Installed TST PM3 to play along with my Smarty!!
06-10-2006, 11:58 PM
#16
Registered User
I don’t think he's experiencing surging. He's getting a boost spike, which is typical. If he were to drill the divider it would take care of the problem somewhat. Porting also helps. You have to have a boost control of some type. If you didn't the boost pressure along with drive pressure would be through the roof. <-- on his setup.
06-11-2006, 07:20 PM
#17
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RJ--
I installed a JoeP MBC a couple weeks ago.
You are sort of correct on the operation, but you're not accounting for the ball-and-spring function.
There is a spring-loaded check ball inside most MBCs. The boost signal must overcome this spring tension and unseat the ball in order for the WG to see a boost signal. When you adjust your MBC, you are adjusting the preload on this spring.
Now, if it takes 32psi to unseat this spring, then the WG won't open until 32psi of boost. This represents about 11psi above the mechanical WG setting (rod length adjustment). RJ is correct in that the MBC can only RAISE the point of WG opening. It cannot lower it below the mechanical setting.
But it WILL "regulate" boost in the sense that it will hold boost to a certain limit. You can see how the ball-and spring design prevents a mode of operation that is widely believed but mistaken-- namely, that the MBC will raise the psi at which the WG will open, but once the WG is open, it will "blow down" all the way to the mechanical WG setting. Instead, what actually happens is that the boost will "blow down" to the setting of the MBC, not the mechanical wg setting.
This is because the spring is linear in operation. Namely, if it takes 32psi to open it, it will be closed below that boost pressure, whether boost is rising or falling.
Now, some MBCs use a gated design that allows the opening and closing points of the WG to be different. You will often find that setting it to open at 37psi will cause it to blow down to 31psi. This is because there's a "gating" function that will delay the WG opening to a point higher than it would otherwise be.
JH
I installed a JoeP MBC a couple weeks ago.
You are sort of correct on the operation, but you're not accounting for the ball-and-spring function.
There is a spring-loaded check ball inside most MBCs. The boost signal must overcome this spring tension and unseat the ball in order for the WG to see a boost signal. When you adjust your MBC, you are adjusting the preload on this spring.
Now, if it takes 32psi to unseat this spring, then the WG won't open until 32psi of boost. This represents about 11psi above the mechanical WG setting (rod length adjustment). RJ is correct in that the MBC can only RAISE the point of WG opening. It cannot lower it below the mechanical setting.
But it WILL "regulate" boost in the sense that it will hold boost to a certain limit. You can see how the ball-and spring design prevents a mode of operation that is widely believed but mistaken-- namely, that the MBC will raise the psi at which the WG will open, but once the WG is open, it will "blow down" all the way to the mechanical WG setting. Instead, what actually happens is that the boost will "blow down" to the setting of the MBC, not the mechanical wg setting.
This is because the spring is linear in operation. Namely, if it takes 32psi to open it, it will be closed below that boost pressure, whether boost is rising or falling.
Now, some MBCs use a gated design that allows the opening and closing points of the WG to be different. You will often find that setting it to open at 37psi will cause it to blow down to 31psi. This is because there's a "gating" function that will delay the WG opening to a point higher than it would otherwise be.
JH
That's how I thought it worked!!
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