BOOST FACTS INDEX
February 2025 | Boost Control Basics (Like, really basic.)
In case you couldn’t tell by the name, we really love boost. It’s that pupil-dilating fairy-dust effect of increased air that creates an efficient and drastic increase in power and acceleration - also known as boost pressure - and often turns a smaller, lighter build package into a predacious powerhouse with greater benefit over cost.
That boost pressure is the amount of air compressed and forced into an engine by a turbocharger (or supercharger - we’ll get to that another time) using exhaust gases from the exhaust pipe to turn the turbine that’s connected to the compressor wheel. But, without regulation, that air running through at nearly the speed of sound can lead to catastrophic engine failure, so it’s necessary to keep it under control. This is why the turbine housing (aka “wastegate”) has a built-in “escape” for excess exhaust pressure.
Exhaust wastegate pressure is a fixed target-pressure in psi/bar used to regulate the flow of exhaust gases to help control that boost pressure, and helps to prevent engine damage while also keeping it running favorably. Excess exhaust pressure is relieved through a flap that is mechanically opened by an arm connected to an actuator that pushes it from pressure applied to an internal weight-rated spring. (Wastegate pressure is also known as “crack pressure,” which is when the target psi/bar is achieved and it “cracks open” the flap.) Said wastegate can either be internal (IWG - single housing), which is your typical factory option that’s more compact, emissions-compliant, limited in output, and budget-friendly, or external (EWG - vents to atmosphere), which is prime-choice for better boost control and greater power, which means greater responsibility, okay Peter? (An EWG can also be designed to recirculate, but is not emissions-compliant.)
Since the one thing controlling the flap is a malleable spring storing mechanical energy that is constantly exposed to different pressures and fluctuations, exhaust pressure can never exceed the spring-pressure, and the turbulence can and will lead to inconsistent target-pressures, potentially causing it to crack prematurely and quash boost pressure. To achieve consistency and even higher boost targets, a boost control solenoid works in tandem to vent pressure away from the actuator, thereby generating accurate pressure targets and even more boost pressure. A manual boost controller (bleed valve) will only get you so far, and a [typically] factory-installed 2-port has limitations, so most builders and high-performance drivers opt in for a 3-port, or even a 4-port electronic boost controller, both of which can be controlled by the ECU based on readings such as: air intake temperature, intake manifold pressure, coolant temperature, vehicle speed, RPM, gear, throttle position, ethanol content, and more. The best thing about a 3-port solenoid, too, is that pressure can be routed directly through the unit to the actuator instead of through a t-fitting, creating better response, quicker spool, and more accuracy.
Additionally, when air is charging through the intake, some of it will bounce back when the throttle plate closes and cause what’s called compressor surge, which means it stalls the compressor wheel enough that it struggles to spool again, or as quickly. To control this, a valve is added before the throttle body to release this back-flow before it can reach the turbo. In most OEM and mid-power builds, a bypass valve (BPV) is added which recirculates that excess air by piping it back in after the MAF sensor, but before the turbo. It’s more reliable with MAF setups, but limited in ability. The other option that higher-output cars use is a blowoff valve (BOV), which vents the excess air to atmosphere. In a MAF setup, the air mass is accounted for and fueling is added, so venting to atmosphere will cause a brief rich condition, which can lead to premature fouling of plugs and cat/s. With speed density, however, it isn’t as affected by this venting phenomenon since it is based on intake temperature, load and RPM. Either way, a BOV will require a precise setup, and it sounds cool, bro.
In short, solenoid goes brrrrrr then air go sssssshhhhh and turbo goes pshew and bov goes pshhhh so driver goes weeeee.
January 2025 | Volumetric Efficiency (VE)
In lieu of painting a Picasso Guernica picture for you, here is our stick-figure explanation: volumetric efficiency is the percentage of achieved air-intake volume in the cylinders of an ICE (internal combustion engine) versus *available* (calculated/theoretical) volume. Naturally aspirated engines typically cap out at 100% (under normal circumstances in an Otto Cycle engine), and anything 80% or higher is considered “good.” However, most of us want our race cars to go-to-11, so we (or some awesome manufacturers from factory) will slap on a forced induction system to compress the air and exceed 100% (as high as 130% or higher) in order to burn more fuel (stick it to the man!) and obtain higher torque and horsepower output at higher loads. Turbochargers are the more popular and efficient choice of forced induction. They use exhaust gas pressure to turn the turbine wheel on the wastegate side (otherwise, this would be wasted in the form of waste-heat energy), which is attached to, and thus turns a compressor wheel in the compressor housing on the intake side, which is where air is - you guessed it - compressed and sent through an intercooler, which helps cool the air before reaching the cylinders. As the air temperature decreases, the air density increases, and the VE goes up, which is why turbos are also known to have even greater effect in colder climates (a.k.a. “turbo weather”).