Boost spike is when the initial hit of boost overshoot the target, then comes back down to target number.
I had a bad issue of boost spike with my HDi boost controller, but it doesn't show itself until above 20psi, and higher the boost I run, the higher the spike.
For example, when I set the boost at 24psi, boost would go over 26.45psi then come back down to 24psi and hold it to the redline.
Redline is the boost.
It is usually not an issue, and the spike will actually gives me a higher torque number on dyno.
When I upped the boost, the gap between the spike and the target number got even larger.
Boost went over 29psi, boost then dropped momentary and then held about 26psi to redline.
So, I need fix the boost spike before I can run higher than 24psi to avoid going over 29psi (the limit of my 3 bar map sensor). I gone over my vacuum hose setup and concluded that I need a way to make the wastegate actuator to react faster which can be done by having less air volume between the a solenoid and wastegate actuator.
I put a smaller barb on the boost solenoid/MAC valve, used a smaller vacuum hose from boost solenoid to the wastegate actuator, a barb adapter change the smaller size hose to bigger hose to fit the actuator barb inlet, then make all those hoses as short as possible.
Result was great, no more boost spike!
If you experience boost spike, I would suggest you shorten the vacuum hose from your controller to the wastegate as much as possible, and use a smaller hose.
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