Boost Spike, issue fixed for good!

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.
http://www.thelostartof.net/tryingbe...boostspike.jpg

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.
http://www.thelostartof.net/tryingbe...ostspike29.jpg

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!
http://www.thelostartof.net/tryingbe...st%20spike.jpg


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.

been trying to get this idea across for years. This applies to all vac/pressure lines. SHORT AS POSSIBLE!!!! There's a reason new cars have the MAP bolted directly to the intake! But no, people think it's a great idea to bolt on a big old Ford Vac block and have a whole bunch of hoses going all over.


Here's my T2 boost control line set up for minimum boost. When I want more boost I take the plastic line out and install my grainger valve in it's place.

https://scontent.fsnc1-1.fna.fbcdn.n...8d&oe=5ADFA434

https://scontent.fsnc1-1.fna.fbcdn.n...e0&oe=5ADE1B06

Tryingbe,
Very interesting, Short as possible makes sense. What is the ID of the line you finally selected?

That is good advice Harry.
Sometimes common knowledge isn't so common.

Quote:

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Originally Posted by chromguy

What is the ID of the line you finally selected?

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3 mm inner diameter

Something to consider also, are you sure your spike wasn't over 29psi? If you are only 3 bar that is about the limit of your range anyway.
Have you considered gojng 4bar yet?

Quote:

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Originally Posted by wheming

Something to consider also, are you sure your spike wasn't over 29psi? If you are only 3 bar that is about the limit of your range anyway.
Have you considered gojng 4bar yet?

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I'm sure it spiked over 29psi.

Nope, not going to 4 bar map sensor. The car already has much more power than I can ever used on the street, no reason to spend another $1500 (injectors, map, turbo) to make more power that I cannot use. My current setup works very well as a package.