The Cylinderhead is one of the main components that make up the engine.

The Cylinderhead forms the top of the cylinder and houses the sparkplugs, valves and the mechanism to operate them in the correct order and at the right moment. Togheter with the cylinderblock and the oilpan it forms almost the entire engine (Without considering internal and external parts). The cylinderhead is cast out of a aluminium alloy, which makes it nice and light.

The cylinderhead of my 4A-GE  engine, just after disassembly.

In this pictures, you can still see the top of the valve stems and springs. The headgasket lies next to the head.

To make sure that the cylinderhead forms an airtight seal with the cylinderblock, a headgasket is used which is sandwiched between the two parts. Both mating surfaces are machined to be perfectly flat so that a good seal can be formed.

The cylinderhead is one of the most important parts of the engine that determen the performance. The cylinderblock can be as strong and good as you can make it, if the disign of the cylinderhead isn't good, the engine will not perform.

The cylinderhead forms the entrance for the air to come into the cylinders, and determens how much air can be sucked into the cylinders and how this is done. It also forms the exit for the exhasut gasses and again determens how this is done.

The picture above shows a cut through of a 4A-GE 16V cylinderhead. In this picture you can clearly see the in- and- exhaust valves and the valve seats. The yellowish, cut in half cylinders you can see here are the bronze valve guides. These bushings are fixed in the head by means of a shrink-fit.

The head is also one of the parts that form the combustion chamber.The combustion chamber isn't a part you can really  point out to someone because it is made up of several parts. If have written a article dedicated to the combustion chamber, so if you want to know more about that subject, then please read that article to. For as far this all relates to the head, the picture below might help visualize things a bit:

As you can see in the picture, the part with the valve seats forms the top of the combustion chamber. The valves are situated at an angle to each other. This is one of the things that can determine the characeristic of the engines power output. The valve angle of the 4A-GE is set at about 45°. This is also the main difference with other head designs in the 4A- engine family.

At the time that the 4A-GE was made, the  populair believe was that larger valve angles made bigger power at naturally aspirated, high revving engines. With modern day technology, airflow into the cylinders can be better controlled with smaller valve angles. Most modern racing engines use very small valveangles. But hey, a large valve angle certainly worked for the 4A-GE!

There is a lot more to the cylinderhead than is written in this article. But a lot of that can be read in other articles about parts of the cylinderhead. I would like to refer you to the articles about the camshafts, valves, valveguides, combustion chamber, etc, etc that can be found on this website.