Some engines, particularly medium- and large-capacity diesel engines built for industrial,

marine, power generation, and heavy traction purposes (large trucks, locomotives, heavy

equipment etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a

single failed head on a single cylinder can be changed instead of a larger, much more expensive

unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a

'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder

head designs.

The design of the cylinder head is key to the performance and efficiency of the internal

combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a

lesser extent the exhaust) determines a major portion of the volumetric

efficiency and compression ratio of the engine.

Automotive 4-Stroke Engine Head Designs - Valve and Camshaft Configurations

Common

NamesCamshaft

Intake

Valves

Exhaust

ValvesNotes

Double

Overhead Cam

DOHC

Head Head Head

Allows optimum positioning of the valves for

a cross flow cylinder head.

Double camshafts are used to allow direct

actuation of well-placed valves, without

rockers.

Widespread in modern car design

Overhead Cam

OHCHead Head Head

Widely used for cars in recent decades, but

increasingly superseded by DOHC.

Overhead Valve

OHV, I-Head,

Pushrod

Block Head Head

Still used in big V8 pushrod engines

Needs pushrods and rockers to actuate

valves

Sidevalve

Flathead, L-

Head, T-Head

Block Block Block

Once universal, now obsolete

Simplest possible configuration

Cams operate directly on the valves

Inlet-Over-

Exhaust

IOE, F-Head

Block Head Block Always uncommon, obsolete for decades

TYPES OF CYLINDER HEADS:

FLAT HEAD ENGINE CYLINDER HEADS:

This engine head design became common in early engines due to its simplicity. It featured the

valves themselves built on sides of the cylinders rather than in the top section, with the lower

part of the head containing chambers for the valves to rise into to enable intake and exhaust.

The head was essentially a single slab of metal without any mechanical parts, which made its

manufacturing and assembly easy. This design also offered simpler and better cooling

mechanisms, but eventually lost popularity due to severe performance limitations as the

airflow required a 90-degree turn to enter the combustion chamber resulting in inefficient

compression and poor combustion. Similarly, another drawback is the complicated exhaust

path, leading to overheating of the engine by keeping the exhaust gases within it for a longer

duration.

OVERHEAD VALVE (OHV) ENGINE CYLINDER HEADS:

These engine head designs are found in engines with cylinder blocks containing the camshaft. The head features intake and spark mechanisms as well as the valves, which are actuated for