A Heron cylinder head or simply Heron head, is a design for the combustion chamber

Combustion chamber

A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

s of the cylinder head

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

 on an internal combustion

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 piston engine. The head is machined flat, with recesses only for inlet and exhaust valves, spark plugs, injectors and so on. The combustion chamber itself is contained within a dished depression in the top of the piston

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

. The Heron head is suitable for petrol and diesel engines, for ohv and ohc valve-gear, and for small and large engine displacement capacities.

While it is possible for a flat cylinder head to be combined with simple flat-top pistons, that option ignores the reasons for having a depression in the top of each piston, namely: (i) it provides a compact space for combustion to begin, allowing an optimal flame front; and (ii) it creates significant squish. ("Squish" is an effect in internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

s whereby turbulence is created when the compressed charge is "squished" as the piston reaches TDC

TDC

TDC is an initialism that may refer to:*Hong Kong Trade Development Council*TDC A/S, the largest Danish telecommunications company*TDC, the U.S...

. Such turbulence is desirable as it promotes more extensive mixing of the fuel/air mixture: cf: cf1

Toyota AZ engine

The Toyota AZ engine family is a straight-4 piston engine series. The AZ series uses an aluminium engine block with cast iron cylinder liners and aluminium DOHC cylinder heads. The engine series features many advanced technologies including slant-squish combustion chambers,offset cylinder and...

, cf2, cf3

Chrysler PowerTech engine

The PowerTech was a new engine family for Chrysler, and was not based on the Chrysler A engine as existing Chrysler V8s were. A 4.7 L V8 came first, fitted in the Jeep Grand Cherokee, and a 3.7 L V6 version debuted in 2002 for the Jeep Liberty. The PowerTech V6 and V8 were direct...

).

Pros & Cons

• Advantages include: simplicity of manufacture; compact dimensions; accuracy of the flat machined surface; simplified valve-gear; efficient combustion with good fuel economy.
• Disadvantages include: the greater size and weight of each piston; volumetric efficiency poorer than conventional cylinder heads.

Applications

• Moto Morini 3½ & 500
• Moto Guzzi
• Rover 2000 P6
• Ford Kent engine
• Jaguar V12 engine
  Jaguar V12 engine
  Jaguar V12 piston engine was one of the premier powerplants of the 1970s and 1980s. It was first seen in the Series 3 Jaguar E-type of 1971 and was based loosely on an earlier design intended for a Le Mans car, the ill-fated Jaguar XJ13. The V12 was only Jaguar's second engine design to go into...
  
  
• Volvo 900
• Volvo 700
• Puma racing engines