Cincy
01-28-2009, 09:27 PM
Since there is so many questions and misinformation that keeps getting posted about mbc's on the forums, i thought it would be nice to have actual information posted that people can refer to and get all their questions answered.
To start, there is 2 main types of mbc's, the bleed valve and the ball/spring.
BALL/SPRING.
http://i30.photobucket.com/albums/c310/SkyeMaloney/step61.jpg
As you can see in the pic, it is a VERY simple device and can be made with simple parts found at the home improvement store.
SO HOW DOES IT WORK? The boost pressure comes into the mbc from the bottom where the ball is set to restrict the flow to the wastegate. The spring tension set by both the spring and the knob will determine how much force (psi) it takes to push the ball up high enough for the pressure to reach the wastegate and then open the flapper/valve to bleed off excess exhaust gas to regulate the psi.
http://i44.photobucket.com/albums/f5/brute_nm/mbc1-1.jpg
By changing springs with different spring tension, you can change the amount of psi the mbc can hold and allow the turbo to run. For example, a softer spring can go 5-25psi and a stiffer spring will go 15-35psi (just an example).
The ball inside can also make a difference. A stainless ball that comes standard in most mbc works well and reacts slower than a ceramic ball that is an optional upgrade on some mbc's. This helps decrease lag.
BENIFITS AND WHAT IS IT GOOD FOR? This type of mbc is a great for larger turbos that have some actual lag. The reason being the wastegate sees no pressure and remains closed until the psi set from the mbc is reached resulting in a decrease in lag by a couple hundred rpms and also slower psi drop off in higher rpms. NOT GREAT ON STOCK TURBOS
BLEED/GATED VALVE
http://www.boostvalve.com/images/bleedflow.jpg
HOW DOES IT WORK?As you can see in this pic, the bleed doesnt ever fully close and constantly bleeds off psi. You restict the airflow, the psi increases and increase the flow, the psi drops. This allows some pressure to reach the wastegate allowing it to open a small amount to help regulate psi.
BENIFITS AND WHAT IS IT GOOD FOR? Since the mbc constantly bleeds off psi and allows some pressure to reach the wastegate, it helps smooth out the boost onset and smoother boost. This type of mbc is HIGHLY recommend for a small turbo like those found stock in our cars. These result in a lot less of the common "on/off" feeling that mainly claim with the ball/spring mbc.
COMBO MBC
You can find some mbc's that have both a bleed and ball/spring together. The most common one is the turboxs hpbc. This is a great mbc type that can adjust psi all the way up to 30psi over wastegate pressure and still manage to smooth out boost for a small turbo and hold psi longer. Deff worth the investment since it works well with both small and large turbos.
WHAT ABOUT DIFFERENT N75's
The one true drawback of a n75 is that you cant decide what psi you wish to run or that it will work with your chip tune. Not to mention they cost just as much as most major mbc brands and dont hold psi any better than the stock version.
To start, there is 2 main types of mbc's, the bleed valve and the ball/spring.
BALL/SPRING.
http://i30.photobucket.com/albums/c310/SkyeMaloney/step61.jpg
As you can see in the pic, it is a VERY simple device and can be made with simple parts found at the home improvement store.
SO HOW DOES IT WORK? The boost pressure comes into the mbc from the bottom where the ball is set to restrict the flow to the wastegate. The spring tension set by both the spring and the knob will determine how much force (psi) it takes to push the ball up high enough for the pressure to reach the wastegate and then open the flapper/valve to bleed off excess exhaust gas to regulate the psi.
http://i44.photobucket.com/albums/f5/brute_nm/mbc1-1.jpg
By changing springs with different spring tension, you can change the amount of psi the mbc can hold and allow the turbo to run. For example, a softer spring can go 5-25psi and a stiffer spring will go 15-35psi (just an example).
The ball inside can also make a difference. A stainless ball that comes standard in most mbc works well and reacts slower than a ceramic ball that is an optional upgrade on some mbc's. This helps decrease lag.
BENIFITS AND WHAT IS IT GOOD FOR? This type of mbc is a great for larger turbos that have some actual lag. The reason being the wastegate sees no pressure and remains closed until the psi set from the mbc is reached resulting in a decrease in lag by a couple hundred rpms and also slower psi drop off in higher rpms. NOT GREAT ON STOCK TURBOS
BLEED/GATED VALVE
http://www.boostvalve.com/images/bleedflow.jpg
HOW DOES IT WORK?As you can see in this pic, the bleed doesnt ever fully close and constantly bleeds off psi. You restict the airflow, the psi increases and increase the flow, the psi drops. This allows some pressure to reach the wastegate allowing it to open a small amount to help regulate psi.
BENIFITS AND WHAT IS IT GOOD FOR? Since the mbc constantly bleeds off psi and allows some pressure to reach the wastegate, it helps smooth out the boost onset and smoother boost. This type of mbc is HIGHLY recommend for a small turbo like those found stock in our cars. These result in a lot less of the common "on/off" feeling that mainly claim with the ball/spring mbc.
COMBO MBC
You can find some mbc's that have both a bleed and ball/spring together. The most common one is the turboxs hpbc. This is a great mbc type that can adjust psi all the way up to 30psi over wastegate pressure and still manage to smooth out boost for a small turbo and hold psi longer. Deff worth the investment since it works well with both small and large turbos.
WHAT ABOUT DIFFERENT N75's
The one true drawback of a n75 is that you cant decide what psi you wish to run or that it will work with your chip tune. Not to mention they cost just as much as most major mbc brands and dont hold psi any better than the stock version.