MBC stand alone and parallel with a flick of a switch

[syxxty]

First I need to credit this concept from the forum post:

http://www.audizine.com/forum/showth...hlight=mbc+n75

I saw the MBC offered from JHM to adjust boost from inside the car and placed my order. I have a completely stock 2001.5 S4 with a GIAC X ECM. You may say its crazy to install an MBC with K03s because of the following reasons:

- Need a TCD (Throttle cut defender) so the rapid boost build will cause the ECM to cut the throttle
- You will quickly kill K03s
- You need a certain tune to work well with MBC
- etc..

Well I agree. I don't want to kill my sweet little snails. I found the post above and thought this was a great way to actually protect my turbos (plumbing N75 and MBC in parallel), Switching to stock for emissions testing, and going all out with MBC stand alone when I go Stage 3 or go to the track with my Giac X tune (hopefully it wont cut my throttle). The one difference (and purpose of this post) is to replace the manual valves with solenoids to switch back and forth inside the cab.

The pictures below show my pair of solenoids mounted to my sweet custom bracket (thanks lowes). The solenoids are Normally open so there is no way to screw up my turbos if a solenoid fails. I then will wire these to a on/off/on rocker switch in the cab (to accessory power). I plan to do the install this weekend so will let you know how it goes. The hardest part was sourcing the solenoids for cheap. Here is a total of the project:

- (2) STC Air Solenoids (PN 2V035-1/8) - $25
- (1) single pole double throw on/off/on rocker switch - $3
- Brass air fittings (2 plugs, 2 1/8" NPT barbs, and 2 10-32 UNF barbs - $10
- metal angle steel - $4
- Hardware to mount bracket - $3
- JHM in cab MBC - $165
-------------------------------
Total = $210

All in all not too bad. The worst part is that you have to order packages of 10 for some of the brass fittings from McMasterCarr. I just couldn't quickly find any cheaper. My only concern is drilling in to the battery when I mount it and adding too much volume to the boost lines causing a delay in Waste gate response. Let me know if you have any questions or ideas.

Solenoids and bracket:


Bottom:


Stolen concept:

[AudiA4_20T]

so your basically making your own EBC? why not buy a used Greddy one for the same price?

[syxxty]

I may not understand what you are asking but I think the answer is no. This will give me 3 options:

1) Stock - Close the MBC solenoid which is using the stock N75 valve (which is EBC)
2) Parallel (to clip boost spikes) - Leave both solenoids open (supplying no power to either)
3) MBC - Close the N75 solenoid

Best of all three worlds and switch back and forth on the fly inside the car.

[syxxty]

Someone asked me a good question on Audiforums. Do you think boost will leak past the N75 when running the MBC in stand alone? I thought it would go through the N75 and stop at the closed solenoid valve but i forgot about the other connection. I am planning on installing and testing it using just MBC and see if the boost creeps up and would indicate the N75 is leaking the boost. Any help would be much appreciated. TIA.

[JDM EJ1 95]

you can do the same thing with a dual boost controller for cheaper

[syxxty]

I got em installed. Here are the logs from VAG-COM. Apparantly my MBC does not go low enough. I want 15-17 psi but still getting 21 psi peak with the MBC turned all the way down. I can at least see some difference.



planning on putting a softer spring in the MBC.

[rouellettea4]

I got em installed. Here are the logs from VAG-COM. Apparantly my MBC does not go low enough. I want 15-17 psi but still getting 21 psi peak with the MBC turned all the way down. I can at least see some difference.



planning on putting a softer spring in the MBC.

You could potentially have the MBC in backwards, you tried switching the lines from the turbo housing and the wastegate line? I know it could be a silly mistake but I've seen the oversight before. Good work though, impressive setup.

[raketeS4]

nice concept

[o3spec]

dumb idea, more stuff to leak. just do a greddy ebc or parallel a mbc.

[AudiA4_20T]

why would you need to have all the options?

[o3spec]

^^ exactly. mbc is perfectly safe and runs well with everything plus you get so much quicker spooling. it just takes a bit of playing with

[syxxty]

I was worried with all the posts that said I needed a TCD. Plus I thought parallel was the safest so I wanted to be able to switch back if the throttle got cut. If I switch back to my stock tune I can still run the N75 if needed.

[syxxty]

The schematic above is INCORRECT and does not work. Infact any parallel configuration will not work. The pressure the MBC passes will feed back through the T and bleed through the other side of the N75 (and vise-versa). I ended up plumbing my 2 air solenoids on either side of the N75 so now I can only go MBC stand alone or parallel that does not work. Ha.. I thought maybe check valves would work but then how would the pressure on the WG side ever be blead off so you can ask for more boost? I am confused.

Does anyone have a parallel boost control setup that works? If so HOW?

[Caddy7]

Try putting the valves on the wastgate side!

[BlackS4TT(Josh)]

The MBC needs a bleed hole to release boost pressure for MBC-only operation. The MBC needs to NOT have a bleed hole for MBC-N75-parallel operation. I don't think you can put a solenoid on the bleed hole ;) So you'd need two MBC's for this to work.

[orttauq]

Why would a MBC need to NOT have a bleed hole when run parallel to the N75?