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Old 04-20-2010, 04:45 AM   #1
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Default Help me understand this boost spiking problem (not miata related)

All right guys.

I have friends that own Mazdaspeed Protegé. Many of them have spiking problem. They take their signal for MBC/WGA on the pipe after the intercooler.
Now one of them tried to get the signal at the nipple on the turbo and he says that solved the problem.

Now if I read correctly this thread: https://www.miataturbo.net/diy-turbo-discussion-14/suppose-i-fed-up-boost-drop-off-32479/ it should not work in theory. I mean, taking the signal at the turbo doesn't change thing and in fact it should make it worst in adding boost drop because of the intercooler. Now they keep saying that having a shorter hose for the MBC/WGA is what solve the problem because the signal is getting to the WGA faster, but I just can't believe it. And they don't have boost drop.

I poped the idea that now that the signal is on the turbo that the IC could "absorb" or "hide" the spike but they don't buy it (I don't myself, but it's just an idea) .

My brain is trying to solve this puzzle but it just can't alone.
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Old 04-20-2010, 07:44 AM   #2
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By moving the source from one side of the intercooler to the other, the wastegate can no longer sees the pressure drop across the intercooler (the more airflow, the greater the pressure drop, not to be confused with the total pressure).

This basically means that the wastegate can is seeing a more constant pressure, instead of target pressure in lower rpms, then less than target pressure as rpm and airflow increases, which closes the wastegate and produces the resulting overshoot/spike.
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Old 04-20-2010, 09:57 AM   #3
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It's the pressure drop through the IC.

When the signal is taken post intercooler, the turbo is free to spool until the pressure reached the signal source. Chances are there is more boost pressure before the IC than after, so if they are running high boost levels there is a chance that it might make a brief boost spike before the pressure reaches the wastegate.

Sourcing the boost at the turbo will slow the response because there is more boost pressure, faster, reaching the wastegate to control/slow the spool.
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Old 04-20-2010, 10:51 PM   #4
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Quote:
Originally Posted by Braineack View Post
It's the pressure drop through the IC.

When the signal is taken post intercooler, the turbo is free to spool until the pressure reached the signal source. Chances are there is more boost pressure before the IC than after, so if they are running high boost levels there is a chance that it might make a brief boost spike before the pressure reaches the wastegate.

Sourcing the boost at the turbo will slow the response because there is more boost pressure, faster, reaching the wastegate to control/slow the spool.
You mean that the pressure drop is the spiking?

FWIW they only boost to 9psi. But damn they have a 2554R in that car with a 2L engine. I did not test their car but the spool must be funny.
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