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S13 101: A Primer on the S13 chassis
There were several differnt variants of the S13 chassis in Japan and Australia. This article will help you to decipher the birds and bees... or is it, the Q's and the K's?

There were two main divisions of the S13:

S13: 1988- mid 1990 (which we shall call for this article Version 1)
PS13: mid 1990-1993 (which we shall call for this article Version 2)
Within these divisions, there were two models:
180sx, or the USA Fast Back
Silvia, or the USA Coupe
The 180sx version is identical to the Silvia version of the car in everyway, except that the body is a hatch style instead of a coupe. Nissan denoted this by giving the 180sx chassis an "R" designation. Therefore, RPS13 denotes a Version 2 Fast Back and S13 denotes Version 1 Coupe. Due to the two different Versions, there are also two different engines that came out in each:
1988 - 1990.5: 1809cc CA18DE(T) Engine
1990.5 - 1994: 1998cc SR20DE(T) Engine
The T is in parenthesis for a reason. Some models were NOT turbocharged.

If that wasn't enough for you, there are even more breakdowns based on special options.


Silvia
J's - Base model Silvia
Q's - Middle of the line model Silvia. Full power windows, doors, etc. Non-turbo (CA18DE/SR20DE powered). Optional LSD
K's - Top of the line, turbocharged Silvia. Same power features, etc as the Q's, but came with the turbo variety of the motor. Almost all K's came with LSD's, and it appears to have been a factory-installed part rather than an option.
In addition to the 3 main models, there were two special editions created. First is the Club Series, which would be called a Club K's for example. I have no solid information on what the "Club" spec adds. There are also rumors of an R's and A's series line being produced. However, there is no proof that they even exist, and thus, it is best to rule them out as ever being made as a special edition trim package.
180SX
Type I
Type II
As for what is what, I have no information on this. It appears that nearly all the 180sx's came turbo charged, so perhaps, it can best be compared to a Silvia J's for Type I, and a Silvia K's for Type II, but that is merely my speculation and is not a proven fact.

4 Wheel Steering
Regarded as probably the worst idea in my eyes, several of the early 90s Nissans, Hondas, and Mistubishi/DSM cars were released with four wheel steering. Nissan called it HICAS (HI Capacity Actively Controlled Suspension). HICAS II was released as an option along the CA18-powered Version 1 models, and SuperHICAS was released along with Version 2 SR20-powered models. If at all possible, it is my opinion to avoid this feature. Parts are super expensive, adds almost 20KG of weight to the car, and they are not very reliable.

That just about covers the important stuff from the S13 chassis. There were other options like seats, heads-up display, and so forth that I really don't think are worth mentioning in this article. This is aimed at getting everyone familiar with the terminology of the terms used to define something. So now, when someone posts on our fourms a question such as, "my RPS13 w/ HICAS is having a problem" you know what they are saying.

Information Source: www.nissantech.com