Dual Stage MBC??

[Mk3 TurboS]

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Just a quickie guys, Don't flame me cause this is just a thought. At the moment I have two MBC's. One is a BLITZ incabin MBC with a nice big shiney knob coming out of the cigi lighter hole, while the other is a turbotech MBC (the ones that have been getting rave reveiws). Now heres my thought. Could I set them up in Series, and adjust the second one (the Turbotech MBC under bonnet) to the higer setting, say 12psi (i have the supporting mods BTW) and set the Bitz one (incabin) to 9 psi. Then when I want to run 12psi exactly I could just crank the Blitz one right up, knowing that I will only hit 12psi as thats all the second MBC will let the boost reach, no matter how much I turn up the Blitz one.

Now before you all scream and say whats the point as the Blitz one can just be adjusted, it near impossible when in a hurry to just turn the big shity knob and get exactly 12psi, you might get accidently hit 14. I guess it a nice safety feature and saves you worrying about over boosting when uping a MBC. Anyone done this or have any thoughts?

 

[MKIIINA]

should work fine but why not just get an EBC that you can set before hand? More parts = greater chance of failure.

 

[Mk3 TurboS]

1. The Blitz one came with the car
2. The Turbotech one was $35au (Massive in Aus at the moment)
3. The whole set up will only cost $35 and no wiring involved.

 

[driftingsteveo]

i agree it would work but i would just go with the electronic boost controller...less moving parts .,,,less chance of failure....plus must more dependable,,,,less chance of a spike or a drop like manual controllers

 

[Orion ZyGarian]

I've heard the opposite.

Anyways, Dr. Jonez sells ball and spring MBCs IIRC for $25, or http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7983320098&category=33742 for $15 shipped

 

[Mk3 TurboS]

I'm not saying MBC's are more reliable but I still have not seen a thread titled "having troule with my MBC" or "How do you wire this MBC" or "setting my MBC" LOL

If I could afford an EBC i'd already have one, BUT for $35 its not a bad way to have a 2 stage boost control system that is gauranteed not to over boost (not including spikes, from what ive heard DR Jonez's MBC dont and niether does the Turbotech one I have).

 

[mdr40z]

I ran similar to that for quite some time except I ran a solenoid valve that switched from stock boost to mbc, I suppose you could do the same thing with two mbc valves

 

[soup]

:withstupi

I'll be doing this soon

 

[Mk3 TurboS]

Cool well I was going to do it this arvo but I'll get the Turbo seals done first. Then take some pics and let you all know how it goes. An easy way to set them is to wind the first one up as high as it will go and wind the second one as low as it will go. Set the second one first to the high boost setting then just wind the first right down.

1 1 was a race horse 2 2 was 1 2, 1 1 went and 1 1 so 2 2 1 1 2.

All most as confusing as this post. LOL

 

[MKIIINA]

fuck....i really dont understand now....might be the beer and margaritas and tequila and rummm but ok 11 22 whatever :bigthumb:

 

[soup]

binary gone wrong!

 

[GrimJack]

This will work very nicely, with one exception. When you wind up the second controller to get your high setting, you will lose your 9psi low setting, and have to muck with it again.

Now if you buy a vacuum solenoid and wire a switch into the cabin, you can have it select from one MBC or the other at the flip of the switch.

 

[Mk3 TurboS]

Not neccessarily My lowest boost is about 8-9psi now since I have BPU, Including a Big arse FMIC. So all I have to do is turn it right down. I not to concerned if the low setting changes betwen 6-9, it more of a cruise setting. Thanks for your input however.

 

[encomiast]

Sorry if this is a stupid question.... an MBC works by basically constricting the diameter of the line going from the turbocharger to the wastegate actuator, right? The more constriction, the less pressure to the wastegate actuator, the more boost in the end.
So, to limit the maximum boost, you'd have to limit the maximum constriction in the pressure line....but how could you do that if the two MBCs are hooked up in series? No matter how the under-hood MBC is adjusted, if the in-car MBC is closed all the way, there will be no pressure applied to the wastegate actuator.... what am I missing?

To my understanding, it could only work if you hooked up the MBCs in parallel...can someone please enlighten me?

 

[GrimJack]

There are 2 kinds of MBCs, the bleeder type, and the ball and spring type.

The bleeder type just lets some pressure bleed off to the outside, lowering the pressure that the actuator sees.

The ball and spring type remains closed until a certain pressure is hit, then allows everything beyond that pressure to go by.

Both of them would work fine in series.

 

[encomiast]

Thanks a lot for the explanation

But somehow I still don't quite get it why they would work in series.
Let's say we have two ball-and-spring MBCs in series. One is halfway closed (supposed to limit the maximum boost) and the other one is fully open, so it exerts almost no tension to its spring. This would be the "low boost" setting, right? Now if we want to go to the "high boost" setting, we close the second MBC all the way, thus tensioning its spring. If I'm not mistaken, this is what the OP wants to do with his in-car MBC: either open it all the way or close it all the way.
But now when the turbo starts to spool, the pressure still has to overcome the force of the second MBC's tightly tensioned spring before it can reach the actuator, doesn't it? With the second MBC fully closed, the setting of the first MBC doesn't matter at all because the pressure won't get past the second MBC and on to the actuator anyway, at least not before the pressure has climbed far too much.
So as I see it, two MBCs in a row could only supply for a minimum pressure, but not a maximum pressure.
Where's the fault in my logic...?
Thanks a ton for your patience!

 

[GrimJack]

You know, it's a damn good thing you're here to point out the flaws in my logic.

I'm going to have to change my tune and agree with encomiast on this one folks, he's right. Running two MBCs in series will always get you the higher of the two settings in boost.

 

[Mk3 TurboS]

I think, THINK, you may have my idea backwards. The second MBC would be set to the higher setting, say 12psi. while the first (incabin) would be turned down as low as possible, 6-8psi. So at this stage the car would only run the lower setting, cause thats all its being alowed to run.

Now when you want the high setting, you wind the first MBC (incabing, which is set to the lowest setting) right up. Although it will be letting through stupid amounts of boost, maybe 1.5 bar??, the second will only allow 12psi.

With the second MBC fully closed, the setting of the first MBC doesn't matter at all

 

[encomiast]

Thanks Grim, I was already doubting my mind

Mk3 TurboS,
it's actually working the other way round, you have to think backwards. The order of the MBCs doesn't matter at all.
The maximum boost of the turbocharger is regulated using the wastegate door which is moved using the pressure produced by the turbo itself. The more pressure the turbo produces, the wider the wastegate door will open, thus letting exhaust gasses bypass the turbine wheel and preventing the shaft from increasing speed.
To accomplish this, there is a line going directly from the compressor housing of the turbo to the wastegate actuator. This is the line you are tapping into with an MBC. The MBC raises the effective boost produced by keeping the pressure in this line away from the actuator (ball-and-spring type) or by reducing it (bleeder type). When all the pressure gets through to the actuator, the wastegate will fully open, if none of the pressure gets there, the wastegate stays closed and the boost keeps climbing until either the turbo is "out of breath" or the pressure is high enough to get through the MBC and in turn opening the wastegate door.

That's why you have to think backwards; the more pressure you have in that line, the less boost you will end up with, and vice versa.

However, I think you could limit maximum boost and achieve what you're after by running two MBCs in parallel

 

[GrimJack]

Agreed.

Another way to look at it - analyse all possible combinations.

MBC #1 set to 9 running into MBC #2 set to 12 = 12psi.
MBC #1 set to 30 running into MBC #2 set to 12 = 30psi.

The reason for this is that the MBC won't let *any* pressure by until it's setting is reached.