What small block Chevy aluminum heads do

Small block Chevy aluminum heads replace the cast iron heads that came on most small block engines from 1955 onward. They bolt onto the same engine block and connect to the same intake and exhaust manifolds, but they weigh less, cool faster, and allow higher compression ratios because aluminum conducts heat away from the combustion chamber more efficiently than iron.

The trade-off is cost: aluminum heads run $800 to $2,500 per pair depending on the casting quality and port design, while used cast iron heads might cost $200 to $600. Aluminum also requires more careful maintenance — you cannot use certain coolant additives, and you need to torque bolts to exact specifications to avoid warping the softer metal.

Most people choose aluminum heads when rebuilding an engine for performance, or when an original cast iron head has cracked beyond repair. They are not a bolt-on upgrade for a stock engine unless you are also changing the intake manifold and fuel system to match the new head design.

Key Takeaways

  • Aluminum heads weigh 15 to 20 pounds less per pair than cast iron, which reduces overall engine weight and can improve handling in lighter vehicles.
  • Aluminum conducts heat faster than iron, which means combustion temperatures stay lower and you can run higher compression ratios without detonation.
  • Most aluminum heads require a different intake manifold than original cast iron heads because the bolt pattern and port shape changed.
  • Aluminum heads cost significantly more upfront but can support higher horsepower and RPM limits if the rest of the engine is built to match.
  • Cooling system maintenance matters more with aluminum — use only coolant formulated for aluminum engines and follow torque specifications exactly.

Common aluminum head designs for small block Chevy

The most common aluminum heads are the Edelbrock Performer and Performer RPM series, which fit 1955–1986 small blocks and use the original intake bolt pattern. These are popular because they work with stock intake manifolds and require minimal modification to existing engine bays. The Performer line runs roughly $1,000 to $1,400 per pair.

The Chevrolet Performance LS3 style heads are newer and designed for modern small blocks, but they require a complete engine swap because the bolt pattern, valve cover location, and accessory mounting are completely different. These are not a retrofit option for a classic small block.

Brodix and World Products make high-end racing heads with larger ports and better flow characteristics, designed for engines over 400 horsepower. These run $2,000 to $2,500 per pair and are overkill for a street engine or mild rebuild.

Used aluminum heads from the 1990s and 2000s sometimes appear on the used market, but inspect them carefully — cracks in aluminum are harder to see than in cast iron, and a cracked aluminum head cannot be welded reliably.

Intake manifold compatibility and port matching

The intake manifold bolt pattern changed several times across small block history. Original cast iron heads use a spread-bore pattern, while many aluminum heads use a square-bore pattern. If you install square-bore aluminum heads on an engine with a spread-bore intake, the ports will not line up and you will have vacuum leaks and poor performance.

Before buying aluminum heads, confirm the intake bolt pattern of both the heads and your current manifold. If they do not match, you will need to buy a new intake manifold — another $300 to $800 depending on whether you choose cast iron or aluminum.

Port matching means grinding the intake and head ports so they line up perfectly. Even a small gap between the manifold and head port can create turbulence and reduce airflow. Many machine shops offer this service for $150 to $300 per head, and it is worth the cost if you are building an engine for performance.

Installation and torque specifications

Aluminum expands and contracts more than cast iron as temperature changes. This means head bolts can loosen over time if you do not follow the correct torque sequence and specification. Always use a torque wrench set to the manufacturer's specification — typically 65 to 75 foot-pounds for small block Chevy head bolts, but check your specific head casting.

Tighten bolts in a cross pattern, starting from the center and working outward, rather than going around the perimeter. This distributes clamping force evenly and prevents warping. Many builders re-torque aluminum heads after the first 50 miles of driving to catch any settling.

Gasket choice matters too. Use a multi-layer steel (MLS) gasket rather than a traditional cork or composite gasket, because MLS gaskets seal better against aluminum and resist the movement that aluminum heads experience. An MLS gasket costs $40 to $80 per pair but lasts longer and leaks less often.

Cooling system changes you may need

Aluminum heads transfer heat to the coolant faster than cast iron, which means your cooling system must handle the increased heat load. If you are upgrading from cast iron to aluminum on an older engine, check whether your radiator and water pump can keep up. A marginal cooling system that worked fine with cast iron may overheat with aluminum heads.

Use only aluminum-safe coolant — typically a long-life organic acid technology (OAT) or hybrid OAT formula. Never use old-style green coolant with silicate additives on aluminum heads, because silicates can form deposits that clog cooling passages and cause localized overheating. Drain and flush the entire system before switching to aluminum-safe coolant.

Some builders add a coolant bypass hose from the head to the water pump inlet to improve circulation through the heads. This is optional for street engines but common in racing builds where every degree of cooling matters.

Performance gains and limitations

Aluminum heads alone do not add horsepower — they enable it. A stock small block with aluminum heads bolted on will not run faster or stronger than it did with cast iron. The gains come from the combination of aluminum heads, a higher compression ratio, better fuel, a tuned intake manifold, and an optimized ignition curve.

A typical street rebuild with aluminum heads, a mild cam, and port matching might gain 30 to 50 horsepower over a stock cast iron engine. A full racing build with high-flow aluminum heads, a larger cam, and a performance intake can gain 100 horsepower or more, but that requires changes throughout the engine and fuel system.

Aluminum heads also allow higher RPM limits because they cool better and support higher compression. A stock small block is limited to around 5,500 RPM safely, while an engine with aluminum heads and a reinforced bottom end can turn 6,500 to 7,000 RPM without detonation.

Frequently Asked Questions

Can I use aluminum heads on a 1970s small block without changing anything else?

Not without issues. You will need to check the intake bolt pattern and likely buy a new intake manifold. You should also upgrade to aluminum-safe coolant and use an MLS gasket. The heads themselves bolt on, but the supporting systems need attention to avoid leaks and overheating.

What is the difference between Edelbrock Performer and Performer RPM heads?

The Performer RPM has larger ports and better flow characteristics, designed for higher RPM and higher horsepower engines. The standard Performer is adequate for street engines and mild builds. RPM heads cost $200 to $400 more per pair but are unnecessary unless you are building for 400+ horsepower.

Do aluminum heads crack easily?

Aluminum is softer than cast iron and can crack if you over-torque head bolts or run the engine too hot. However, quality aluminum heads from established manufacturers are engineered to handle normal use. Avoid cheap import castings and follow torque specifications exactly.

Can I weld an aluminum head if it cracks?

Aluminum can be welded, but the repair is difficult and often unreliable because the weld does not bond as strongly as the original casting. Most machine shops recommend replacing a cracked aluminum head rather than attempting a weld, especially if the crack is near a combustion chamber or water passage.

How much weight do aluminum heads save compared to cast iron?

A pair of aluminum heads weighs roughly 15 to 20 pounds less than cast iron heads. On a full engine, this is a modest weight savings, but it reduces the center of gravity slightly and can improve handling in lightweight vehicles or race cars where every pound matters.