05/09/05 12:50 PM
Need schooling on MBC + boost gauge

Alright guys, I feel like such an ass for posting in the newbies forum, but I didnt think this belonged anywhere else.

I hooked up my MBC like I do in every other DSM I have ever owned, from the nipple off of the turbo "J" pipe to the input side of the MBC, then the output vaccuum line from the MBC to the wastegate.

It works awesome, and this is how I have been doing it for years. However, I just picked up the AMS kit (until my profec B can be bought) and the directions have the boost source coming from the BOV line to the intake manifold. (Where my boost gauge is tapped).

Now, here is the question, am I loosing out on anything by hooking it up the direct route like I did above instead of the BOV route. The reason I am asking is that line creates vaccuum, so does the MBC need that vaccuum to open and close the wastegate with more precision?

Obviously if I only hook it up to a nipple off of the turbo then there will never be a vaccuum source. My boost hits 15 psi faster than a raped ape, but tapers off to about 11-12 psi by 6k or so. Would hooking it up through the BOV line remedy this problem and keep me at a solid 15psi? I dont think it would, and I havent checked for boost leaks yet, which would definately contribute to the loss of boost at higher rpms...

Just thought I would ask to see everyones opinion, im guessing a boost source is a boost source, nuff said. The reason I have always hooked it up to that little nipple is because that is the fastest possible way to get a boost source (right off the compressor) which would hopefully actuate the mbc and wastegate faster and with more precision...I think so anyways.

Would the mighty car gods that invented ball bearing turbo's and titanium retainers please chime in...

(Dr. Pilosh Haagenscodyberger)
05/09/05 01:40 PM
Re: Need schooling on MBC + boost gauge

I have always tapped into the BOV line. Thats how all the Vfaq's I have read said to do it. So I did it that way. I suppose one might be better for a specific reason but I couldn't tell you what it is.

Well a quick search found this article on the net. I don't know how accurate it is though, maybe someone can clarify.


"This is a quick overview of the correct way to install a manual boost controller on your turbo DSM.

First, the stock boost control system: There is a pressure source on the turbo outlet elbow (1g) or the compressor housing (2g). That pressure source goes towards the wastegate actuator, but first it has a tee in it. That T splits the source between the WGA and the BCS (boost control solenoid).

The WGA works by opening the wastegate up when it recieves a pressure signal. In order for the car (stock) to increase the boost, it uses the BCS to bleed some of the pressure in the source line off. thus decreasing the pressure that the WGA sees.

When you install a manual boost controller, you are simply replacing this system with a preloaded, pressure-activated valve. That way, the WGA won't see any pressure, until the boost goes about the preload set into the MBC.

First, remove the stock system. Unplug the BCS (or leave it plugged in and toss it aside), remove all the hoses, and cap off both the original source and the fitting before the turbo that the BCS went back to. You won't be needing any of these.

Now, install the new MBC. First, you need to pick a source. Your source has to be a decently sized pressure port AFTER the throttle body. That means that you can not use the throttle body ports (too small) and you can't use anything on the intercooler pipes. Most people tee into the BOV line, and some run a seperate source from the PCV nipple, or their own extra nipple.

You HAVE to use the intake manifold is you want proper boost control. Why is that? The manual boost controller regulates the amount the wastegate is open based on the pressure at its source. Since you want to control manifold pressure, you want the MBC and the WGA to be recieving pressure directly from there.

Using a source off the turbo or intercooler pipe can cause you to have boost that changes with weather, load, and engine speed, and can also slow down boost response. By comparison, a manifold source will be fairly steady, solid, and reliable.

Then connect the source line to the "in" side of the MBC. On most boost controllers, this is the bottom; it will always be the side opposite the adjustment screw (for ball-and-spring MBC's, which are the only kind worth running).

Then, connect the "out" port on the MBC to the wastegate actuator.

Try to minimize the length of all the hoses, and make sure to zip tie them securely such that there are no leaks. Use hose that fits over the fittings well, don't go too big or too small.

All MBC's will have some kind of vent hole after the spring; most new ones have this drilled into the body of the MBC, but some older ones have a seperate piece which goes in the out line. Make sure this is intact and uncovered.

Mount the MBC securely, and go for a test drive! Start with the boost tuned all the way down (generally counter-clockwise) and slowly bring it up to where you want."

05/09/05 02:06 PM
Re: Need schooling on MBC + boost gauge

That was really helpful!

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