Posted: Wed Jun 13, 2007 12:27 pm
? The minimum boost is determined by the wastegate spring. The boost controller will not be able to reduce boost, but can only raise boost above the minimum level.
? The maximum boost is limited by the exhaust back pressure opening the valve against the wastegate spring, even with no pressure differential on the wastegate diaphragm. The exhaust back pressure increases with engine speed, so it is common to see a drop in boost at high rpm.
? Boost creep is when the boost rises at high rpm despite the wastegate being fully open. Boost creep is caused by using a wastegate valve which is too small, or (more commonly) placing the wastegate off center in the exhaust manifold so that it does not effectively reduce exhaust back pressure from all cylinders.
? A drop in boost at high rpm occurs without a boost controller because the progressively increasing exhaust back pressure open the wastegate earlier as the rpm rises. Changing the position of the wastegate pressure source often eliminates this problem.
? The maximum boost is limited by the exhaust back pressure opening the valve against the wastegate spring, even with no pressure differential on the wastegate diaphragm. The exhaust back pressure increases with engine speed, so it is common to see a drop in boost at high rpm.
? Boost creep is when the boost rises at high rpm despite the wastegate being fully open. Boost creep is caused by using a wastegate valve which is too small, or (more commonly) placing the wastegate off center in the exhaust manifold so that it does not effectively reduce exhaust back pressure from all cylinders.
? A drop in boost at high rpm occurs without a boost controller because the progressively increasing exhaust back pressure open the wastegate earlier as the rpm rises. Changing the position of the wastegate pressure source often eliminates this problem.