# MBC Inline With N75



## Raek (Aug 1, 2003)

Hey guys, 

I tried searching in this forum, and didn't really venture out yet. So, I figured I'd open some dialogue 

As some of you may know, I went with Frankenturbo towards the end of 2014, and while it's generally been awesome...an engine with 132k has it's issues.

It's been pretty solid for the most part, but I went through some overboost issues that were clearly from my OG N75 valve. Funny, because coming from a chipped MKIV, I should've kept that prominent in the diagnosis, but silly me thought it was a ECU management issue. 

That particular overboost issue kept popping off my OEM turbo outlet hose, which was pretty oil soaked and flimsy after driving a few thousand miles on a leaky original turbo. So, I replaced it with a Forge turbo outlet. That also kept blowing off until I figured out the N75 problem.

Anyway...after driving the car more frequently (I had it stored during the most gnarly part of the winter, shortly after getting everything in check), it happened again. I'm pretty certain that I didn't blow through another N75 and that the hose was just kind of working it's way off since the Forge hose is somewhat shorter than OEM. 

But, just for added safety, I picked up an Integrated Engineering MBC. I've read that a solid MBC setup inline with the stock boost control can help with problems in spiking, etc...but, then I've also read that they can blow up your engine and ruin your life (go internet).

Is it worth it to install it? Also, I've searched for a couple of DIYs, but does anyone have any experience currently?

TIA


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## Tempes_TT (Oct 24, 2010)

I personally haven't done it myself, but what I have read, is that a lot of people keep the n75 electrically plugged in, but the plumbing completely unplugged, so the n75 is just... There. 

This of course is with a manual boost controller in its place :thumbup:


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## l88m22vette (Mar 2, 2006)

Good write-up: http://www.audiworld.com/forums/s4-...s-mbc-vs-both-affect-boost-i-drew-up-1526679/


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## 225TTed (Nov 28, 2014)

I have one plumbed in to stop my boost spikes. Works amazing. I used to spike 27psi and hold 17-18...  but now I consistently spike 20psi and hold 17/18. 

I've never heard of them failing and lunching the car. I think if mine failed, it'd just do its normal business or just bypass the n75 and run the whopping 7psi off the wastegate.


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## Raek (Aug 1, 2003)

l88m22vette said:


> Good write-up: http://www.audiworld.com/forums/s4-...s-mbc-vs-both-affect-boost-i-drew-up-1526679/


Sweet!




225TTed said:


> I have one plumbed in to stop my boost spikes. Works amazing. I used to spike 27psi and hold 17-18... but now I consistently spike 20psi and hold 17/18.
> 
> I've never heard of them failing and lunching the car. I think if mine failed, it'd just do its normal business or just bypass the n75 and run the whopping 7psi off the wastegate.


And, sweeter!



Also, before I replaced my crapped out N75 I was boosting at 25psi+ (my boost gauge only goes to 25). At that point, it would blow the turbo outlet off (which is a good thing...only happened twice, and I don't think any damage occurred due to the point at which it would come loose).


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## 225TTed (Nov 28, 2014)

Raek said:


> Sweet!
> 
> 
> 
> ...


When I was spiking 27psi, I noticed the clutch started to slip a few hundred rpm (no smell, only on 6th gear punches on the highway... Like passing someone without downshifting). After toning the spike down, it went away. I know I need to do the clutch/dmf, but this helps prolong the inevitable.


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## D2O (May 12, 2012)

I run both as well for my Frankenturbo. Make sure it is plumbed in PARALLEL and not in series (aka inline) - otherwise you have the worst of both worlds.


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## l88m22vette (Mar 2, 2006)

A trick setup could be psi switch to "eliminate" the N75 in higher boost, you'd get more refined OEM boost behavior with your own boost limit. You cannot disconnect the N75 because it would immediately throw a code, but you could use a Hobbs boost switch and a solenoid to shut off the connection to the wastegate. So,

intake man--(hose)---tee------------------MBC--------------|
|--------------N75------solenoid----tee------------wastegate

Does that make sense?


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## jsmith2015 (Mar 7, 2015)

l88m22vette said:


> A trick setup could be psi switch to "eliminate" the N75 in higher boost, you'd get more refined OEM boost behavior with your own boost limit. You cannot disconnect the N75 because it would immediately throw a code, but you could use a Hobbs boost switch and a solenoid to shut off the connection to the wastegate. So,
> 
> intake man--(hose)---tee------------------MBC--------------|
> |--------------N75------solenoid----tee------------wastegate
> ...


That is a very interesting idea. Any ideas on a suitable solenoid ?


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