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Re: 9000 MBC+A
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Posted by Jeff in ATL (more from Jeff in ATL) on Thu, 12 May 2005 12:54:13 Share Post by Email
In Reply to: Re: 9000 MBC+A, Dexter J, Thu, 12 May 2005 11:57:14
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Hey Dexter,
Let me first clear up the MTB and what I said.
What I meant to say is that the MTB poses a problem with finding a good pressure source to tap for boost at the TB. The older mechanical TB has the IAC valve which can work well for a pressure tap.

As for a Ball and spring design of a MBC...There are good points and bad points. The good points are that the turbo spools up faster than a baisc bleed valve that is applying pressure on the WGA all the time and eventually cracks open progressively. The reality of a Ball and spring MBC is that it doesn;t just lift off as one would think. It cracks open but the progression has a high curve. Opens slightly later which allows more time for a turbo to get going thus reducing lag. So it has a tendency of overshooting more than a bleed style MBC. The +A is designed to apply pressure on the WG. One could use it creatively to apply pressure to smooth the curve and act much more like stock BPC. That is definitely an option. Most don't like this due to the turbo response slower or more "stock like.', But that sounds like what you are after.

A word on Ball and spring MBC's....I have used one for just under two years...it is as clean as the day I put it in internally. But I suppose that might show the condition of your car if it isn't clean. I guess stock BPC';s go bad or get dirty and malfunction as well. Right?

Bleed valves, whcih you expressed interest in would be an option, but most find out that they have their own probelms...slow turbo response, still overshoot. Why? Because of flow problems. A bleed valve restricts the pressure flowing theouh the device. It set too high, there will never be enough pressure to crack open the WGA. If set too low, nothing is achieved by using it.

The MBC+A was born out of the desire to run as close to the fuel cut as possible without overshooting and a device that doesn't have to be adjusted when the temperatures drop and the colder denser air brings turbo on real fast and furious. So a solution for the constant adjustment of the MBC. MBC+A is closer to set and forget than the MBC alone is.

There is another option which might interest you: A diaphragm style pressure relief valve. This has a smoother release than a Ball and spring MBC. Turbo spool will be slower than a Ball and spring MBC but it will release to its flow capacity once the achieve psi is reached. This is something a bleed valve cannot do. A restrictor continues to restrict, a pressure relief valve opens and allows full flow.

I have two MBC+A kits going out in the next couple of days for some independent testing. Maybe I will have more feedback and observations after that, but I bet it would work for you. Either that or the diaphragm pressure relief valve.





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