If so, we would like to optimize the water jacket for cooling by providing a sufficient port wall margin while realizing the ideal port diameter and shape with the ideal combustion chamber shape and volume from the beginning. If such a head could be newly designed and manufactured from scratch, wouldn’t it be free from the above-mentioned depression?

The delusion that could be called such a dream story was nothing more than a rice cake drawn in a picture before the gathering of L head project members. Here, I would like to briefly introduce the basics from the start of the project to the completion of the head, and I hope that everyone will warmly watch over this magnificent delusion.

To find the ideal combustion chamber shape and volume while setting the head height to 108 mm, which is the same as the genuine one, the thickness of the upper surface of the head has been increased by 1.2mm while 1.2 mm has been removed off combustion chamber bringing valve closer to the piston side. It has been designed with the common troubles in mind caused by surface grinding, such as ones related to cam chains that often occur due to the usage conditions of various commercially available camshafts.

After analyzing the material of the normal head, we adopted AC4CH for higher strength and durability, and then applied T6 heat treatment.

While forming a big port, the margin thickness to the water jacket is set to 3.5 mm for IN and 3.0 mm for EX (* approximately 2.15 mm only under the IN spring seat), to improve safety against troubles (port wall holes/cracks into water jacket).

The combustion chamber is formed by the latest 5-axis CNC machining, and the shape and combustion chamber volume between the cylinders are the same.

The port core used to form the port during sand casting has been created by 3D printer to achieve a precise and consistent casting surface and high dimensional accuracy.

The diameter of EX port 3&4 has been adjusted to the same size as other cylinders with the aim of making the exhaust flow velocity consistent.

The design of the protrusion, that is caused by the escape part of the head bolt, inside of the port has been changed to a smooth shape during the sand-casting process, and that improves the flow rate.

Engine hanger mounting bolt hole has been created on the manifold side.

Direct ignition coil mount base bolt hole has been created.

A compact combustion chamber is achieved while keeping the standard head height at 108 mm same as the normal N42, which makes it possible to build an engine with a high compression ratio specification without the surface grinding being performed. In addition, the risk of gasket troubles caused by the decrease in head surface thickness is significantly reduced.

By eliminating the unevenness on the top surface of the head as much as possible, the shape is designed so that unnecessary oil pools are unlikely to occur.

After analyzing the water jacket of the genuine head by the detailed CT scanning being performed, a newly designed water jacket takes into consideration efficient and even cooling. The jacket capacity has also been increased by approximately 1.5l, and water channels have been provided in areas where they have not originally existed, enabling even and consistent cooling between cylinders.