n75 valve
#1
08-17-2010, 07:16 PM
n75 valve
well ive been on here the last few nights just reading up, i think i went all the way to page 30 haha, anyway, i decided to replace my n75 with a forge MBC. with the n75, i would peak around 22 psi and run on 19. since i put in the MBC, no matter how "open" i make it, 17 seems to be the limit, but it doesnt peak it just goes right to 17 and stays. i was just wondering if someone could explain to me how exactly the n75/MBC controls the wastegate. i also was wondering why there's even a plug in the intake for the n75/MBC. on the n75 i noticed that the valves going to the WG and to the turbo were always open, while the intake's was variable. on this MBC the intake to the WG is constant while the turbo valve is variable?
#2
08-17-2010, 08:11 PM
I don't see the point in using an mbc in place of the n75, at least with the stock turbo.. and especialy if using a ball and spring style mbc. It's like replacing a dimmer switch with an on/off switch. I think electronic boost regulation is preferable if possible.
This pic shows how the wastegate works
This pic shows how the N75 works
This pic shows how the wastegate works
This pic shows how the N75 works
A "No-Flow State" exists during idle, when there is no boost and the Waste Gate is held shut by the spring in its actuator (Pressure Unit).
When you step on the accelerator, boost builds up, and so does the pressure in the green bottom port of Figure 2. This also pressurizes the gray outlet of N75 leading to the actuator (Pressure Unit) in Figure 1. Once the air pressure in that actuator overcomes the spring pressure, the Waste Gate opens and allows some of the exhaust gases to bypass the turbine wheel. However, this action alone would open the Waste gate at lower boost pressures than are desirable. Here's where N75 comes in.
Notice the Restrictor in Figure 2. It allows only a small amount of air to enter from the green port below. As a, result the pressure above the Restrictor (that goes to the Waste Gate actuator) can be regulated by bleeding off controlled amounts of air through the left side purple port of N75. The bleed-off rate is controlled by how far the electric coil pulls up its central plunger, allowing air to escape under the blue cap at its bottom.
When you step on the accelerator, boost builds up, and so does the pressure in the green bottom port of Figure 2. This also pressurizes the gray outlet of N75 leading to the actuator (Pressure Unit) in Figure 1. Once the air pressure in that actuator overcomes the spring pressure, the Waste Gate opens and allows some of the exhaust gases to bypass the turbine wheel. However, this action alone would open the Waste gate at lower boost pressures than are desirable. Here's where N75 comes in.
Notice the Restrictor in Figure 2. It allows only a small amount of air to enter from the green port below. As a, result the pressure above the Restrictor (that goes to the Waste Gate actuator) can be regulated by bleeding off controlled amounts of air through the left side purple port of N75. The bleed-off rate is controlled by how far the electric coil pulls up its central plunger, allowing air to escape under the blue cap at its bottom.
Last edited by onepoint8tee; 08-17-2010 at 08:24 PM.
#4
08-17-2010, 08:50 PM
You are welcome. So what chip do you have? Because there is no way you would be foolish enough to try this with stock tuning.....?
#5
08-17-2010, 10:23 PM
haha thank you. of course not, come on now! i bought this a4 from one of the guys with ap tuning. its got apr software, test pipe to 2.5" exhaust, aluminum flywheel, with stage 4 spec clutch (i know specs blow), bailey diverter, apr boost guage, and an intake
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