SEMA 2009: OS Giken TC24-B1 Twin-Cam L-Series Head


Behold what has been described as the holy grail for Datsun maniacs, the OS Giken TC24-B1! Imagine the sheer mad scientist insanity that must have flowed through Osamu Okazaki‘s brain for him  to conjure up an entire bolt-on twin-cam head, complete with valvetrain, for the Nissan L-series motor.


According to the OS Giken rep at the booth, only nine were ever made, and this one was taken out of a Nissan Fairlady Z in Japan and brought over just for SEMA. Others say that as many as 20 exist.

The TC24 actually originated from the TC16, a twin-cam head for the four-cylinder L-series engines found in Datsun Bluebird 510s. Supposedly, the entire cost of the project was 20 million yen in 1976.

Now, nearly three decades later, they’re thinking of making another run of 10 units or so. Anyone who wants the unicorn of aftermarket Z parts can then do so for the price of a cool $30,000.


The head bumped the L-series’ horsepower output from about 150 to 320. Back in the day, any hashiriya who street raced with TC24-equipped motors were effectively running race engines, which was completely illegal. They lived by the credo, never pop your hood.


Elsewhere at the OS Giken booth was a Superlock LSD made for Nissans rocking R180 rear ends. Combine the two products and you get a one mad Datto.

For more information on OS GIken’s legendary head can be found on

Hat tip to Zack K, who emailed us to say, “Get your asses to the OS Giken booth!”

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18 Responses to SEMA 2009: OS Giken TC24-B1 Twin-Cam L-Series Head

  1. matt says:

    lots of related vids on youtube if you want to hear see and feast:

  2. Bob says:

    Holy flying fuck boats.


  3. robakun says:

    Sean and Mark are da boyz. I used to work with them so know the product well. If you have the ability to buy a new fancy car now, MAYBE they will even sell you one of them TC’s. I saw one running that Tomitaku has in his Z. they rev like a maniac. 10k!!!

    they still have U20 clutches, H190 diff LSD’s, 2TG clutches etc. they are pure old school.

  4. cesariojpn says:

    Reina Akikawa: Devil Z……

  5. zetozeto99 (j.ramirez) says:

    DOES WANT!!!!!!!!!!!!!!!!!!!!!!!!

  6. E-AT_me says:

    i’m a honda guy and never really want to own a datsun, but the car guy in me WANTS THIS.. that is just amazing.. and thank you for the video.. it’s EXACTLY what i need 7AM on a Friday.. who needs coffee? just turn it up loud!!!

  7. Sr-FairladyZ says:

    WHHAAAT??!!! Holy cow! I totally didn’t expect to EVER see a TC24-B1 state side. That’s amazing! I’ve had that “Office Tomitaku” vid in my favorites for some time now. The “Unicorn” is correct since this is as close as you can get to an S20 w/o Yakuza coming after your family lol!

  8. kev says:

    Ooh….OS Giken is making R180 LSDs for the old style diffs?

    This is VERY interesting. Up till now (believe it or not) you can’t get JDM-style LSDs for 240Z, Hako etc without lots of custom work.

  9. Rob says:

    Devil’s Advocate:

    Pisses me off that no one else does this. Muscle car guys have literallly 1,000s of choices for heads for their cars. why doesn’t someone start reverse engineering this and just CNC out a million of them in slightly different spec? Screw OS Giken making 10 more for $30k a piece!!!

    Sorry about the rant and rave but Japanese aftermarket manufacturers downright refuse to make parts people want and need. They’ll spend huge money doing extreme ports and polishes, five angle valve jobs etc when someone could just build a new head. mass produced = cheaper.

    P.S. that head is incredible!

    • Ben says:

      Rob – that is an excellent point. There should be more heads available, but I don’t know if copying OS GIken’s head is the right thing to do. Perhaps they just need a better marketing arm. If they can sell more, I’m sure they would!

  10. Rob says:

    yeah i got carried away with the reverse engineering, stealing a product and its R&D would do nothing toa dvance nostalgics.. but still, everyone else’s cars have choices why do the japanese aftermarket manufacturers ignore the possiblities of new heads for our cars? even honda B-series motors don’t have that many new head choices and those still go for a LOT of money. i guess our sport still has room for growth and that means new possibilities for everyone.

  11. Kev says:

    AFAIK back in the early 80s that OS Giken head was veeeeery expensive. Something like Y1.2mil, which pretty much equates to $30k in 2009 dollars I’d wager. For years, L-series fans pestered OS Giken to re-issue the heads, but OSG would point to the original wooden casting moulds being all busted and aged (with big cracks etc) so reissuing the heads would be more or less starting from scratch, and hey…someone’s gotta pay for all that R&D.

    But to be honest it’s a little bit of bling. The standard L-series head is capable of being worked to flow just as much, if not more than a TC24, so the opportunity cost of a TC24 would always have to be benchmarked against a custom-ported head from a good race shop. OSG can’t compete with that, so they might as well charge a premium to cover their R&D.

  12. HaloZ says:

    When I was walking the floor at Sema I spoted it and i nearly crapped my pants! I got a few pics of it too, but under the plexi. They where very busy when I was at the booth so i didn’t bother them.

    I also spotted the JNC team walking the Honda display on Tuesday.

  13. Rob says:

    hmm..well said. i love this site; learning at work!

  14. Tomitaku says:

    Konnichiwa from Japan, Robakun. Hello, guys. It might be interesting for you to check out my website ( Cheers.

  15. OS Giken says:

    Thanks for the superb article. We were very fortunate to be able to display such a wonderful piece of Datsun history at our booth; to our knowledge it was the first time a TC-24 head was displayed outside of Japan. If anyone is serious about acquiring one of the proposed new units, OS Japan is willing to manufacture them if enough people are ready to put down a deposit. The manufacturing chief mentioned that they need about 25 people lined up to get the ball rolling, and there are already several people ready to pull the trigger on it! At approximately $30-35K it’s definitely not for the meek.

    Regarding the original production numbers, only 9 of the TC-24’s were produced, including the one displayed at SEMA. There were over 20 of the TC-16 heads made, though.

  16. Kevin Truong says:

    That’s one awesome motor!

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