GM AC251C1 Cylinder Heads Bolt Exhaust 350/400 Heads. 624

( Brand: Gm ), ( Manufacturer Part Number: AC251C1 ), ( Type: Cylinder Head ), ( Oe/oem Part Number: Casting 462624 ), ( Items Included: 2 Remanufactured Cylinder Heads ), ( Material: Cast Iron ), ( Finish: Remanufactured ), ( Country Of Origin: United States ), ( Item Weight: 50 Lb ), ( California Prop 65 Warning: This Product May Contain Chemicals Known To The State Of California To Cause Cancer, Birth Defects, Or Other Reproductive Harm. )

Review GM Pair Of Remanufactured 350/400 Cylinder Heads. Casting#624 Bolt Exhaust fits 350 400

The **GM AC251C1 cylinder heads** specifically designed for the **350/400 cubic inch small-block Chevrolet engines** represent a premium aftermarket upgrade that seamlessly blends performance, durability, and precision engineering. These heads are meticulously crafted to replace the stock cast-iron components, offering a substantial leap in airflow efficiency, combustion chamber optimization, and overall power potential. Engineered with **624 bolt exhaust ports**, these heads feature a **high-flow, high-velocity design** that maximizes exhaust scavenging, reducing backpressure and allowing the engine to breathe more freely. The **AC251C1** designation signifies a refined version of the classic **AC Spark Plug cylinder head**, known for its reputation in the performance community, with enhancements that include **precision-machined valve seats, upgraded valve guides, and a robust bolt pattern** that ensures a secure and leak-free installation. The **350/400 compatibility** means these heads are a versatile choice for everything from **street rods and muscle cars** to **high-performance drag racing applications**, where reliability and power output are critical. Constructed from **high-quality cast iron**, these heads are designed to withstand the stresses of forced induction or high-RPM operation while maintaining structural integrity. The **exhaust port design** is optimized for a **smooth, unobstructed flow path**, reducing turbulence and improving exhaust velocity, which in turn enhances engine efficiency and torque delivery. Whether paired with a **high-performance camshaft, turbocharger, or supercharger**, these heads deliver a **noticeable increase in horsepower and torque** while maintaining a **compact and lightweight profile** that doesn t compromise the engine bay s balance. Additionally, the **624 bolt pattern** ensures compatibility with a wide range of **aftermarket exhaust manifolds, headers, and intake systems**, making these heads a **modular upgrade** that can be tailored to specific tuning goals. For enthusiasts seeking a **direct replacement** that elevates their small-block Chevy s performance without sacrificing reliability, the **GM AC251C1 cylinder heads** stand as a **proven, high-performance solution** that delivers measurable gains in both power and drivability.

### Pros and Cons of Buying GM AC251C1 350/400 Cylinder Heads (624 Bolt Exhaust)

1. **Performance Potential** These heads are designed for high-performance applications, offering improved airflow and combustion efficiency. The 624 bolt exhaust manifold (also known as the "4-barrel" or "high-performance" manifold) is optimized for better exhaust scavenging, which can enhance horsepower and torque, especially in forced-induction or high-RPM applications.

2. **Compatibility** The AC251C1 heads are a common upgrade for GM V8 engines, particularly the 350 and 400 cubic inch small-block designs (e.g., LS-based or older small-blocks like the 350/400 in trucks, muscle cars, or performance builds). They are widely available and have a strong aftermarket support system, including gaskets, studs, and machining services.

3. **Durability** Cast iron heads like these are robust and can handle high compression ratios and aggressive tuning. They are less prone to warping compared to aluminum heads, though they are heavier.

4. **Cost-Effective Upgrade** Compared to full engine swaps or high-end aluminum heads, these cast iron heads are relatively affordable. They provide a significant boost in performance without requiring a complete engine rebuild.

5. **Easy Installation** The heads are designed to bolt onto stock or modified engines with minimal modifications. The 624 bolt exhaust manifold is a direct replacement for many GM applications, though some bolt-on modifications (like exhaust headers) may still be needed for optimal performance.

6. **Proven Reliability** These heads have been used in racing and street applications for decades. Their design has been refined over time, making them a trusted choice for builders looking for a balance of performance and durability.

7. **Versatility** They work well with both naturally aspirated and forced-induction setups (turbocharged or supercharged). The improved porting and valve sizes can handle higher airflow rates, making them suitable for a wide range of engine modifications.

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1. **Weight** Cast iron heads are significantly heavier than aluminum heads. This added weight can reduce engine responsiveness, especially in high-revving applications, and may require additional suspension or drivetrain reinforcement in vehicles with limited payload capacity.

2. **Heat Retention** Cast iron retains heat better than aluminum, which can lead to higher operating temperatures. This may necessitate upgrades to cooling systems, such as larger radiators, upgraded water pumps, or improved oil coolers, to prevent overheating under heavy loads.

3. **Machining Requirements** While these heads are often sold "as-is," they may require porting, polishing, or valve jobbing to unlock their full potential. Some buyers may need to invest in professional machining services, which adds to the overall cost.

4. **Limited Modern Compatibility** Some newer GM engines (especially those with aluminum blocks or advanced fuel injection systems) may require additional modifications or tuning to work seamlessly with these heads. For example, the ignition timing or fuel delivery system may need adjustments to account for the improved combustion efficiency.

5. **Potential for Leaks** Cast iron heads can develop cracks or leaks over time, particularly if the engine is tuned aggressively or subjected to extreme stress. Proper gasket selection and torque specifications are critical to preventing leaks around the head bolts and exhaust ports.

6. **Noise** The 624 bolt exhaust manifold is known for its distinctive exhaust note, which can be loud and aggressive. While this is desirable for performance applications, it may not be suitable for drivers who prefer a quieter exhaust tone or are concerned about noise complaints in residential areas.

7. **Stock Valvetrain Limitations** If the engine retains stock valvetrain components (e.g., pushrods, rocker arms, or lifters), the improved airflow from the heads may not be fully realized without upgrading these parts. A full valvetrain upgrade (e.g., hydraulic roller camshafts, forged valvetrain) is often recommended for optimal performance.

8. **Resale Value** While these heads are great for performance builds, they may not be as desirable in the used market compared to stock or more modern components. A heavily modified engine with these heads may not retain as much resale value as a stock or mildly tuned engine.

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The GM AC251C1 350/400 cylinder heads paired with a 624 bolt exhaust manifold are an excellent choice for enthusiasts looking to significantly boost the performance of their GM V8 engine. They offer a balance of affordability, durability, and proven performance gains, making them ideal for both street and track applications. However, they are not without trade-offs, particularly in terms of weight, heat retention, and the need for additional modifications to fully realize their potential.

For drivers prioritizing raw power, reliability, and a classic GM sound, these heads are a strong upgrade. For those focused on lightweight, modern tuning, or minimal noise, alternative options (such as aluminum heads or different exhaust manifolds) may be more suitable. Ultimately, the decision depends on the specific goals of the project whether it s a high-performance street machine, a drag racing engine, or a restoration with a focus on authenticity and sound.

If you are building a **high-performance GM V8 engine** (especially a 350 or 400 cubic inch small-block) and prioritize **affordability, durability, and a noticeable power increase**, the AC251C1 heads with a 624 bolt exhaust manifold are a **highly recommended upgrade**. Pair them with the following to maximize results:

- A **high-flow fuel system** (e.g., fuel pump, injectors, and a tuned ECU) to support the increased airflow.

- A **performance camshaft** (e.g., hydraulic roller or solid lifter) to complement the improved valve flow.

- **Upgraded valvetrain components** (e.g., forged rocker arms, retainers, and keepers) to handle the stresses of aggressive tuning.

- A **reinforced cooling system** (e.g., upgraded radiator, thermostat housing, and oil cooler) to manage heat retention.

- **Exhaust headers** (if not already using them) to further improve exhaust flow and scavenging.

For **naturally aspirated applications**, these heads will provide a noticeable boost in horsepower and torque, especially when paired with a **high-performance camshaft and carburetor or EFI system**. For **forced-induction builds**, they are an excellent foundation, though additional tuning and support systems (such as a turbocharger or supercharger) will be required.

If your primary goal is **minimal noise or a lighter engine**, consider alternatives like aluminum heads or different exhaust manifolds. However, for most performance-minded GM V8 builders, the AC251C1 heads are a **wise and effective investment**.

Details:

Corvette1975 1982. Compare your heads to these ensure the correct match. CHEVROLET Cars. All seats and surface are re-machined within.e.specifications.

Completely remanufactured SET of TWO cylinder heads. CHEVROLET Trucks Vans. GMC Trucks Vans. Guides are replaced as needed.

FREESHIPPING inside the USA. 1975 1986 SBC 350 400 76cc chamber Cast iron. GM Casting #462624 Complete Vehicle Application List. While the 624 head was used on millions of 350 engines from1975 1987, version with factory-drilled steam holes only fitted to vehicles equipped 400 Small Block, which produced from 1975 to1980.

All heads are vacuum tested to ensure proper valve seating.FREE SHIPPING inside the continental USA only. All bolt holes are repaired as needed. NEW valves, springs, and NEW valve stem seals. All heads are and guaranteed to be free from casting defects.

part #: ac251c1 prices

• $362.50-$1195.00

specifications cylinderheapar:

• for models: 350, 400
• brand: Gm
• mpn: Ac251c1
• type: Cylinder Head
• oe/oem part number: Casting 462624
• items included: 2 Remanufactured Cylinder Heads
• material: Cast Iron
• finish: Remanufactured
• country of origin: United States
• item weight: 50 Lb
• california prop 65 warning: This Product May Contain Chemicals Known To The State Of California To Cause Cancer, Birth Defects, Or Other Reproductive Harm.

offer cylinderheapar:

• quantity: 4
• availability: In Stock
• started: April 7, 2026
• sold: 0
• options: Ship-to-home
• best offers: True

payments cylinderheapar:

• other
• wallet: Google-pay
• credit card: Visa

general cylinderheapar:

• Car Truck Parts Accessories > Engines Engine Parts > Cylinder Heads
• condition: Remanufactured

seller cylinderheapar:

• # reviews: 12
• city: Oakland, California
• rating: 100.0%

returns cylinderheapar:

• policy: No Returns

shipping cylinderheapar:

• transit: 3-9 Days
• class: Standard
• cost: $0.00
• type: Calculated
• service: FedEx Ground / FedEx Home Delivery
• carrier: FedEx

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