Owner's manual

Grimmspeed

B. Technical Background

A BCS is a binary device – i.e. it is either on (energized), or off. In the context of the

Mitsubishi device, when the BCS is energized, air is allowed to pass through the device, while

when it is off, the air flow is cut.

There are two modes of boost controller operation, at least in this context: “bleed” mode,

which is the mode that the stock BCS operates in, and “interrupt” mode, which is the mode

that a 3-port BCS can operate in. Note that a 3-port BCS can also operate in “bleed” mode,

depending on how it is connected.

Despite being digital in nature, these devices perform a very analog-like task, which is to

control the boost level. In order to do so, the ECU opens and closes the solenoid at varying

speeds, from 0 Hz (closed) to (effectively) ∞ Hz (open).

C. 2-Port Operation (Stock) Review

The stock solenoid is part of the stock bleed-based boost control system. When the solenoid

is off (closed), pressurized air from the compressor is fed straight into the wastegate control.

Any increase in compressor pressure beyond the rated pressure of the wastegate control

results in the wastegate being opened, preventing buildup of boost.

When energized (opened), air is allowed to bleed off the compressor-to-wastegate line by way

of a “T” connector (in stock vehicles, this air is vented back into the intake post-MAF). This

prevents the wastegate from seeing the full compressor pressure, allowing boost to build.

While the stock system operates adequately, it can lead to problems at higher-than-stock

boost levels. Since the bleed system is sized for the stock turbo at stock boost levels, it is

typically incapable of correctly metering air at higher

boost, allowing the wastegate to see pressure and

open before intended. Additionally, since the

wastegate is never completely cut off from seeing

compressor pressure, it can open at low boost levels

and inhibit boost buildup. Ideally, the wastegate

should remain entirely closed for fastest boost buildup

(as all exhaust is then forced through the turbine).

Figure 2: Pneumatic schematic for the GrimmSpeed

Boost Control Solenoid

D. 3-Port Operation and Installation

A 3-port solenoid does away with the bleed-based

system, explicitly shunting air from the compressor to

the wastegate, or compressor to vent (or back into the

intake, OEM-style). Drawbacks of the bleed-based

system are thus eliminated, with the wastegate seeing literally no pressure when the solenoid

is energized, to seeing all of the compressor pressure when the solenoid is de-energized.