When people want to lower their Datsun 240Z / Nissan S30 Fairlady Z, or improve the suspension generally, most owners choose an aftermarket solution. From simple strut damper cartridge inserts with lowering springs, to the recently more popular BC (or other brand) weld-in kits for adjustable-height coilover modifications, a broad variety of options are available. What most owners do not know - Nissan sold its own height-adjustable suspension setup for the S30 range of cars. Time to look a bit closer at that.

Disclaimer
As with all my knowledge articles, I tried my very best to get all information from trustworthy and official sources. However, I cannot guarantee that all information is 100% correct. If you have any correction, input or additional information, I appreciate if you let me know. I’ll update this post whenever I find something to add or change. I am not a professional journalist, but I put countless unpaid hours of work and years of research into this post and spent quite a bit of money to source a lot of original factory documentation, so please ask, before you copy anything. Thank you.

So, what was it exactly? Like the aftermarket weld-in kit's, which are popular today, it is basically a modified standard strut housing which was partially cut off at the top and then a set of threaded cups were welded on instead, where then height adjustable lower spring seats were installed. The kit has to be used with specifically designed springs that came with the kit. The idea behind this kit, is to be able to experiment with different settings without swapping the entire suspension system, and - of course - to be able to adjust the setup to the track's condition.

As the stickers on some of the strut housings, packing boxes (see below), and some of the catalog photos make clear, the suspension was only ever intended for closed circuit racing and not homologated for public-road usage.

Here is my complete setup (note the orange color is not original and somebody repainted it at some point):

In Japan, the competition "Race suspension" was available through the Nissan Sports corner and later NISMO, as shown here in the HS30 sports option parts catalogue:

In the USA, the parts were available at Datsun dealers via the Datsun competition parts, Nissan Motorsports and later NISMO catalogues.

Strut assembly:
The complete strut assemblies consist of the strut housing, modified with the threaded part, the dampers itself with the special nut to secure it inside the strut housing, the top nut and the two lower spring seats. Two pieces to counter-lock them.
54302-E4621, later replaced by 54302-E4622. Strut assembly front right
54303-E4621, later replaced by 54303-E4622. Strut assembly front left
55302-E4621, later replaced by 55302-E4622. Strut assembly rear right
55303-E4621, later replaced by 55303-E4622. Strut assembly rear left

The detailed specifications can be found in the 1986 NISMO catalogue

Interestingly, the SAME catalogue lists the same struts some pages further back with more technical details, but DIFFERENT damping force specifications as shown in the previous photo.
It might be possible that one specification is from the earlier -E4621 variant, or that they got something wrong. I cannot exactly say which specifications are actually correct. 

I have a complete set of the later -E4622 adjustable suspension version, and they came with the early "open" strut damper inserts design. My understanding is that those were put into the strut housings, filled with oil and additionally filled with gas (see later).

Here is a closer look at one of my Aluminum adjustable, threaded spring seats. As you can see in the other photos, the two lower spring seat counter-nuts have different sizes:  Note that the left one in the first picture (with the four notches) is not from this suspension:

Here, a complete setup is shown, including the optional vented MK63 competition brakes.

Springs
While the Struts / Strut housings changed at some point (and went up one part number from -E4621 to -E4622), the springs always remained the same:
54010-E4621 (2x) - front springs
Free length 171,5mm, K*= 3,89, 5,25 coil windings, Length under normal load 120mm, regular load 200kgs

55020-E4621 (2x) - rear springs
Free length 205,5mm, K= 4,83, 5,25 coil windings, Length under normal load 160mm, regular load 200kgs
K = Spring constant (kg/mm)

The detailed specifications are again found in the 1986 NISMO catalogue

I was fortunate enough to find a rare NOS (new-old-stock) original set of springs, still in its original boxes with all the labels on it:

Optional Rear strut spacers
These rear strut mounting spacers are intended to fit the whole adjustable suspension setup correctly in two-seater cars from 1975 model years onwards, and all 4-seater models (2+2 or 2/2) from the beginning.
It is reported that some people might also have used those for experimental setups in earlier cars, and in the front, though.
55037-E4620 (2x), T = 20mm (Listed in Japanese market manuals)
99996-E4060 (2x), 42mm  (260Z 2+2 and all 280Z. Listed in US-market manuals)
The 9999x- part number hints that this was a US-market specific Item, supplied by Datsun USA (and not by Nissan Japan!). It might be that the US-spec cars had a different suspension setup and therefore needed a thicker spacer, hence why a specific US-item with different specification is listed.

Here's a look at my Japanese 3E46220 spacers. Also note that the bigger bores look slightly different in some of the catalogue photos shown on this page. It might be possible that Nissan changed the design at some point.

Since you have to use the whole setup as one, and the strut housings are included, you can use them on any S30 car, despite the originally different strut housing designs in different markets. The kit was never officially sold in any of the Z432(-R) sports option catalogues, but it is known to fit, as we have seen several cars equipped with them. Also, We have seen mix-and-match versions with the adjustable coil overs and long springs from the static setups etc., the spacers used up front, etc. So while it might not have been intended from factory, it does fit.

Nissan used several parallel suppliers for their suspension setup. The ones I have are all engraved / embossed with Atsugi or AMPCO (= Atsugi Motor Corp.), but Nissan also used Tokico for their standard struts, so it might be possible that also a Tokico version of the racing setup exists, as also seen on the works rally "quick exchange" version (see later). Later NISMO replacement dampers were made by KYB (= Kayaba) and are stamped accordingly. See next chapter.
I assume that the number between the Nissan Part number and the manufacturer Logo is some kind of serial number / production date code, but I do not have any details.
On all your strut housings, you should be able to see at least the part number and the manufacturer engraved, as seen in my struts here:

Additional caution and or "Racing only" stickers may also be visible.

Due to the latest available technologies and with the original suspension aging and wearing off, NISMO started to offer replacement parts for the height-adjustable race suspension in the 90ies, as seen here in the 1997 NISMO general catalogue:

The original "open" strut insert design proved to be difficult to service, so Nissan switched to "closed" replacement damper cartridge inserts for the standard 240Z / S30 suspension.
For the adjustable race suspension, such short stroke replacement cartridges were introduced by NISMO, too:
54300-RRE72 = Full set (2x front and 2x rear)
56110-RRE72 = front (2x)
56210-RRE72 = rear (2x)
This is a spare set that I got along with one of my adjustable competition suspension orders with the NISMO numbers stamped on. Not visible in the Picture is the Manufacturer stamp KYB (Kayaba)

In the following photo, you see the complete set:

In the 1997 NISMO general catalogue, the specifications of those "closed" strut inserts can be found:
The specification is similar (but not 100% the same) as the old "open" design inserts.
The text in the catalogue reads:
This is a cartridge type suspension based on the Nissan sports option height-adjustable struts (part numbers 54302/3-E7213 and 5502/3-E7213), with equivalent stroke and damping force. It can be installed in static struts. Please use in conjunction with the corresponding springs (No. 2 or No. 3 in the catalogue). These parts are for racing use only and cannot be used on public roads.

The mentioned part numbers 54302/3-E7213 and 55302/3-E7213 are on which the strut inserts are based on are, however, not from the Adjustable, but from the fixed suspension setup, originally. so I think NISMO mixed up something in the catalogue here. I haven't tried if the strut nserts fit into the adjustable suspension, but my undestading is that they would fit into both fixed-height and height-adjustable struts.

A few years ago, a NOS set of those dampers with the NISMO boxes and installation instructions was for sale in Japan:

The adjustable suspension spring specification remained the same, but the part numbers changed, and an additional set for the NISMO dampers with a static setup was added:

Springs for height-adjustable suspension setup:
54000-E4621 Spring coil kit (2x front & 2x rear)
Equivalent to the old Nissan Sport option springs 54010-E4621 and 55020-E4621. If you compare the data with the previously shown spec, it's almost the same.

Springs for static suspension setup: 
54000-E7211 Spring coil kit (2x front & 2x rear)
Equivalent to the old Nissan Sports option springs 54010-E7211 and 55020-E7211 (for fixed height suspension setup, see HS30 sports option catalogue above)

As noted in the various catalog excerpts in this post, the strut housing was additionally gas-filled. The gas would prevent the oil inside to bubble and foam (and therefore probably lose some of it's intended characteristics) under heavy race use.
The sticker on the struts therefore clearly states that the strut is under pressure and shall not be taken apart nor to apply any heat or fire to it.

If you open the top securing gland nut, the gas will escape, and there is no way to re-fill it without a special setup. In the following photo you can see the special setup used to (re-)fill the gas, provided by Alan:

Some companies also modified the strut housings with drilled holes and added valves to re-fill them without the above setup.

However, if you don't use the setup for professional endurance racing then the struts will most probably also work fine without the additional gas, especially, if you use more modern specified oil for the struts.
The NISMO closed replacement cartridges do not require any additional gas anymore, as they already have an improved closed shock cartridge design

The whole setup is an 1:1 replacement of the original Suspension strut setup. Installation instructions can be found in the Factory service manual.
I checked the Nissan S30 "Race and Rally preparation manual" but the adjustable suspension is not listed or mentioned there specifically. Instead various fixed strut, damper and spring setups for the different cars and the special fixed Rally setup is mentioned.

A special variant of the height adjustable competition suspension was the works racing / rally variant, which was never available for the public to purchase, but only supplied by Nissan to their works teams.
It is based on the same rear strut housing, but with a "quick-exchange" design, where a single nut would hold the strut housing in place and would let the mechanics quickly exchange the rear drum brakes or the struts, in case of damage, malfunction or a different setting needed. The below photos, provided by Alan Thomas, show a photo from the 1971 works team preparing a variety of suspension and brake setups and specific quick exchange struts.

There were most likely many different variants and setups available with different part numbers for different racing conditions. See below photos, provided by Alan, again.
Note the typical red Dymo-labels with the Part number Y2S15-56210 made by Tokico for Nissan (Click pictures to enlarge):

Here, a similar Height-Adjustable setup can be seen on one of the works rally cars:

In the GR(L)S30 260Z 2+2 FIA Homologation, appendix J, you can see that the original -E4621 struts were homologated for those cars. Funnily, the photo of the rear strut shows the "quick exchange" variant, which had a different part number from the one shown in the photo.
Also, it appears that the specific springs, required for this setup, was not homologated specifically.

Always check the part numbers before buying any adjustable suspension setup. Nissan released many similar setups for different cars.
For e.g. the bottom one is not for the S30 but the top one is.

One might argue that with all the modern-day options, this kit is a bit pointless. But if you're into historic racing and need an FIA approved setup, or if your countries government does not accept any modern-day coil overs to be installed in your classic car, then this is the way to go.
But it comes with a big downside: Finding a set is whether cheap, nor easy these days, and most of them are in a well-used condition and need a lot of care. You never know if the dampers and springs are still in a road / track worthy condition, so additional work might be required to get such a setup working flawlessly. Also don't forget that this setup was designed for proper race-usage in the 70ies, so it's a quite hard setup and not really comfortable by today's standards.
But if you have such a rare setup in a good condition, consider yourself lucky to own / drive a cool piece of Nissan / Datsun history. I definitely plan to bring mine back to original condition and have them installed on the car.

Special thanks go out to Chris and Alan with your useful inputs and photos for this post. Kudos!