What is a cam-in-block?

A cam-in-block is an engine design where the camshaft sits inside the engine block and operates the valves via lifters, pushrods, and rocker arms, a layout commonly called OHV (overhead valve) or “pushrod.” It’s compact, durable, and still widely used in modern V8s and many truck and racing engines, though it trades some high‑RPM flexibility compared with overhead-cam designs.

How it works

In a cam-in-block engine, the camshaft rotates within the engine block. As the cam lobes turn, they move lifters (also called tappets), which push on long pushrods. Those pushrods lever rocker arms in the cylinder head, opening and closing the intake and exhaust valves against their springs. The timing drive—usually a short chain or gearset—links the crankshaft to the single camshaft.

Key components and the motion path

The motion from camshaft to valve involves several parts that together define the system’s character, efficiency, and reliability.

• Camshaft in the block: One central cam (typically) with lobes that define valve timing and lift.
• Lifters (tappets): Hydraulic or solid components riding on cam lobes; modern versions often use roller tips to reduce friction and wear.
• Pushrods: Slender rods transmitting lifter motion upward to the rockers.
• Rocker arms: Pivoting levers that translate pushrod motion into valve movement.
• Valves and springs: Open to admit air/fuel and expel exhaust; springs close the valves and control motion at high RPM.
• Timing drive: Short chain or gears from the crank to the cam; simpler and generally more compact than multi-cam OHC drives.
• Lubrication: Pressurized oil feeds lifters and rocker arms; oil quality is critical for cam and lifter longevity.

Together, these parts create a sturdy, mechanically straightforward path from the camshaft to the valves, enabling compact engines with strong low- to midrange performance.

Where you’ll find it today

Despite the prevalence of overhead-cam engines in cars globally, cam-in-block designs remain mainstream in North America for trucks, performance V8s, and many racing series. Current examples include GM’s Gen V small-block V8s (LT1/LT2/LT4/LT5 in various applications), Stellantis’s HEMI V8 family (5.7L, 6.4L, 6.2L supercharged), and Ford’s 7.3L “Godzilla” truck V8. Several popular light- and medium-duty diesels (such as the 6.6L Duramax, 6.7L Power Stroke, and 6.7L Cummins) also use cam-in-block architectures. NASCAR’s premier Cup engines remain pushrod V8s by rule, underscoring the layout’s performance potential.

Pros and cons

Advantages

Cam-in-block brings packaging and durability benefits that suit trucks, muscle cars, and endurance applications.

• Compact size and low height: Easier vehicle packaging, lower hood lines, and potential center-of-gravity benefits.
• Simpler timing drive: One cam with a short chain or gears reduces parts count versus multi-cam OHC systems.
• Strong low- and midrange torque: Long intake runners and efficient port designs pair well with cam-in-block for real-world drivability and towing.
• Cost and durability: Fewer cams and shorter timing drives can lower cost and improve long-term robustness.
• Integrated features: Single-cam phasing (VVT) and cylinder deactivation via special lifters (e.g., GM AFM/DoD, Stellantis MDS) are mature and effective.

These traits help explain why cam-in-block engines persist in segments that prize reliability, packaging, and torque over peak-RPM horsepower.

Limitations

Tradeoffs center on high-RPM breathing and advanced valve-control flexibility compared with overhead-cam engines.

• High-RPM limits: Added valvetrain mass (pushrods, rockers) can constrain maximum engine speed and requires careful spring control to avoid valve float.
• Valve timing control: A single cam means intake and exhaust timing move together with phasing; fully independent, wide-range strategies are harder to implement.
• Airflow/valve count: Many OHV heads are two-valve, which can limit peak flow; although modern OHV heads perform well, DOHC layouts more easily package four valves and exotic lift systems.
• Efficiency tech: Variable lift and multi-phase cam strategies are more complex to add to OHV than to OHC platforms.

In practice, modern cam-in-block engines have mitigated many of these issues, but OHC designs retain an edge for extreme RPM and nuanced valve control.

Terminology and variations

Automotive jargon can be confusing. Here’s how the common terms relate, and where older designs fit in.

Cam-in-block vs. OHV vs. pushrod vs. flathead

These labels describe cam location and how valves are actuated, and they’re often used interchangeably—sometimes imprecisely.

• Cam-in-block: The literal description—camshaft located in the engine block.
• OHV (overhead valve): Valves are in the head, actuated by pushrods and rockers from a cam in the block.
• Pushrod engine: Colloquial term for OHV/cam-in-block with pushrods.
• Flathead (side-valve): An older design where both cam and valves are in the block, with no pushrods; largely obsolete today.

Most modern “pushrod” engines are OHV: cam in the block, valves overhead, motion transferred via lifters, pushrods, and rockers.

Lifter types you’ll encounter

Lifters are central to reliability, noise, and maintenance; modern variants also enable fuel-saving tricks.

• Hydraulic lifters: Self-adjusting lash for quiet operation; dominate modern production engines and can incorporate cylinder deactivation.
• Solid (mechanical) lifters: Require periodic lash adjustment; favored in some racing contexts for stability at very high RPM.
• Roller vs. flat-tappet: Roller lifters reduce friction and wear; flat-tappet cams demand correct break-in and oil chemistry (notably anti-wear additives) to avoid lobe scuffing.

The lifter choice affects service needs, friction, and how aggressively a cam profile can be shaped.

Maintenance and reliability notes

Cam-in-block engines are generally robust, but their valvetrains respond directly to oil quality, spring control, and proper setup. Awareness of common symptoms and care practices helps longevity.

Common symptoms and care

Owners and technicians can watch for a few hallmark signs and adopt preventive habits.

• Startup ticking: Brief lifter noise after sitting can be normal; persistent tick may indicate a sticking lifter or oiling issue.
• Intermittent misfire under light load: On engines with cylinder deactivation, a failing deactivation lifter can cause misfires and require replacement.
• Cam/lifter wear: Metallic glitter in oil, loss of power, or persistent valvetrain noise can point to lobe or lifter scuffing—especially on flat-tappet setups with incorrect oil.
• Best practices: Use manufacturer-specified oil viscosity and quality, follow change intervals, and observe proper break-in for new cams (zinc/phosphorus levels are critical for flat-tappet cams).

Addressing valvetrain noise early and maintaining correct oiling are the biggest contributors to long service life in cam-in-block engines.

Summary

A cam-in-block engine places the camshaft in the block and drives overhead valves via lifters, pushrods, and rocker arms. The design is compact, tough, and cost-effective, delivering strong low- and midrange performance and suiting modern features like cam phasing and cylinder deactivation. While overhead-cam systems still lead for ultra-high RPM and independent timing control, cam-in-block engines remain a contemporary, competitive choice in trucks, performance V8s, and racing, balancing packaging advantages with proven durability.

What does a cam do to a V8 engine?

The camshaft activates a cylinder’s intake and exhaust valves. One lobe will activate the intake valve, followed by a second lobe that activates the exhaust valve. As the shaft rotates, the valves will open and close in the appropriate timing.

What does a cam actually do?

The cam actuates rocker arms that press down on the valves, opening them. Springs return the valves to their closed position. These springs have to be very strong because at high engine speeds, the valves are pushed down very quickly, and it is the springs that keep the valves in contact with the rocker arms.

Does a cam increase horsepower?

Yes, a performance camshaft can increase a vehicle’s horsepower by allowing more air and fuel to enter the engine and more exhaust gases to exit, primarily at higher RPMs, through changes in valve lift and duration. However, the amount of horsepower gain varies depending on the specific camshaft, the overall engine setup, and if other supporting modifications are made.
 
How a Camshaft Increases Horsepower

• Valve Lift: An aftermarket camshaft can be designed with higher lift, which is the distance the valve travels into the combustion chamber. This increased opening allows more air and fuel to be drawn into the engine, leading to greater power output. 
• Duration: Camshafts can also increase the duration, which is the length of time the valve remains open. This extended open period gives the engine more time to intake the air-fuel mixture and expel exhaust gases, improving overall engine breathing and power. 
• Powerband Tuning: High-lift, high-duration camshafts are designed to optimize engine performance for higher RPM ranges, resulting in a significant increase in horsepower, especially at the upper end of the engine’s operating speed. 

Factors to Consider

• Supporting Modifications: A camshaft is most effective when paired with other performance modifications that enhance airflow, such as improved exhaust ports. 
• Intended Use: The “right” cam depends on your goals; a cam designed for low-end torque will perform differently than one for high-RPM horsepower. 
• Engine Compatibility: A camshaft needs to be matched to your specific engine and vehicle to achieve the desired results. 

Typical Horsepower Gains
While it’s not a fixed number, typical horsepower gains from a performance camshaft can range from 20 to 50 horsepower, but in some cases, it can exceed 100 horsepower, especially when other modifications are made.

What is the main function of cam?

Its fundamental role is the conversion of rotational motion into linear motion. In internal combustion engines, it is critical for fuel and exhaust management, with the camshaft operating either independently or in coordination with the engine’s crankshaft.