[Subscribe to Daily Digest] |
Most DIY MBC's fail to operate well due to the internal spring being too strong and opening too late. If you're DIY MBC only opens at 40psi, your spring is way to strong. The overshoot problem is also due to this as well as the fundemental flaws of all ball and spring MBC's. The NG900/'99 9-3 world has enjoyed the benefits of the MBC+A setup that uses a ball and spring mbc along with a low pressure Air pressure regulator to help prime the line with air so that the MBC can react quicker.
A ball-spring MBC does not flow until the boost pressure is very close to the boost pressure objective (that is the design objective). If the rate of boost increase is slow, there will be no problems. But if the rate of boost is fast, then the MBC needs to get the wastegate open very fast. But it is too late. The MBC simply cannot get the wastegate actuator flow pressurized and flow stroked fast enough, and there is a pressure overshoot. Lightweight balls and springs will not, can not, eliminate this problem!
A ball-spring MBC simply operates too late to regulate the boost pressure when the rate of boost response is fast. We all want fast boost response. The MBC+A overcomes this fundamental flaw in ball-spring MBCs by directly compensating for what the ball-spring MBC cannot do. The MBC+A applies a regulated pressure to the wastegate actuator as the boost pressure is increasing. This anticipates the actuation of the wastegate actuator (WGA). The anticipator pressure is adjusted to pre-pressurize the WGA. This regulated pressure is not enough to open the WGA. Now when the ball-spring MBC starts to flow, its flow can get to the business of stroking the WGA open immediately without delay.
I've got a lot more info if you'd like...
posted by 208.235.174...
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.