Reproduction “Shiro Special” Springs

Released as a one-off special edition of the Z31 300ZX, the Shiro Special was a driver focused version designed as a send-off to the Z31 chassis. The Shiro was the final revision among many incremental changes made to the first generation 300ZX, but not much truly distinguished it from the 1988 and 1989 turbo models. Under the hood the Shiro kept the undersized T25 Garrett turbocharger and all of the engine internals of the standard turbo model, but the electronically controlled suspension was (thankfully) tossed in favor of non-adjustable KONI struts, and the rear end sported the unique (to the Z31 anyway) viscous limited slip differential (see my info about the Z31 differential specifications here).

Most importantly, the Shiro Special marked the most aggressive suspension ever built for a Z31 by the factory. To put in perspective the difference between the Shiro’s unique springs and the springs for all other Z31 models, here is a chart showing the comparative measurements for the front springs:

Spring #Color Code
(Top / Bottom)
Wire Diameter (mm)Coil Diameter (mm)Free Length (mm)Spring Rate (lb/in)% Shiro Dia.% Shiro Free Length% Shiro Rate
Shiro springs are bolded
Spring CodeYearSeatsModelRoofEngine
119842SF/GLAll Roof TypeNon-Turbo
119842All TrimsAll Roof TypeTurbo
219844All TrimsAll Roof TypeNon-Turbo
319842GLLAll Roof TypeNon-Turbo
319844All TrimsAll Roof TypeTurbo
41985-19862GLLAll Roof TypeNon-Turbo
419854All TrimsAll Roof TypeTurbo
519852All TrimsAll Roof TypeTurbo
51985-19862SF/GLAll Roof TypeNon-Turbo
61987-19892All TrimsAll Roof TypeNon-Turbo
61985-19864All TrimsAll Roof TypeNon-Turbo
71984250th AET-TopTurbo
719862 and 4All TrimsAll Roof TypeTurbo
81987-19892 and 4All TrimsAll Roof TypeTurbo
91987-19894All TrimsAll Roof TypeNon-Turbo
Reference sheet for spring numbers above

And for the rear:

Spring #Color Code
(Top / Bottom)
Wire Diameter (mm)Coil Diameter (mm)Free Length (mm)Spring Rate (lb/in)% Shiro Dia.% Shiro Free Length% Shiro Rate
11 Red / 2 Yellow12.811036414094.81%114.83%62.50%
21 Yellow / 2 Yellow1311037014096.30%116.72%62.50%
31 White / 2 White1311037614096.30%118.61%62.50%
41 Red / 2 White13.211038214097.78%120.50%62.50%
51 Red / 2 White13.2111.238214097.78%120.50%62.50%
61 White / 2 Yellow1311037614096.30%118.61%62.50%
71 White / 2 Yellow13.211037614097.78%118.61%62.50%
81 Purple / 2 Yellow13.8110336.5188.2102.22%106.15%84.02%
91 White / 2 Yellow1311137614096.30%118.61%62.50%
101 Purple / 2 Yellow13.8111.8336.5188.2102.22%106.15%84.02%
111 Green / 2 Yellow13.3111.338814098.52%122.40%62.50%
121 Pink / 2 White13.8111.8341188.2102.22%107.57%84.02%
131 White / 1 Purple13.5110317224100.00%100.00%100.00%
Shiro springs are bolded
Spring CodeYearSeatsModelRoofEngine
119842GLHard TopNon – Turbo
219842GLT-TopNon – Turbo
219844GLAllNon – Turbo
319844GLLT-TopNon – Turbo
419854GLLT-TopNon – Turbo
41985 – 19862GLLT-TopNon – Turbo
51987 – 1989AllGLT-TopNon – Turbo
61985 – 1986AllGLT-TopNon – Turbo
619862GLHardtopNon – Turbo
719864GLLT-TopNon – Turbo
81984250th AET-TopTurbo
91987 – 19892GLHardtopNon – Turbo
101987 – 1989AllGLAllTurbo
111987 – 1989AllGLLT-TopNon – Turbo
121987 – 1989AllGLLAllTurbo
Rear spring reference

As you can see, the Shiro springs have a significantly higher spring rate, with the rear springs being almost 40 inch pounds stiffer than any other rear spring ever made by Nissan. The reason for this is pretty simple – the Z31 tends to have rear end sag under heavy acceleration, even making stock NA and turbo power numbers. The 300ZX was marketed and designed as a more “comfortable” Z, and the stock springs in the early year Z31s were softer to provide a smoother ride (with the exception of the 50th Anniversary 1984 300ZX). As these springs age, they continue to sag and soften further, and this combined with 40 year old struts leads to many Z31s with poor handling and ride.

Within the Z31 community, the Shiro Special springs were a popular replacement for Z owners looking to get more performance and a stiffer ride from their cars without modifying the suspension. The Shiro and turbo model springs are a direct fit for all Z31s, so the only limiting factor was availability. There were only 1,077 Shiros made for the USA and Canada, meaning Shiro springs were relatively rare even 20 years ago. Today the Shiro springs exist only within forum post mentions and Z31 information sites like XenonZCar, and any examples even in poor condition go for $200+ per half the car. I’ve yet to come across a single listing for Shiro springs that didn’t have “SOLD” attached to it before I could find it, and I searched high and low for a few months.

I was able to procure a set of KONI yellow adjustable struts from Amazon, which are also getting more difficult to locate, but when it came to springs I was completely S.O.L. The Z Store offers an Eibach progressive rate spring kit, but it was unavailable for an extended period of time with the Z Store confirming to me that Eibach suddenly began not including the Z31 spring kit in freight orders, with no planned return date. I see now that the Eibach kit is available, but it is not consistently available and in the future will likely be discontinued.

With no other options, I decided to start from scratch. I created the above sheets, and documented all available info about the OEM Z31 springs. I took that info and reached out to automotive spring and suspension manufacturers, specifically ones located domestically to avoid lengthy import delays due to COVID. I managed to speak to a representative from one of these companies, who informed me they no longer take custom orders (which makes sense, based on their size and manufacturing needs), BUT referred me to three companies who they sub-contract to that did.