more specific, the push rod has a reciprocating motion, which has relatively more resistance or inertia than the circular motion. To eliminate inertial forces and make way for a meatier top end, GM engineers decided to go the DOHC route, abandoning the pushrod design.
Let’s take a closer look at the LT4 and LT6 architecture
The LT4 was designed specifically to handle the additional stresses induced by forced induction. The higher output meant the internal components had to be strong to work for longer periods of time. Most notable was the adoption of Rotocast T6 aluminum cylinder heads which are much stronger and better heat-dissipating than conventional aluminum cylinder heads. Having forged connecting rods allowed for increased tensile strength and reduced reciprocating inertia, which allowed for efficient power delivery.
Using lightweight titanium valves meant reducing unwanted reciprocating mass and reducing valve float at high rpm. Although it has not been eliminated entirely, due to the design of the push rod. The introduction of direct fuel injection meant that the LT4 could run a higher compression ratio of 10:1, relatively high for a forced induction engine. On top of that, the LT4’s forged aluminum pistons meant better material strength and less inertial forces during piston movement.
As for the LT6, the signature of the engine is a crankshaft with four jets located in a single plane. The layout is commonly referred to as “flat” – compared to the usual 90 degrees of a traditional “cross-plane” V8. Key to the LT6’s performance capability is a lightweight, low inertia rotary assembly with a short stroke design, allowing for an 8,600 rpm redline. What you’ll find inside are forged aluminum pistons and forged titanium connecting rods for low mass and high strength. Titanium intake valves and sodium filled exhaust valves are available with dual coil valve springs for sustained performance. The engine runs at 12.5:1 compression, allowing the LT6 to deliver excellent volumetric efficiency. Also worth mentioning is the LT6’s all-new active split intake manifold. This allows the Z06 to consume more than one air pressure despite its naturally aspirated design.