Below you see 3 boost curves. First we start with just a hypothetical chip. The next two show two different ways of adding an MBC to the system and how they affect this chip's boost curve.

The N75 Only shows a hypothetical boost curve with a chip and your standard N75 valve in place.

The N75 & MBC in Parallel shows the MBC set at ~17psi, such that any boost above that will get bled off by the MBC, but the N75 will still control the boost curve below the MBC's set limit.
- Here the MBC functions to remove spikes.
- In this configuration, the MBC is only capable of reducing boost lower than what would occur without it.

The MBC Only shows the MBC set at ~17psi, such that the MBC has complete control over the boost.
- Here the MBC functions to control the boost.
- In this configuration, the MBC has full control, and can either raise or lower boost, and thus caution is suggested when doing this. One should have knowledge of fueling limitations, turbo capabilities, etc.




Here's Matt's drawing of the N75 & MBC in Parallel:



PS - It should be noted that with the MBC in place (Only. Parallel too?), the initial ramp of boost may occur quicker as well.

PPS - Having a MBC Only set-up, if you set the boost to a value greater than the turbo can physically achieve, the resulting curve will merely be the max boost (for the given RPM range) that the turbo can sustain. An example of this is that the S4's K03's can not sustain the 17psi at high RPMs as illustrated above. In this case, once the turbos can no longer sustain the 17psi, the boost curve would begin to taper and follow the maximum achievable boost.

Mark P


Dyno: 469wHP / 451wTQ
93 oct - best 60':1.734 | best 1/4ET:12.239 | best 1/4mph:116.58
100+oct - best 60':1.698 | best 1/4ET:11.762 | best 1/4mph:121.72



ECUx template version 11.16 (3/12/07)
AWD Dynos by State - Race Gas in New England - B5S4 100k+ mile post

Current:
'02 Audi S4 Avant, Imola Yellow, APR Stg3 - imolavant website - 180k miles
'01.5 VW Golf 4dr 1.8T, Satin Silver, GT28R, EPL-tuned - 14.8 | 101mph - 192k miles
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'00 Audi A4 1.8T, Silver - Quattrobonium website