The JDM CA18DET came with an 8-port head and a lower intake manifold equipped with what Nissan referred to as a “secondary butterflies control system”. Basically, 4 of the 8 ports in the lower intake manifold are equipped with butterflies, which are controlled by a vacuum operated actuator. At lower RPMs, the ECU utilizes an overly-complex system of solenoids, delay valves, tanks and vacuums lines to close the butterflies, which forces all the intake air through only 4 of the 8 ports and increases charge velocity. This results in an improvement in low-end torque and response. The butterflies stay closed until ~3,800 rpm, at which point the “constriction” become inefficient and would cause a drop in mid-range/top-end power.

How much of an improvement the system provides is debatable. I’ve read everything from very little, to as much as a 30-50% increase in low-end torque. Response and drivability are supposed to improve as well. I’ve owned a factory CA18DET powered S13 Silvia in the past. It was a 1990 model, which I bought in 1996 making it a mere 6 years old (yes, I’m old as shit). It was the only CA18 powered car I’ve driven, and it had the OEM butterfly control system in place. So, I don’t even know what it would feel like to drive one without it.

There isn’t a great deal of information about the system out there in English. The UK version of the CA18DET came equipped with a 4-port head and no butterflies. In the USA, the majority are 8-port with the butterflies, but the motor sets were more than likely imported from Japan, and probably didn’t include all the OEM components to properly operate the butterflies. So, the system was either not used at all, or the actuator was simply connected directly to a vacuum port on the intake manifold, which isn’t ideal as ECU has a table that references engine rpm/load.

The best source of info was a a handful of threads on the Australian forum Nissansilvia.com where they referred to them as “power-valves” and dyno charts were shared documenting their performance. Unfortunately all those links are broken now.

Lower intake with butterflies intact (top) and without (bottom)

Unfortunately, while I did have a JDM 8-port head, my butterfly system was removed by the previous owner. This isn’t uncommon as at big power levels the variable intake system apparently provides no benefit, and the butterflies, even when open, cause an impediment in airflow.

With a conservative power goal of only 300-320HP, I felt like getting the system setup and running correctly was worth the effort. After striking out on Yahoo Auctions, I eventually found a mint and fully intact 8-port lower intake manifold from an eBay seller in Greece.

With the complete manifold in my posession, I got to work trying to figure out exactly what I would need to put the OEM system back together. That changed when I came across and very interesting thread on the Nico forums.

A user named “biosehnsucht” had shared his experiences using a Volvo electric power-steering pump in place of the complex factory setup. Instead of a mess of solenoids, delay valves, a vacuum tank, and a bunch of lines to utilize engine vacuum, he ran the butterflies off the vacuum generated by the Volvo electric pump. I was immediately interested and jumped on Ebay and bought a 2000-20004 Volvo V40 electric power steering vacuum pump for a mere $28.

As you can see in the video above, it’s a pretty simple setup. Only a single vacuum line from the Volvo pump to the butterfly actuator is needed. The pump itself only needs 12v constant and ground to run and switched ground (which will be connected to ECU Pin 8) to activate a solenoid inside the pump, which sends vacuum to the actuator and opens the butterflies.

At this point I have the pump working on the bench, but there is still plenty to figure out. I actually ended up ordering Nistune so I’ll be able to edit the factory variable intake table and alter the switching points. Once I have the system operating like it should I’m planning on throwing the Onevia on the dyno so I can document the actual performance benefits (or lack thereof) of the power valves. That includes running them off the Volvo electric pump controlled by the ECU, straight off intake manifold vacuum, and with switching points altered in the ECU table.