If you’re a Japanese performance enthusiast, or a regular reader of NZ Performance Car, the name ‘OS Giken’ will be one familiar to you. While you’ll probably be familiar with the clutches and LSDs bearing the legendary OS Giken name, that badge has been around for a whole lot longer.

In the 1960s, Osamu Okazaki decided to build upon his passion for performance, and began building high-performance Japanese race engines. While he started out working on motorcycles, his development evolved into automobiles, and OS Giken was born in the 1970s. 

Perhaps that motorcycle history is the reason why one of the finest pieces in OS Giken’s history is a cylinder head for the venerable Nissan L-series of engines. This kicked off in 1974, when OS Giken released the TC16-MA2 — a double-overhead cam head designed for the L-series four-cylinder powering the Nissan Bluebird 510s of the time. With four valves per cylinder, aggressive camshaft profiles, and Weber DCOE carburettors taking care of the breathing side of things, and a built, high-compression bottom end, the little 1.8-litre race engines were capable of producing in excess of 230hp — incredible for the time, and quite an achievement even now. 

The TC16-MA2 was further developed upon when Osamu Okazaki developed the TC24-B1 — essentially, a six-cylinder version of the same, race-developed head. Four valves per cylinder, twin cams, and pent-roof combustion chambers all contributed to a naturally aspirated power figure of more than 320hp — nearly double the output of the factory L28 engines. 

These cylinder heads are the rarest of rare things in the automotive aftermarket world, and command prices to match — if you can even find them. But, recently, OS Giken have been making waves with a newly developed and redesigned version of their TC24-B1 cylinder head, named the TC24-B1Z. It was first revealed at the SEMA 2013, and was said to allow the worked L-series to rev to 10,000rpm, and produce in excess of 400hp, naturally aspirated.

Is this redesigned piece of JDM aftermarket history actually going to see mass production? Unlikely, but for now, you can at least enjoy the sweet sound of a TC24-B1Z–equipped 240Z on the road in the video below — turn the volume up.