In general, I would say that people don't need an MBC in parallel unless they find out then need one. That is, I wouldn't put it on an initial shopping list, but rather only look for one if I felt I had some overshoot/spike condition.

That said, because an MBC in parallel is used as a safety type (boost limiting) setup (as opposed to MBC-only which could creates more boost), there's not a downside to having it. The only issues I can think of would be:
- installing it properly
- setting it properly

Assuming it's installed properly (connected to the right hoses, without pinching any of them or causing leaks), then setting it can be done with just a boost gauge. Logging can certainly help, but you can get it pretty well dialed in with just a boost gauge. This somewhat assumes you already know the desired boost curve of the chip you're using, however not completely necessary.

What I would do is find the RPM in a specific gear (3rd or 4th usually works) that causes the highest boost spike when you go from coasting to WOT. I've found this near 4000 RPMs in my current setup. So if I'm at 4000 in say 4th and go WOT, I'll create the highest boost spike, which will then likely cause and undershoot. So imagine (example) I normally see 30psi (this is where it's handy to know what the software is trying to achieve by looking at prior logs), but when I do this test, it gets up to 32psi, and then drops to 27psi right after, before heading back to 30psi and then continuing the normal curve. Now I can slowly change the setting on the MBC to get it so it only overshoots to say 31 psi and doesn't undershoot below 30psi following that. Sometimes it's easiest to make these changes by starting at low psi MBC setting (ie start at 10psi and make 1/4 turns or whatever seems a good increment on your MBC, slowly getting to that desired result). If you start at the high end and work down, it's harder to tell if you're doing anything (ie if it's set up at 40psi, and you're changing it 1psi at a time, you won't see any results for the first 9 test)

Hope that makes sense. Jekyll just pulled in my driveway, so I gotta run ;-)

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

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