1. Cylinder Heads & Parts Engines Components For Sale
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  3. GM AC251C

GM AC251C Cylinder Heads Intake Valve C.i. 2.020 437

fits model: 400.

Ac251c Gm Fully Remanufactured 400 C.i. Cylinder Heads 2.020 Inch Large Intake Valve #437

( Brand: Gm ), ( Manufacturer Part Number: AC251C ), ( Type: Cylinder Head ), ( Oe/oem Part Number: 437 ), ( Items Included: 2 Cylinder Heads ), ( Material: Cast Iron ), ( Vintage Part: Yes ), ( Finish: Remanufactured ), ( Country Of Origin: United States )

Review GM Fully Remanufactured C.i. Cylinder Heads 2.020 Inch Large Intake Valve #437 fits 400

The **GM AC251C 400 cubic-inch V8 cylinder heads** represent a robust and meticulously engineered component designed for high-performance applications, particularly within classic and restored Chevrolet engines from the mid-20th century. These heads are crafted for the legendary **265/283/327/350/396/400 big-block V8** series, offering a blend of durability, reliability, and the potential for substantial power gains when paired with the right modifications. Each head is forged from high-quality **A356-T6 aluminum**, a material renowned for its strength-to-weight ratio, ensuring optimal heat dissipation while maintaining structural integrity under extreme loads. The **400 cubic-inch displacement** designation underscores their compatibility with the larger, high-compression variants of GM s big-block lineup, where they excel in both stock and modified configurations.

A standout feature of these heads is their **2.020-inch intake valve design**, a dimension carefully selected to balance airflow efficiency with the mechanical constraints of the engine s valve train. The larger intake valve promotes improved breathing, allowing for greater volumetric efficiency and smoother throttle response, particularly at higher RPM ranges. This is complemented by the **437-degree valve angle**, a specification that enhances the flow characteristics of the combustion chamber, reducing turbulence and optimizing the mixing of air and fuel for more complete combustion. The valve angle, combined with the precise port geometry, contributes to a **high-velocity airflow** that enhances both low-end torque and top-end horsepower, making these heads ideal for applications ranging from street rods to drag racing setups.

Beyond their aerodynamic advantages, the **AC251C heads** are engineered with practical considerations in mind. The **integrated rocker arm studs** and **precision-machined valve guides** ensure smooth operation of the valve train, reducing wear and minimizing the risk of valve float at high RPMs. The **four-bolt main cap design** (where applicable) reinforces the crankcase, absorbing the stresses of high torque and revving, while the **cast-in oil passages** facilitate efficient lubrication of critical components. These heads are also compatible with a variety of **aftermarket valve springs, retainers, and rocker arms**, allowing enthusiasts to fine-tune their engine s performance characteristics to match specific tuning goals, whether that involves mild street tuning or aggressive forced-induction builds.

For those seeking a balance between performance and authenticity, the **AC251C heads** offer a compelling upgrade over stock components, particularly when restoring or modifying classic GM engines. Their **OEM-style design** ensures compatibility with original engine mounts, manifolds, and accessories, while their **modern manufacturing standards** address common issues found in older heads, such as thin walls, poor casting integrity, or inconsistent machining. Whether used in a **restomod project, a high-performance street engine, or a competition setup**, these heads deliver a proven foundation for building a reliable and powerful V8. With their combination of **aerodynamic efficiency, structural robustness, and adaptability**, the GM AC251C 400 cubic-inch cylinder heads stand as a premium choice for enthusiasts demanding both performance and heritage in their engine builds.

**Pros and Cons of Buying GM AC251C 400 C.I. Cylinder Heads (2.020 Intake Valve, 437 Exhaust Valve)**

### **Pros:**

1. **Proven Performance** The AC251C heads are a well-established design, originally used in high-performance GM engines like the LS1, LS2, and related applications. They are known for their strong flow characteristics, making them suitable for forced induction builds (turbocharged or supercharged) or high-RPM applications.

2. **High Flow Capability** The 2.020 intake valve size and 437 exhaust valve size provide excellent airflow, which is beneficial for engines running at higher power levels. This makes them a good choice for engines with aggressive camshafts or forced induction.

3. **Compatibility with Aftermarket Parts** These heads are widely supported by aftermarket manufacturers, including valve springs, retainers, and seals. They also work well with popular camshafts and intake manifolds designed for LS-based engines.

4. **Durability** The 400 C.I. (Cubic Inch) designation refers to the valve head size, which is larger than stock LS heads, contributing to better heat dissipation and structural integrity under high loads.

5. **Widely Available** Due to their popularity in performance circles, these heads are relatively easy to find, either new from manufacturers like JE or used from reputable sellers.

6. **Good for Forced Induction** The aggressive valve sizes and porting make them a solid choice for turbocharged or supercharged applications, where airflow is critical to preventing detonation and maximizing power.

7. **Potential for Porting** While they are already well-port-ed, further porting can be done to fine-tune airflow for specific engine builds, though this requires expertise.

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### **Cons:**

1. **Cost** These heads are more expensive than stock LS heads, especially when purchased new. Used examples can be found at a lower price, but they may require machining or refurbishment.

2. **Machining Requirements** If purchasing used heads, they may need valve seat machining, valve guide replacement, or deck surface work to ensure proper sealing and performance. This adds to the overall cost.

3. **Valvetrain Stress** The larger valves (especially the 437 exhaust) increase valvetrain stress, which can lead to issues with valve float at very high RPMs unless proper valvetrain components (e.g., heavy-duty springs, retainers, and pushrods) are used.

4. **Head Gasket Compatibility** These heads may require specialized head gaskets designed for high-performance applications to prevent leaks, especially under boosted conditions.

5. **Weight** The larger valve sizes and thicker materials make these heads heavier than stock LS heads, which could slightly reduce high-RPM responsiveness unless balanced properly.

6. **Potential for Overkill** If the engine is not heavily modified (e.g., stock camshaft, no forced induction), these heads may offer marginal gains compared to stock or mildly upgraded heads, making them an unnecessary expense.

7. **Learning Curve for Installation** Installing these heads requires careful attention to gasket surface prep, torque specifications, and valvetrain assembly to avoid issues like leaks or premature wear.

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### **Ending Conclusion:**

The GM AC251C 400 C.I. cylinder heads are an excellent choice for performance-oriented builds, particularly those involving forced induction or aggressive camshafts. Their high flow characteristics, durability, and compatibility with aftermarket parts make them a strong option for engines pushing beyond stock limits. However, they come with a higher upfront cost and require proper maintenance to avoid valvetrain or sealing issues. If your project involves significant power gains (e.g., 500 horsepower with boost), these heads are justified. For mild modifications, they may be overkill and less cost-effective.

### **Recommendation:**

- **Buy them if:** You are building a turbocharged or supercharged LS engine, running a high-performance camshaft, or targeting significant power gains (350 horsepower naturally aspirated or 500 with boost). Ensure you pair them with appropriate valvetrain components and head gaskets.

- **Avoid them if:** Your project is a mild tune or you are on a tight budget, as stock or mildly upgraded heads (e.g., JE 2.020/437 heads) may suffice.

- **Consider alternatives if:** You want a lighter option (e.g., JE 2.020/437 heads with stock valve sizes) or are working with a naturally aspirated engine that doesn t require extreme airflow.

- **Budget for machining** if purchasing used heads to ensure they are in optimal condition for your application. Always source from reputable sellers to avoid issues with cracked heads or worn components.

Details:

Bela Air Full-size sedan 1970 1975 Canada continued1975. FREESHIPPING inside the USA. All heads are and guaranteed to be free from casting defects. Completely remanufactured SET of TWO cylinder heads.

Passenger Cars 1970 1976. Specifications. All seats and surface are re-machined within.e. All heads are vacuum tested to ensure proper valve seating.FREE SHIPPING inside the continental USA only.

Winnebago Chieftain, Brave, Minnie NEW valves, springs, and valve stem seals. Guides are replaced as needed. GM SBC 400 Engines Complete Factory Application List. Heres every factory application, sorted alphabetically by make.

The 400 SBC was produced from 1970 to 1980. Chevalier A-body incl. All bolt holes are retreaded and repaired as needed.

part #: ac251c prices

  • $495.00-$695.00

specifications cylinderheapar:

  • for models: 400
  • brand: Gm
  • mpn: Ac251c
  • type: Cylinder Head
  • oe/oem part number: 437
  • items included: 2 Cylinder Heads
  • material: Cast Iron
  • vintage part: Yes
  • finish: Remanufactured
  • country of origin: United States

general cylinderheapar:

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

offer cylinderheapar:

  • best offers: True
  • availability: In Stock
  • started: April 22, 2026
  • sold: 0
  • quantity: 1
  • options: Ship-to-home

returns cylinderheapar:

  • policy: No Returns

seller cylinderheapar:

  • rating: 100.0%
  • city: Oakland, California
  • # reviews: 14

payments cylinderheapar:

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

shipping cylinderheapar:

  • service: FedEx Ground / FedEx Home Delivery
  • carrier: FedEx
  • transit: 3-9 Days
  • type: Calculated
  • cost: $0.00
  • class: Standard
for models: 400, type: cylinder head, oe/oem part number: 437, items included: 2 cylinder heads, vintage part: yes, finish: remanufactured, country of origin: united states,
category: auto parts > car truck parts accessories > engines engine parts > cylinder heads, material: cast iron, sku: 11963600634968793,
Gm AC251C Is Similar To:
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2 offers $495.00–$695.00 USD
  • Remanufactured. Offer #1 priced at $495.00 + $0.00 shipping estimate = $495.00* total. specifications. NEW valves, NEW springs, and NEW valve stem seals.FREE SHIPPING
  • Remanufactured. Offer #2 priced at $695.00 + $0.00 shipping estimate = $695.00* total. FREE SHIPPING

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