This is the first generation CA18DET head and intake manifold design. It was used on the J-Spec MK2 S12 Silvia, U11 Bluebird, and maybe the early U12 Bluebird's as well until it went to a top mount intercooler and the 2nd gen head/manifold/etc. (A comprehensive list of chassis and chassis codes would be helpful here)
As you can see, the intake manifold is completely different than the more common, later model intakes. This setup is fed pressurized air from the turbo outlet, NO INTERCOOLER, directly over the valve covers, and into the throttle body, much like the RB25DET setup. But the main difference you'll notice, is that if you look closely, there are 4 large runners, that split about where the manifold bolts together into 8 runners, 4 large diameter runners that have a short path to the head, and then 4 more, long, skinny runners that run down, and then back up into the head. This system works by closing off the short, fat runners are low load/rpms with butterfly valves near the head. This forces the air to take the path through the long, skinny runners that feed only 4 of the intake valves (one per cylinder). This will be easier to understand in the next 2 photos.
Here you can see better how the system works. Unlike the later 8 port setups, all 8 ports are either closed, or partially blocked off at low load/RPM. The ports that are only partially blocked off are fed air by the longer, skinnier runners all the time. These are also the runners that the fuel injectors are placed on. Another thing to note is the difference in the fuel injectors. Although they're a top feed, they are a very odd style. Trying to get uprated injectors for this setup would be very difficult and would probably require fabricating a new fuel rail to accommodate new style injectors.
Another bit of information is that this version does have piston squirters like all of the later models with turbos (I don't think any of the N/A models had them), but DOESN'T have the crank girdle that all of the turbo models had (this was also left out on the N/A models as well). This could be updated with those parts, but would require the girdle, main bolts, and oil pickup from another engine.
It's also important to note that the New Zealand destined U11's didn't have any idle control equipment, as the emissions requirements were quite lax at the time.
On to the later model 8 port CA18DET. This was used in the later AWD Bluebirds that were intercooled, the RWD Silvia's and 180sx's, and the Pulsar's in the US. (A comprehensive list of chassis and chassis codes would be helpful here).
Here is a picture of the head. The difference in the ports is clear. The high load ports don't seem to change much, if at all. The low load ports are vastly different. The main difference being that none of the port is blocked at low loads. The next image clearly shows why.
Here you can see that there are now only 4 valves in the manifold. The 4 valves that have the fuel injectors in them are always open. It's also important to note that this system "fails safe", meaning that if there is a loss of vacuum, the valves open. I don't know if this is true for the 1st gen system, but I would suspect it works the same way.
Another difference to note is that Nissan now introduced what is refered to a a "sub" or "lower" manifold that was different between the 2nd gen 8 port head and the 4 port head, but both used the same upper manifold. The upper manifold (or plenum in other countries) was the same for FWD and RWD layouts. The manifold was designed in such a way that the Throttle body could be bolted to either end of the plenum, allowing it to work for either layout.
Here you can clearly see the 8 port manifold bolted to the common plenum. This is the orientation for FWD.
Before moving onto the 4 port, I feel like I need to bring the CA16DE into the mix. Although this motor is rare, it's relevant due to it being sold in the US, even if it was only for one year. Concrete data is hard to find on this motor, but from what I understand, the head isn't exactly the same as it's CA18DE(T) brother. The intake and exhaust ports are the same, but the size of the valves and the size of the combustion chambers were different. (THIS NEEDS CONFIRMED OR DENIED). It was also equipped with an EGR system. It also used the lower/sub manifold like it's CA18 brother, but it wasn't identical. There was a coolant port that passed coolant to the upper manifold/plenum that's not found on the CA18's. What's interesting is that Nissan didn't change the gasket when they dropped the CA16 and so the seal for the coolant passage is still present in all of the 2nd gen CA18 upper to lower gaskets. Another difference to note is that the CA16 used an "over the top" manifold design, similar to the 1st gen CA18's, but didn't have the more complicated manifold and port design. The following picture illustrates these differences.
Thanks to Livelyjay, I've learned that this intake manifold design wasn't exclusive to the CA16DE. It was also used on all the USDM N13 (Pulsar) CA18DE engines as well.
Lastly is the 4 port head. This was an alternative head design used mainly in Europe. The theory for the difference in the design is that the Europeans didn't have the same need for low end torque as in other pars of the world, and that they were more interested in higher speed driving (such as the Autobahn). The 4 port head allowed for easier breathing at higher RPM's and loads.
This image illustrates the difference in the design of the head. Clearly this head uses a more common 4 port design.
Here you can see the difference in the lower manifold.
By 1991 Nissan discontinued production of any of the 8 port CA18DE(T)'s. Nissan continued to use the 4 port CA18DET in Europe until the S13 chassis was replaced with the S14 chassis in 1995.
Any questions, commments, pictures, or information would gladly be welcomed.
