A Rare GemThe legendary heritage of Nissan’s Z is shared with another motorsports legend, OS Giken’s president Osamu Okazaki. Okazaki designed the TC16- MAII cylinder head for the Datsun 510 Blue Bird in the early 1970’s. This cylinder head featured a pent roof-style combustion chamber and four-valves per cylinder. These TC16-equipped Blue Birds were making around 232 horsepower and were practically unchallenged on the streets of Japan. In the late 70’s, Okazaki took it upon himself to improve on the L28 engine of the 280ZX. The performance benchmark of the time was the 1977 Porsche 930 Turbo, and the objective was to improve the L28 to surpass the Porsche’s performance. Okazaki designed a new cylinder head for the L28, dubbed the OS Giken TC24-B1. The total number of heads manufactured was nine. Even so, the heads were sold and promised power was delivered but the comparison between the Z and Porsche didn’t happen. At the time, 930 Turbos were exceptionally rare in Japan, making a heads-up comparison difficult to arrange.
OS Giken’s President Osamu Okazaki humbly reminisces about the TC24-B1 development.
Challenge RevisitedTakuya “Tomitaku” Tomimatsu, one of OS Giken’s top engineers, has a love for the classics; especially the Fairlady Z. Tomitaku uncovered a veritable treasure trove in an OS Giken warehouse, including a forgotten TC24-B1 cylinder head among other L28 racing components. Not long after, he was reminded of Okazaki’s old challenge objectives as he reminisced with classic car aficionados. He then became obsessed with comparing the 930 Turbo to a Z with a TC24-equipped L28. Given the rarity of the challengers, he had his work cut out. After finally locating and restoring a 1979 Porsche 930 Turbo to factory fresh condition, Tomitaku found a 1974 S30 chassis to build upon. He began building his S30 contender in the quest to see the challenge come to fruition.
The TC24-B1-equipped L28 features Ultra CDI ignition coils supplying spark energy to the NGK plugs. Tomitaku fabricated an equal-length stainless-steel header to channel exhaust gasses through a custom exhaust to the rear of the chassis.
OS Giken’s TC24-B1 – Proving That Four Are Better Than Two
Nissan’s six cylinder, 2.8-liter L28 engine came from the factory with two-valves per cylinder and a wedge-shaped combustion chamber. OS Giken’s TC24-B1 cylinder head features dual overhead cams, a pent- roof combustion chamber and four valves-per-cylinder. The volumetric efficiency of four valve-per-cylinder technology along with the pent- roof’s combustion chamber quench pads that improve air and fuel mixing and combustion prove an effective combination, elevating the L28 horsepower output. In Tomitaku’s case, nearly double the horsepower was generated.
S30 Prize FighterTomitaku wasted little time sourcing an L28 block, the cornerstone of the engine bay. A six pack of OS Giken (OS) 12.5:1 compression forged aluminum pistons filled the cylinders while a set of Tomitaku’s own custom-made connecting rods join the pistons to the factory L28 crankshaft. Up top, Tomitaku’s custom-made head studs secure the TC24-B1 cylinder head to the block. Long-duration 320- degree camshafts actuate the valvetrain, making best use of all four valves-per-cylinder and Okazaki’s pent-roof combustion-chamber design.
Weber carburetors mate to the head by way of OS Giken aluminum adapters, while Tomitaku’s custom linkage synchronizes the carbs to a single throttle cable.
Fab FanaticTomitaku’s fabrication ability made the build process much smoother, especially since there are few companies that manufacture performance parts for the L28. Induction duties fall on the shoulders of a set of Weber carburetors synced with custom linkage and a custom fuel delivery system. An Ultra CDI dual ignition system supplies the spark energy to the NGK plugs for combustion. On the exhaust side, Tomitaku designed an equal-length stainless-steel header and exhaust system to channel spent gasses to the rear. When rocking the rollers, Tomitaku tuned the TC24- equipped L28 to a best pull of 325 horsepower.
More Than Just HorsepowerA full complement of OS driveline components harness the power of the refreshed and rebuilt L28 engine. An OS R3A triple-plate clutch mated to the crankshaft transfers power to the input shaft of an OS SR20DET 5-speed close- ratio gearset. A custom propeller shaft turns an OS R180 Super Lock LSD that splits the power between the RS Watanabe wheels. Vintage Nissan “Sports Option” Mk63 4- piston brakes replace the factory pieces for improved braking performance while Energy Suspension bushings and Tokico HTS dampers keep the Yokohama Advan tires planted.
DEFI gauges, including an 80mm tachometer, fit perfectly in the holes and put a modern twist on a classic dash.
Nissan “Sports Option” Mk63 BrakesBefore Nissan Motorsports International (NISMO) ever existed, Nissan performance fanatics had but a few performance options available from the factory. One upgrade was known as the Nissan “Sports Option” Mk63 brakes. These Sumitomo four-piston calipers were the FIA- approved design that could be found on most of the works 240Z and 260Z rallycars, works circuit cars as well as Skyline, Sunny and Violet race cars. The upgraded calipers employ larger brake pads that offer 50% more pad area than the stock units.
The VerdictWith his S30 build completed, Tomitaku finally had the chance to make Okazaki’s personal challenge a reality. He evaluated the S30 and the 930 turbo on the dyno, the drag strip and the street. Tomitaku noted that the S30 bested the benchmark Porsche by 25 horsepower on the dyno and over half-a-second in the quarter mile, validating Okazaki’s design and answering the challenge question. Tomitaku comments, “The built L28 with the TC24-B1 cylinder head exceeded the 3.3-liter Porsche engine output without turbocharging and propelled the S30 down the quarter mile in under 12 seconds. Okazaki-san successfully achieved his goal of beating the Porsche. Admittedly, the 930 turbo is a more refined chassis to drive on the streets, but it is more exciting to drive the Z.” Of the nine TC24-B1 heads that were manufactured, many were raced and have since fallen into the depths of obscurity. Only three functioning examples are known of in Japan and possibly in the world, and Tomitaku is one of the lucky owners. He even maintains the other two, keeping them on the road and the racetracks. He was proud to be able to finally bring closure to a challenge that was posed over 30 years ago, showing Okazaki that he succeeded in his venture. Whenever asked about the challenge outcome, the humble and reserved Okazaki just smiles with a hint of pride.
|Year / Make / Model:||1974 Nissan Fairlady Z|
|Vehicle Weight:||2,156 lbs.|
|Weight Bias (F/R):||51/49|
|Launch RPM:||3,000 RPM|
|Shift RPM:||9,100 RPM|
|Redline RPM:||9,100 RPM|
|Bore & Stroke (mm):||87.8mm x 79mm|
|Peak Horsepower (@ RPM):||320whp @ 7,400 RPM|
|Peak Torque (@ RPM):||246 lb-ft @ 6,100 RPM|
|Pistons/Compression Ratio:||OS Giken 12.5:1 compression|
|Connecting Rods / Crank:||Tomitaku Billet-Steel Connecting Rods/|
|Factory Crankshaft/NISMO Bearings|
|Camshafts:||OS Giken 272-degree, 11mm lift (IN&EX)|
|Valves/Springs/Retainers:||OS Giken Valves, Springs & Retainers OS Giken TC24-B1 Race Head|
|L28 1.2mm Head Gasket|
|Head/Main Studs:||Tomitaku Custom Head Studs|
|Fuel Delivery System:||Weber 2-Barrel 55mm Carburetors (x3)|
|Tomitaku Custom Fuel Delivery|
|Ignition:||Ultra C.D.I. Dual Ignition System|
|Spark Plugs:||NGK-R D9EVX|
|Exhaust Manifold:||Tomitaku Custom Header|
|Exhaust System / Downpipe:||Nagase Engine Works/Tomitaku Custom Exhaust|
|Oil System:||Tomitaku 16-Row Oil Cooler|
|Tomitaku Oil Catch Tank|
|Springs, F&R (Make & Rate):||Nissan Race Springs|
|Shocks, F&R (Make & Rate):||Tokico H.T.S. Dampers|
|Additional Suspension Components:||Energy Suspension Bushings – Full Kit|
|Transmission:||OS Giken SR20 Close-ratio Gearset|
|Transmission Gearing:||2.717, 1.722, 1.232, 1.000, 0.835|
|71B Transmission Case|
|Clutch / Flywheel:||OS Giken R3A Triple-plate Clutch|
|Differential(s) (Make & Type):||OS Giken Super-Lock LSD R180|
|Wheels (Make, Size & Offset):||RS Watanabe|
|15×7-inch (F), 15×8-inch (R)|
|Tires (Make & Size):||Yokohama Neova|
|195/55R15 (F), 215/50R1|
|Brake (F&R):||Nissan Race Option Mk63|
|Roll Bar / Cage:||Cusco 4-point Bolt-in Cage|
|Seats:||Autolook Bucket Seats|
|Hood:||Restored Co. Carbon-fiber Hood|