There are a couple of different methods of increasing the boost level, from electronic controllers to mechanical bleed valves.
For the SR20DET, the stock T28 turbo can provide boost levels up to about 1 Bar for the CA18DET the stock T25 turbo can provide boost up to about 0.95 Bar. Above these levels the turbos become inefficient and the standard injectors, MAFs and fuel pumps will be near or at 100% capacity.
It should be noted that the stock blow-off-valve (BOV) on the SR20DET won’t hold boost effectively above 1 Bar and can start to open as low as 0.8 Bar. Therefore fitting an aftermarket BOV is recommended for boost pressures above 1 Bar. Also, if you use a manual or electronic boost controller the waste-gate can start to open before the desired boost is reached, this can be solved by fitting a stiffer spring to the waste-gate actuator.
Manual Boost Controllers
Manual controllers are very basic in operation; they bleed off air from the waste-gate actuator pipe causing the waste-gate to open later. The amount of boost run depends on the amount of air bled from the system. Manual boost controllers are cheap and easy to install but they do have their disadvantages. Some can cause boost spikes and boost creep, which is harmful to the engine. They can also cause boost to tail off high in the rev range, which will to affect the top-end power output.
This is a picture of the Forge Motorsport Manual Boost Controller
Here’s the basic setup for a manual boost controller
Electronic Boost Controllers
Electronic boost controllers use stepper motors to control the waste-gate actuator. They monitor boost with an electronic pressure sensor and make adjustments about 10 times a second. Because of this, boost spikes and boost creep are kept to a minimum and the desired boost level is held right through the rev range. Electronic boost controllers are expensive though and have to be fitted correctly else they will not work properly. Examples of electronic boost controllers are: Greddy Profec B Spec II, Blitz AVC-R and HKS EVC.
Here is a picture of the Greddy Profec B Spec II
Aftermarket Waste-Gate Actuator
A 3rd option is to install a different waste-gate actuator. HKS make aftermarket adjustable ones for the S14 which eliminates a lot of unnecessary boost piping within the engine bay and helps increase turbo spool up. Adjustable waste-gate actuators eliminate boost creep and boost spiking and hold boost very well, but they are slightly more difficult to adjust than manual or electronic boost controllers and can’t be adjusted from the cabin.
This is the Forge Motorsport Adjustable Waste-Gate Actuator
