Your MBC, is it a hardware store built piece? If so, does it have the little hole drilled in it? I recently installed a home built MBC and followed the instruction, drilling the little pressure relief hole...and the hole renders the MBC useless. All the boost pressure that would be transferred to the waste gate actuator just leaks out the hole.

Drop Top Road Trip said:

Your MBC, is it a hardware store built piece? If so, does it have the little hole drilled in it? I recently installed a home built MBC and followed the instruction, drilling the little pressure relief hole...and the hole renders the MBC useless. All the boost pressure that would be transferred to the waste gate actuator just leaks out the hole.

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Nope. Hallman pro boost controller. It does have the vent hole but that's part of the design straight from hallman

I can't understand how a boost controller with a built in leak can work. Logic says it just can't, but maybe someone with some engineering experience can explain it. Mine had me spiking to more than 20psi under any and all adjustments (pegging my boost gauge) so I removed it immediately.

I bought it used from a friend but it worked when it was on his. My guess is the MBC itself or the wastegate stuck but I'm open to other opinions. Also hoping someone can answer my safc question. It seems crazy to be taking out 37% on 550s and still run rich

Your understanding isnt far off. When you build up pressure the excess pressure needs to leak. How else could you hold steady pressure? If there was no leak, you would spike to as much pressure as the turbo could make (or system could take) until something let go.

I would uninstall your mbc and open it up all the way. Blow into the mbc from the bottom side, where the boost would go in to. If you can feel air coming out the other side, more then likely it is working. I would still open it up to inspect the internals. Worst case, remove it from the system and see if the problem still occurs. If it does its the wastegate or flapper. Normally when you get boost spiking it is in reference to the wastegate not opening. Be it stuck, or a mbc limiting the usage or range of motion. Double check that to be sure. Hope this helps a little.

livedsm4g63 said:

Your understanding isnt far off. When you build up pressure the excess pressure needs to leak. How else could you hold steady pressure? If there was no leak, you would spike to as much pressure as the turbo could make (or system could take) until something let go.

I would uninstall your mbc and open it up all the way. Blow into the mbc from the bottom side, where the boost would go in to. If you can feel air coming out the other side, more then likely it is working. I would still open it up to inspect the internals. Worst case, remove it from the system and see if the problem still occurs. If it does its the wastegate or flapper. Normally when you get boost spiking it is in reference to the wastegate not opening. Be it stuck, or a mbc limiting the usage or range of motion. Double check that to be sure. Hope this helps a little.

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Could my bov set screw need adjusted? If the bov is letting it go it would hold high boost right? I had the problem after I installed the bov and mbc. Whenever I'm in boost and let off I get super loud turbo flutter sounds

This would cause a surging issue. The bov doesnt limit the amount of boost you see. It releases the pressure you've already placed into the system. Sounds like there may be multiple issues.

a good friend who knows all about these set the bov set screw for me so I would assume it's fine. I just can't figure out why it's overboosting. It's either stock wastegate 13psi with no mbc or I put the mbc on and I'm stuck open at 26

jdm9221 said:

a good friend who knows all about these set the bov set screw for me so I would assume it's fine. I just can't figure out why it's overboosting. It's either stock wastegate 13psi with no mbc or I put the mbc on and I'm stuck open at 26

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Well if your stock wastegate is working as intended (13psi) and the wastegate is not allowing you to limit the boost, this would point to either a blockage in the vacuum lines or a defective mbc.

I just ran all new vacuum lines when I put the vacuum line nipple in for the j pipe yesterday

The fitting with the vent hole on the right port?

Lets go back to your original post...

jdm9221 said:

...Before I was only hitting 13psi because it was leaking from my bov, replaced that(recirculated to the intake) and now it's hitting 26psi with the boost controller turned all the way down.

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You answered your own question in your post, before you were hitting 13psi because you had a leak at your bov. The leak at your bov was, in a round about way, acting as a boost controller which is why you were able to maintain 13psi so the instant you replaced it your system relies on the wastegate to control boost, i.e., the amount of exhaust gas that flows over the turbine to increase/decrease the amount of pressure the turbo will spool to.


My recommendation is to check if you're experiencing boost creep by removing the wastegate actuator (wga) arm from the flapper on the hotside of the turbo. Just pull the grenade pin and slide the arm off of it then go for a drive, if it builds 13psi without the wga installed its boost creep. To reinstall you'll have to pull straight out on the wga arm (it's under tension) and extend it out to the flapper. On a properly functioning turbo exhaust waste setup you should build 0psi even at WOT with the wga removed.


If you're suffering from boost creep the only way to fix it is...
Here's a good image the JusMX posted about porting the hotside if you go that route.



While you're in there it doesn't hurt to port the o2 housing wastegate port outlet either which helps the exhaust transition back into the stream without creating turbulence or high pressure there.

91talonts1 said:

The fitting with the vent hole on the right port?

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Goes from the wastegate to the vented hole side, other side to my j pipe

I've never had boost creep. I also installed the boost controller and bov at the same time. I'm going to take out the boost controller and see what it hits rn

Did you even read gofer's post? maybe you didn't have boost creep because the turbo couldn't keep up with the massive boost leak generated by the BOV.

Can you tell us if your 16g has been ported? What exhaust are you using?

It's a non port 16 and a thermal exhaust. Even at 26 there's no boost creep

You're not understanding the concept of boost creep, bud.

If you're hitting 26psi and trying to run wastegate pressure at 13psi then it's creeping 13psi, whether that's because you're wastegate isn't efficient enough or it's because of a faulty boost controller that's what you're going to have to troubleshoot.

gofer said:

You're not understanding the concept of boost creep, bud.

If you're hitting 26psi and trying to run wastegate pressure at 13psi then it's creeping 13psi, whether that's because you're wastegate isn't efficient enough or it's because of a faulty boost controller that's what you're going to have to troubleshoot.

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I'm not trying to run wastegate pressure tho, That's why I bought the mbc. I'm trying to set it to 19 pounds. If I run a straight line from j pipe to wastegate it obviously runs 13psi. If I throw the mbc between it then I can't change it other than 26. If my wastegate was the problem it would overboost without the boost controller in the equation

jdm9221 said:

...now it's hitting 26psi with the boost controller turned all the way down.

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jdm9221 said:

I'm not trying to run wastegate pressure tho

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If your boost controller is turned all the way down then you're trying to run wastegate pressure...

Literally an hour ago (post #15) you said you were going to pull the mbc and see what happened, then never came in and updated the thread with your result.

I said it wasn't wastegate pressure because I thought the boost controller was at fault I took the boost controller out of the equation and it's still at 26 so now how do I go about fixing my wastegate

Check to see if the waste gate flapper move freely with wga arm removed. (Could be a stuck flapper) Next check the actuator itself by pumping compressed air (13~15psi)through vacuum line to the actuator.The arm should move at 13 psi if the spring rate is 13 psi. Check for leaks if the valve/arm doesn't move. If both are in working order, it could be creep like gofer stated.

Read the entire post I made above, it tells you how to troubleshoot it in detail by just pulling the cotter pin off the wga flapper, pulling the wga arm off, then going for a drive.

Wg pressure also is probably not 13. A stock actuator is like 9psi all by itself.

You don't mention any exhaust mods in your profile, so I doubt it's boost creep. 16gs are notorious for creep on a 3" catless exhaust, the usual fix being porting as gofer mentioned and/or a tubular O2 housing (02 dumps rarely help). I'm betting on the WG.
You definitely have something going on with your safc as 550s in a 2g should require very little adjustment. Make sure you don't have any boost leaks as they will make you run rich. You may want to invest in a afpr as some people have problems with a 255 over running the stock fpr.
http://www.roadraceengineering.com/newafc.htm