We’ve been hearing this since SAAB introduced a solenoid controlled boost circuit in the 70s. More recently, the misconception that a manual boost controller is somehow incompatible with “ECU Boost Control” has been growing. We believe this is because as DIY ECU tuning has become more commonplace, many younger tuners don’t realize that the boost solenoid they control through ECU tuning hasn’t changed in 30+ years. It is effectively, the same system used for the last 40 years. When dealing with a non-diesel turbo system, it has always been the case that you “must have enough fuel to prevent a lean condition under boost”. The means to do this were crude in the 1980s, often consisting of dumping too much fuel into the engine, just to ensure you did not go lean. The OEMs had very limited options for alternate ECU programming and aftermarket support was virtually non-existent. Supplementary fuel injector systems were available, but very expensive. Plus 20% injectors and scaleable fuel pressure regulators were other approaches, but without good ECU programming, they were very imprecise. What HAS improved over the years (we’ve been at this since 1986) is the ease of flash programming an ECU and tuning the fuel curve. It’s now relatively inexpensive to change the fuel curve, or to program to a new injector size, allowing an increase in boost. At the same time, we can now alter the boost solenoid control to increase boost through the ECU. In that way, it is easy to raise the boost at the same time you are adjusting fuel maps. ECU tuning gives you the ability to program in complex boost curves, for almost infinite conditions. But, it still has one major limitation—
Manifested in an electronic boost control, hysteresis is a delay in boost response, caused by the feedback loop of the boost control. The feedback loop looks something like this:
The problem with all of this is that it takes time. Even at millisecond processing times in the ECU, it takes magnitudes longer to open and close the solenoid, in order to change the pressure in the wastegate vacuum/pressure line. Add to that the time it takes for the changes to increase or decrease the pressure downstream, at the intake manifold. All of this ends in a situation caused by the system hysteresis—you must start decreasing the rate of boost climb BEFORE hitting peak boost, or you will overshoot the target. Most factory ECUs do this and you can watch it happen as you accelerate. The boost overshoots the target at first and then once the ECU realizes this is happening, it aggressively slows the rate of boost climb. All of this translates to “less area under the boost curve”, meaning, you are sacrificing torque before reaching peak boost in that gear.
If only there was a way to minimize the feedback loop. Enter the manual boost controller. With the right MBC (ball and spring type, not bleed), pressure changes at the turbo can be quickly routed to the wastegate actuator, allowing a fast climb to peak boost, with very little overshoot. The feedback loop is purely mechanical and literally inches long. No sensors located at the other end of the system, feeding back to a solenoid that is also likely to be too small for anything but stock tuning. For full acceleration conditions, nothing can react as fast as an MBC.
Is there a downside to the MBC? Of course—for every Yin, there is a Yang. The downside can be in drive-ability as it is possible to get full boost at less than full throttle. This is generally not noticeable at stock boost levels but the more you raise the boost, the more of an issue it becomes. For this reason, many customers will add a solenoid switch to only activate the MBC certain conditions (racing, impressing your girlfriend, etc.). This activation can be entirely manual, or it can be activated when a certain throttle position or boost level is reached ( 3/4 throttle, or 80% of factory boost peak–i.e., when your intentions are clear). We offer dual stage boost solenoids to do this and well also offer a non-electronic boost controller switches, to turn your manual boost controller on and off. Use the links to check them out and discover what serious racers have known for years, nothing gives more area under the curve than an MBC!