Cam-in-block engine design is used with overhead valve engines. In this configuration, the valves are actuated by push rods which ride in lifters that follow the camshaft lobes. The camshaft is located within the confines of the engine block, thus the cam-in-block moniker. This technology utilizes a single camshaft along with a single timing chain set and gears. There are two basic choices of camshaft in the cam-in-block engine: flat tappet and roller camshafts.
The choice can be further broken down with the option of hydraulic and solid lifter versions. For the average family sedan, the hydraulic-flat tappet lifter will suffice for most cam-in-block uses. For high-performance engines, solid lifer flat tappet designs were used, such as in the muscle car cam-in-block designs. Racing applications typically rely on solid versions of the roller lifter in cam-in-block engine design. Since the mid-1980s, most cam-in-block engines have used a hydraulic roller cam from the manufacturer.
While most European and Japanese automobile manufacturers have switched to overhead cam style engines, American manufacturers have stayed with the cam-in-block engine design. Ford Motor Company offered a special overhead cam (SOHC) engine in the Mustang in the 1970s. This SOHC engine used a stock cam-in-block engine block with specially prepared hemispherical heads that included a camshaft mounted on each cylinder head. These camshafts were operated by a single timing chain that looped from the crankshaft gear to a special dummy shaft located in the stock camshaft position and then ran to the head mounted camshaft gears. Excessive stretch from the unusually long timing chain made timing the engine very difficult, which led to the engine's demise.
One argument against the block-mounted camshaft in a performance vehicle has always been the loss of power through push rod deflection. The theory is that due to increased valve spring pressures used in high-performance engines, the push rods are thought to bend and flex slightly at the upper limits of the engine's operational peak, which results in lost power because the valves are not opening as far as they should. With an overhead cam engine, the camshaft actuates the valves, eliminating the push rods. No push rods means there is no deflection to rob power.
When faced with this argument, top engine builders favoring the in-block design are quick to point out an interesting fact. The most powerful piston engines in the world are nitro-methane powered Top Fuel dragsters. These engines produce more than 5,000 horsepower; these engines are also cam-in-block type engines.