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
1	red/white	13.5	170	293.5	136.1	93.10%	111.60%	65.75%
2	white/white	13.5	170	306	136.1	93.10%	116.35%	65.75%
3	yellow/white	13.5	170	300	136.1	93.10%	114.07%	65.75%
4	white/white	13.8	170	306	136.1	95.17%	116.35%	65.75%
5	yellow/white	14	170	300	136.1	96.55%	114.07%	65.75%
6	blue/white	13.8	170	312.5	136.1	95.17%	118.82%	65.75%
7	yellow/white	13.8	170	294.5	146	95.17%	111.98%	70.53%
8	yellow/orange	14.8	170	268.5	196	102.07%	102.09%	94.69%
9	blue/orange	13.9	170	318.5	136.1	95.86%	121.10%	65.75%
10	orange/pink	14.5	170	263	207	100.00%	100.00%	100.00%

Spring Code	Year	Seats	Model	Roof	Engine
1	1984	2	SF/GL	All Roof Type	Non-Turbo
1	1984	2	All Trims	All Roof Type	Turbo
2	1984	4	All Trims	All Roof Type	Non-Turbo
3	1984	2	GLL	All Roof Type	Non-Turbo
3	1984	4	All Trims	All Roof Type	Turbo
4	1985-1986	2	GLL	All Roof Type	Non-Turbo
4	1985	4	All Trims	All Roof Type	Turbo
5	1985	2	All Trims	All Roof Type	Turbo
5	1985-1986	2	SF/GL	All Roof Type	Non-Turbo
6	1987-1989	2	All Trims	All Roof Type	Non-Turbo
6	1985-1986	4	All Trims	All Roof Type	Non-Turbo
7	1984	2	50th AE	T-Top	Turbo
7	1986	2 and 4	All Trims	All Roof Type	Turbo
8	1987-1989	2 and 4	All Trims	All Roof Type	Turbo
9	1987-1989	4	All Trims	All Roof Type	Non-Turbo
10	1988	2	Shiro	T-Top	Turbo

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
1	1 Red / 2 Yellow	12.8	110	364	140	94.81%	114.83%	62.50%
2	1 Yellow / 2 Yellow	13	110	370	140	96.30%	116.72%	62.50%
3	1 White / 2 White	13	110	376	140	96.30%	118.61%	62.50%
4	1 Red / 2 White	13.2	110	382	140	97.78%	120.50%	62.50%
5	1 Red / 2 White	13.2	111.2	382	140	97.78%	120.50%	62.50%
6	1 White / 2 Yellow	13	110	376	140	96.30%	118.61%	62.50%
7	1 White / 2 Yellow	13.2	110	376	140	97.78%	118.61%	62.50%
8	1 Purple / 2 Yellow	13.8	110	336.5	188.2	102.22%	106.15%	84.02%
9	1 White / 2 Yellow	13	111	376	140	96.30%	118.61%	62.50%
10	1 Purple / 2 Yellow	13.8	111.8	336.5	188.2	102.22%	106.15%	84.02%
11	1 Green / 2 Yellow	13.3	111.3	388	140	98.52%	122.40%	62.50%
12	1 Pink / 2 White	13.8	111.8	341	188.2	102.22%	107.57%	84.02%
13	1 White / 1 Purple	13.5	110	317	224	100.00%	100.00%	100.00%

Spring Code	Year	Seats	Model	Roof	Engine
1	1984	2	GL	Hard Top	Non – Turbo
1	1984	All	GL	All	Turbo
2	1984	2	GL	T-Top	Non – Turbo
2	1984	4	GL	All	Non – Turbo
2	1984	All	GLL	All	Turbo
2	1985	All	GL	All	Turbo
3	1984	4	GLL	T-Top	Non – Turbo
4	1985	4	GLL	T-Top	Non – Turbo
4	1985 – 1986	2	GLL	T-Top	Non – Turbo
5	1987 – 1989	All	GL	T-Top	Non – Turbo
6	1985	All	GLL	All	Turbo
6	1985 – 1986	All	GL	T-Top	Non – Turbo
6	1986	2	GL	Hardtop	Non – Turbo
7	1986	4	GLL	T-Top	Non – Turbo
8	1984	2	50th AE	T-Top	Turbo
8	1986	All	All	All	Turbo
9	1987 – 1989	2	GL	Hardtop	Non – Turbo
10	1987 – 1989	All	GL	All	Turbo
11	1987 – 1989	All	GLL	T-Top	Non – Turbo
12	1987 – 1989	All	GLL	All	Turbo
13	1988	2	Shiro	T-Top	Turbo

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.