Vacuum line routing - BOV & WG
#1
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My turbo install is almost complete. I've been doing a lot of reading here about where to take the vacuum source for the wastegate and bov off of and have plumbed mine as follows, I'd like your input on this.
Leg 1
Off IM right behind TB -> T-fitting feeding 50mm TIAL BOV and do-dads on pass fender
Leg 2
Off IM right behind TB -> T-fitting feeding internal WG actuator and MS (line for the MS also feeds boost guage)
Do you think putting the WG in line with the MS and boost guage is too much seeing as how I'm dependant on the WG to not blow my motor up?
I originally wanted to tap into the brake booster line but couldn't find the right T's for it.
Leg 1
Off IM right behind TB -> T-fitting feeding 50mm TIAL BOV and do-dads on pass fender
Leg 2
Off IM right behind TB -> T-fitting feeding internal WG actuator and MS (line for the MS also feeds boost guage)
Do you think putting the WG in line with the MS and boost guage is too much seeing as how I'm dependant on the WG to not blow my motor up?
I originally wanted to tap into the brake booster line but couldn't find the right T's for it.
#2
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Wrong. You're going to murder your turbo that way and get a shitty map signal to your MS. The source for the WG needs to be before the throttle body to avoid the turbo trying to make INFINITY boost against the throttle plate. General consensus is that a fitting pre-TB and post-intercooler is best to minimize boost falling off in the upper RPMs.
For the megasquirt, try T-ing into the FPR.
For the megasquirt, try T-ing into the FPR.
#5
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The wastegate reference on a street-driven car signal shall be taken from a point in the system which is after the compressor but before the throttle body. Fittings installed upon the compressor housing itself by the manufacturer of the turbo qualify as being "after" the compressor, as they are located on the discharge side of the scroll.
Where an intercooler is present, the signal is ideally taken from a point after the intercooler. If the signal is taken from a point before the intercooler (including the compressor housing) then you will experience boost sag (manifold pressure will decrease as RPM increases) owing to the pressure drop across the intercooler, which is not a constant, but increases with the square of the flowrate across the restriction. Taking the wastegate reference after the intercooler will cause pressure measured at the compressor outlet to increase in response to the pressure differential across the intercooler, and thus, pressure as measured within the intake manifold (or at least, between the intercooler and the throttle) will remain constant.
If the wastegate signal is taken from a point after the throttle, then whenever you are in boost but are using the throttle to modulate boost to a level below the setpoint, the wastegate will remain completely closed, as the turbo will be attempting to produce an infinite pressure ratio across the compressor, in order to achieve the setpoint at a point in the system at which it cannot be achieved. This reduces efficiency, makes a lot of heat, and is just generall a Bad Thing™. This is also the reason why TPS is a critical input when EBC is being implemented inside the main ECU, using the main MAP sensor. The system must know to reduce the setpoint when the throttle is not fully open, as the MAP sensor is not seeing the true compressor pressure.
The signal to the BOV, however, should be taken after the throttle plate.
Where an intercooler is present, the signal is ideally taken from a point after the intercooler. If the signal is taken from a point before the intercooler (including the compressor housing) then you will experience boost sag (manifold pressure will decrease as RPM increases) owing to the pressure drop across the intercooler, which is not a constant, but increases with the square of the flowrate across the restriction. Taking the wastegate reference after the intercooler will cause pressure measured at the compressor outlet to increase in response to the pressure differential across the intercooler, and thus, pressure as measured within the intake manifold (or at least, between the intercooler and the throttle) will remain constant.
If the wastegate signal is taken from a point after the throttle, then whenever you are in boost but are using the throttle to modulate boost to a level below the setpoint, the wastegate will remain completely closed, as the turbo will be attempting to produce an infinite pressure ratio across the compressor, in order to achieve the setpoint at a point in the system at which it cannot be achieved. This reduces efficiency, makes a lot of heat, and is just generall a Bad Thing™. This is also the reason why TPS is a critical input when EBC is being implemented inside the main ECU, using the main MAP sensor. The system must know to reduce the setpoint when the throttle is not fully open, as the MAP sensor is not seeing the true compressor pressure.
The signal to the BOV, however, should be taken after the throttle plate.
#6
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Thanks for the help, I think I figured this out. I had a fitting on an old turbo I was able to get threaded into the turbo that's on the car, I'll use that for the WG. BOV will be off the first nipple behind the TB, MS will be fed from a T fitting in the FPR line and the boost guage will be fed from the second nipple behind the TB that also feeds the evap canister.
#11
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If the wastegate signal is taken from a point after the throttle, then whenever you are in boost but are using the throttle to modulate boost to a level below the setpoint, the wastegate will remain completely closed, as the turbo will be attempting to produce an infinite pressure ratio across the compressor, in order to achieve the setpoint at a point in the system at which it cannot be achieved. This reduces efficiency, makes a lot of heat, and is just generall a Bad Thing™. This is also the reason why TPS is a critical input when EBC is being implemented inside the main ECU, using the main MAP sensor. The system must know to reduce the setpoint when the throttle is not fully open, as the MAP sensor is not seeing the true compressor pressure.
#14
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Never do this. Internal wastegate actuators that use pressure to open the gate (that describes about 99.999% of aftermarket gates) are not designed to handle vacuum.
Over time, what happens is the diaphragm inside the actuator will pull out of the crimp that is holding it in place. And then there is nothing to open the wastegate. Well, except for the exhaust manifold pressure acting on the face of the valve itself. But you will have long since overboosted.
So don't hook your gate up to manifold vacuum, kids.
Over time, what happens is the diaphragm inside the actuator will pull out of the crimp that is holding it in place. And then there is nothing to open the wastegate. Well, except for the exhaust manifold pressure acting on the face of the valve itself. But you will have long since overboosted.
So don't hook your gate up to manifold vacuum, kids.
#17
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^ there are both ups and downs of bov placement closer to TB vs turbo.
but generally, to make your life easier, closer to tb the better. but doesnt have to be super close like literally an inch from TB, now thats just ridiculious.
mine currently sits about not sure a foot? or less from TB roughly around mid way down the rad on cold side
but generally, to make your life easier, closer to tb the better. but doesnt have to be super close like literally an inch from TB, now thats just ridiculious.
mine currently sits about not sure a foot? or less from TB roughly around mid way down the rad on cold side
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