Q:  What is boost creep?  Why can't I use a boost controller to control boost creep or lower boost?

In a perfect world, the wastegate should always control the amount of boost the turbo can produce.  No matter what the set-up is, when the wastegate is set for 10psi, it should give you 10psi.  In reality, when the turbine section is overrun, boost creep rears it's ugly head.

Please use a good, aftermarket boost gauge to monitor boost pressures; the stock boost gauge is not accurate enough.

Boost creep is defined as the uncontrollable increase of boost levels.  A boost "spike" is something else that is usually caused by a malfunction of some sort.  Boost creep is due to too much exhaust gas flow through the turbine section.  The stock (FC3S) wastegate is designed to work under stock parameters - stock intake, stock exhaust, stock engine, etc.  Once you start to change or upgrade those components, engine efficiency will increase, and thus, engine exhaust gases will increase.  Upgrading to a freer flowing exhaust will almost always increase boost levels.  Couple this with the small Zenki single-port wastegate, and this is a sure recipe for boost creep. 

Now, let us step back a moment to explain why boost levels increase when you upgrade to a freer flowing exhaust system.  As mentioned previously, the stock wastegate was designed to work with stock components.  Once these components are upgraded to increase engine efficiency, more exhaust gases are produced.  The upgrade, freer flowing exhaust system works on the back end of things by allowing the exhaust gases to exit the engine more efficiently.  By allowing the exhaust gases to exit the engine faster, this causes the exhaust gases to run through the turbine section faster, thus, boost levels rise.  The wastegate is a purely mechanical device; it does not know how much boost the turbo is producing, but boost is controlled relative to the spring pressure inside the wastegate actuator.  Due to the increase in exhaust gas flow from the freer flowing exhaust system, the normally allowable ~6psi of spring pressure is easily overrun, and a higher boost pressure is allowed - the stock 6psi of boost no ends up being 10psi...12psi!

So now we end up with more boost - what do we do about it?  If the boost is under control, why not enjoy the added performance?  As long as you have enough fuel for the higher boost levels, you should be fine.  If you own a Zenki FC3S turbo, boost creep is possible with just an aftermarket exhaust system!  Porting the wastegate can help in most cases.  Listed below are links to wastegate porting for both the Zenki and Kouki turbo's.
FC3S Pro:  How-To - Zenki Wastegate Porting
FC3S Pro:  How-To - Kouki Wastegate Porting

Okay, so how does this all tie in with a boost controller?  Some people assume that a boost controller can lower boost levels as much as it can raise them.  This is wrong; a boost controller cannot lower boost levels from "stock"; if the turbo already makes 12psi with a boost controller, installing a boost controller cannot lower it from the base 12psi.  Why is this?  We need to look at how the wastegate works to understand why...  The wastegate works by pressure.  Once the turbo starts to make boost, the boost needs to overcome the wastegate internal spring to open the wastegate.  Once the wastegate spring is overcome, the wastegate starts to open.  Now, if you want to raise boost, all you need to do is delay the wastegate from opening.  This is easily done by restricting boost pressure going to the wastegate actuator or bleeding the boost pressure to trick the wastegate into thinking the turbo is making less boost than it really is.  By bleeding off boost pressure, this delays the wastegate actuator from opening the wastegate itself, and viola, you get more boost.  So how do you get the turbo to produce less boost?  We somehow need to miraculously open the wastegate earlier!  To do this, we need to pressurize the wastegate actuator earlier / faster than the actual boost from the turbo - this becomes impossible unless you have some kind of pressurize system to do this or a mechanical actuator!  Now you understand why a boost controller cannot lower boost levels from "stock"...

If all else fails, how do you control boost?  Sadly, you need to restrict the amount of airflow going into the engine or restrict the amount of exhaust gases exiting the engine.  Using a smaller air filter can be an opton, especially if you're using cone filters.  Installing a restrictor plate in the exhaust system can control boost creep; we've used a 2" opening cut into some sheetmetal then installed between the downpipe and pre-silencer to drop boost from an uncontrolled 13psi to 14psi down to a managable 10psi.  By drilling two holes for the bolts and lining them up with the flanges, this is an quick and easy fix if need be.

Questions?  Comments?  Send email to:  reted(at)fc3spro.com