Ghidorah - DOHC L-Series.

The idea of a DOHC L-Series setup is something that has captured the Nissan and Datsun enthusiast headspace since the release of platform. Through the years following only a few ideas have managed to leave the paper they were conceived upon; this is hopefully one of those ideas.

The Rundown

OS Giken

Goerz-Paeco

The Rundown

The topic of designing or retrofitting a DOHC cylinder head to the L-Series platform has been broached by countless people over the years. Some have attempted to capitalise on these widespread desires but production difficulty and the subsequent price tags have reduced a DOHC top end to a pipe-dream for most. OS Giken has reigned supreme for the longest with their TC24-B1 and TC24B-1Z heads but now have to share the limelight with the new DatsunWorks KN20 platform. For the vast majority these options are admirable despite being being prohibitively expensive, leaving little-to-no options left.

OS Giken

The OS Giken twin cam heads first premiered in the late 70's with the release of the TC24-B1. This head boasted a bespoke cast aluminium design, 24 valves, a refined thermostat design, and obviously, 2 cams.

These heads bolt straight onto the L-Series block but require modifications to the timing chain setup as the the placement of the new intake cam is far from the natural chain curvature when running a single central cam shaft. There also appears to be another guide or tensioner bolted to the head. Photos can be viewed here: https://www.tomitaku.com/index_work.html

Some of the defining features of the TC24-B1 head include a single-piece feed-through cam retainers design much like a factory L-Series head as well as screw type valve adjusters.

According to OS Giken, only 9 of these heads were ever made.

The OS Giken TC24-B1Z is a renewed and revised package when compared to its B1 counterpart.

The main differences include a departure from the single-piece cam retainers and screw type valve adjusters. The TC24-B1Z has a large single-piece lower cam girdle and a number of caps to retain the camshafts, much like a more modern setup.

Also similar to modern offerings the B1Z head now utilises a bucket and shim setup, much like an RB (but with less rocker arms.)

It's unclear if these heads will are part of a limited run like the B1's of past but as it currently stands these heads are available to order.

Goerz-Paeco

The Goerz-Paeco cylinder head is the earliest relic of DOHC efforts. This head was purchased at a swap-meet in California sometime in the early 2000's with all tooling required to complete the head and hand drawn schematics for the construction and finishing. The documents pertaining to the construction of this head date it earlier than an the original OS Giken run of TC24-B1's; making this the very first DOHC Datsun L-Series head.

Despite this, no-one knows where this head came from or who made it. Naturally, one would assume that Goerz-Paeco designed and cast the head but Graf Albrecht von Goerz (yes, that Goerz) was contacted directly and claims no knowledge of this head what-so-ever.

The most notible feature is that the head is entirely symmetrical, depending on cam placement, the head would breath either left-to-right, or right-to-left; which sounds exceptionally helpful for engine bay clearance in Left Hand Drive markets where the exhaust and steering components coincide.

Whether the head was a result of clandestine late night sessions once everyone had gone home or died on the drafting table due to bureaucracy, its clear that considerable thought has been put into this piece and ultimately it's a shame it was never finished

The head was listed for sale on eBay in 2014 where the auction was pulled before finishing. The current whereabouts are unknown.

Bryan Blake

The Goerz-Paeco c

Project Ghidorah

Joining the Heads

Oiling

For the longest time I could never understand why Bryan Blake opted to join 3 KA head sections rather than just two. As above, Bryan has the front and rear thirds of one KA head on the L6 block with the remaining middle third coming from the middle of a second KA head; resulting in 2 joins between 3 sections. After beginning my own KA DOHC project I believe I've understood why he opted to construct the head in this manner.

The L6 block has two oiling jets, one at the very front of the block, and a second in between cylinders 3 & 4 on the drivers side of the engine. The KA24DE head also has a middle block jet on the drivers side meaning that it is a bolt on affair when using the L4 block (the front oil jet is not used). Bryan has sectioned his head so that the middle L6 oil jet (in the block) corresponds to the middle gallery in the KA head, the only way to achieve this is to use the middle of the KA head (cylinders 2 & 3) in the middle of the L6 block (cylinders 3 & 4); this leaves him with 2 cylinders to populate at the front and rear of the block respectively, hence the 3 sections.

In my construction, I've chosen to have a singular join between 2 three-cylinder sections. While my oil jets don't line up like Bryan's head, I believe the work involved in joining 3 sections compared to 2 far outweighs the simple solution for no internal block-to-head oil passages. The KA head has very clear embossment on the outside of the head where the oil galleries have been gun-drilled during construction. An external oil line feeding from the block to one of these bosses essentially solves the oiling issue without the need for an additional head section. There are two locations of the side of the KA head that can be fed oil as both of these are exposed to the outside of the head and feed directly into the main gallery. The oil supply can be jetted using the fitting internal diameters, much like an internal oil feed jet operates.

Bore

The chambers on the KA24DE head are 89mm to match the original platform bore. The L6 L28 bore is 86mm from factory which means a total bore of at least 2.5mm is required for the head to be an appropriate application. Having a lip on the top of the cylinder walls will cause issues for the engine due to being a carbon trap, ultimately leading to detonation. Having a reduced bore compared to the head also poses an issue with valve clearance.

An interesting alternative to the KA24DE head is the KA20DE head. The KA20DE has an 86mm bore meaning no boring would be required for use on an L6 L28 block. Obtaining these heads is difficult as they were only sold in the Japanese domestic market.