The Gen-V small-block's cylinder head design builds on the excellent, racing-proven airflow attributes of previous small-block heads
and matches it with a direct-injection combustion system. It supports tremendous airflow at higher rpm for a broad horsepower band,
along with strong, low-rpm torque.
Compared to other Gen-V variants, the LT4 uses aluminum cylinder heads produced with a rotocast manufacturing process, which rotates the
head mold as the molten alloy cools and essentially eliminates porosity, or microscopic pockets of air trapped in the casting. Rotocasting
delivers a stronger part that helps maintain performance and structural integrity over the life of the engine.
The heads are cast in a premium A356T6 alloy, which better manages the heat generated in a supercharged engine.
A356T6 also pays dividends in the thinner bridge area between the intake and exhaust valves, where effective heat dissipation is
crucial to both performance and long-term durability.
Compared to the naturally aspirated LT1 head, which features 59.02cc combustion chambers, the LT4 has a slightly larger 65.47cc chamber
size designed to complement the volume of the piston’s dish. The chamber size and piston dish work together to produce a 10:1 compression
ratio – a full 1.5 points lower than the LT1's 11.5:1 compression. Lower compression than a comparable naturally aspirated engine is required
of a supercharged application to stave off knock or detonation that can occur as a result of the forced-induction engine’s higher cylinder
As with other Gen-V variants, the LT4 head features large, straight and rectangular intake ports that feature a slight twist to enhance
mixture motion. This is complemented by a reversal of the intake and exhaust valve positions as compared to the Gen-IV design.
The exhaust port shapes are optimized for the new valve locations, with new port opening locations at the manifold face.
Large, lightweight valves are used in the LT4's heads, including 2.13-inch (54mm) titanium intake and 1.59-inch (40.4mm) hollow sodium exhaust
valves. The exhaust valves are manufactured from a high-chromium steel alloy called 21-43 (SilChrome 1 is used at the tip only, the valve
is made from 21-43). At normal operating temperatures, the sodium inside the valve stem melts and becomes liquid. The liquid sodium improves
conductivity, promoting heat transfer away from the valve face to the cooler end of the stem, where it more readily dissipates through the
valve guide. This maintains a lower, more uniform valve temperature, reducing wear on the valve seat for a consistent seal between the valve
and head over the life of the engine.
The valves are held at 12.5 degrees intake/12 degrees exhaust angles vs. the Gen-IV’s 15-degree angle. Additionally, the valves are splayed
at 2.61 degrees intake/2.38 degrees exhaust to reduce shrouding and enable greater airflow.
Valvetrain components include durable valve springs and roller-pivot rocker arms with a 1.8 ratio – the amount of movement on the valve side
of the rocker arm in comparison with the pushrod side. And speaking of pushrods, the Gen-V small-block features large-diameter 8.7mm
(outside diameter) components that provide exceptional stiffness that enables excellent high-speed valvetrain dynamic performance.
Given the LS4's pressurized induction, special attention was paid on sealing, too. The head gaskets are extra-robust, seven-layer stainless
steel, and the 12mm cylinder head bolts are hardened stainless.