TouringBubble
03-05-2010, 10:18 AM
Since the conversation was so good in the chat box, I figured it deserved a thread ...
How a wastegate works
The wastegate is an opening that lets exhaust bypass the turbine, which regulates boost pressure. The wastegate is controlled mechanically by a spring, which may be located remotely (in an actuator like our internal wastegated turbos) or located directly in the wastegate (TiAL, etc).
In our internal wastegate setups, boost pressure is sent to the wastegate actuator and aids in releasing the spring tension, which opens the wastegate and lowers boost. If you send manifold pressure directly to the wastegate actuator, you get what is called "wastegate pressure," or 11.5 psi on the Evo. Wastegate pressure will change with mechanical changes in spring tension on the wastegate actuator.
If you send no boost pressure to the actuator, you basically get the max pressure that the turbo will flow on your setup. The caveat is that the exhaust pressure will usually overcome stock wastegate spring tension at higher RPM, so the wastegate cracks open, further lowering boost and increasing taper. Increasing mechanical spring tension is the only way to keep the wastegate closed in these instances.
How a boost controller works
A boost controller, or any sort, regulates the amount of boost pressure the wastegate actuator receives. As explained above, the more boost that gets to the actuator, the lower the overall boost level.
A boost controller can only work between 0% and 100% duty ... between the lowest and highest boost determined by the wastegate spring. This is why I say that a boost controller cannot increase boost levels, only limit them. A boost controller at 100% duty (fully closed) will produce no more boost than the wastegate can hold.
And MBC and a EBC fulfull this purpose in the same way. The benefit of an EBC is that the solenoid is constantly variable between 0% and 100% duty and can be adjusted "on the fly" unlike a manual controller. A ball and spring MBC works in a similar fashion, but it is limited by the static spring tension the user sets. Basically, as boost begins to taper off, the spring will close off the bypass in the controller to help maintain boost levels, but it can not increase the spring tension past that initial setting, which is essentially what a solenoid could do. So, a ball and spring MBC that is adjusted to maintain a given boost level operates in a smaller duty cycle range, say, 30% to 90% duty (for example) since it will never fully release spring tension and never hold solidly closed.
The "set is and forget it" function of a ball and spring MBC is a great feature. The spring tension in the controller automatically attempts to hold 100% duty on spool up and increases duty as boost tapers. This is somethign that has to be specifically tuned in to many electronic solutions, and it's tought to make an EBC as consistent as a simple MBC. the main benefit of an EBC over an MBC is correction for temperature/elevation changes, assuming the EBC has that functionality.
Please discuss ... we had a great conversation about it in the chat box.
How a wastegate works
The wastegate is an opening that lets exhaust bypass the turbine, which regulates boost pressure. The wastegate is controlled mechanically by a spring, which may be located remotely (in an actuator like our internal wastegated turbos) or located directly in the wastegate (TiAL, etc).
In our internal wastegate setups, boost pressure is sent to the wastegate actuator and aids in releasing the spring tension, which opens the wastegate and lowers boost. If you send manifold pressure directly to the wastegate actuator, you get what is called "wastegate pressure," or 11.5 psi on the Evo. Wastegate pressure will change with mechanical changes in spring tension on the wastegate actuator.
If you send no boost pressure to the actuator, you basically get the max pressure that the turbo will flow on your setup. The caveat is that the exhaust pressure will usually overcome stock wastegate spring tension at higher RPM, so the wastegate cracks open, further lowering boost and increasing taper. Increasing mechanical spring tension is the only way to keep the wastegate closed in these instances.
How a boost controller works
A boost controller, or any sort, regulates the amount of boost pressure the wastegate actuator receives. As explained above, the more boost that gets to the actuator, the lower the overall boost level.
A boost controller can only work between 0% and 100% duty ... between the lowest and highest boost determined by the wastegate spring. This is why I say that a boost controller cannot increase boost levels, only limit them. A boost controller at 100% duty (fully closed) will produce no more boost than the wastegate can hold.
And MBC and a EBC fulfull this purpose in the same way. The benefit of an EBC is that the solenoid is constantly variable between 0% and 100% duty and can be adjusted "on the fly" unlike a manual controller. A ball and spring MBC works in a similar fashion, but it is limited by the static spring tension the user sets. Basically, as boost begins to taper off, the spring will close off the bypass in the controller to help maintain boost levels, but it can not increase the spring tension past that initial setting, which is essentially what a solenoid could do. So, a ball and spring MBC that is adjusted to maintain a given boost level operates in a smaller duty cycle range, say, 30% to 90% duty (for example) since it will never fully release spring tension and never hold solidly closed.
The "set is and forget it" function of a ball and spring MBC is a great feature. The spring tension in the controller automatically attempts to hold 100% duty on spool up and increases duty as boost tapers. This is somethign that has to be specifically tuned in to many electronic solutions, and it's tought to make an EBC as consistent as a simple MBC. the main benefit of an EBC over an MBC is correction for temperature/elevation changes, assuming the EBC has that functionality.
Please discuss ... we had a great conversation about it in the chat box.