MSD 7562 Programmable Launch Boost Controller Installation - Manual (Page 18)

18 INSTALLATION INSTRUCTIONS
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TEST EXAMPLE 8 - FIGURE 13
This figure is a turbo car with a CO2 controlled waste gate, with a 16-pound spring and about 48psi
on the open side with 90psi on the spring side. This setup was for lowering the spring rate at
launch to about 10-11psi boost, but caused the waste gate to open from the exhaust pressure in
the 7,800-8,150 range when the volumetric efficiency of the engine was at its maximum. It can be
seen that the PWM value drops to near 40 when the pressure began falling but the MSD Controller
could not overcome the exhaust pressure with the combination of the open side pressure and the
spring side pressure. In this case, the spring should be replaced with a 10-pound spring and the
open side pressure lowered to about 30psi or connected to the manifold. The spring side pressure
can then be in the range of 80-90psi to keep the waste gate closed at all rpm. The PID was close to
optimum at 40-40-40 here. The D term could be lowered about 5 for better response and allow the
P to track the target better.
Figure 13