In most of the installations I've heard about on here the boost controller pressure/vac line is plugged into the nipple under the upper intake manifold that used to supply the VFAD.
Having a pressure gauge on the outlet of the turbo enabled me to see what was going on on both sides of the throttle body with this setup.

What happens is that under partial throttle operation you get a major boost spike/surge on the turbo side of the throttle - I observed over 15PSI . Your boost controller will not see this and may even still be seeing a vacuum .
The reason it does this is that the boost controller blocks the pressure going to the actuator until it sees some boost , so the watsegate remains shut .

The solution is simple . Plug your boost controller into the other side of the throttle body .
I noticed that not only did I cure the surge but the spike in the UIM I was getting at gear changes dissappeared as well because the wastegate remains open a little longer with this setup .

This may be common knowledge to some of the more experienced people on here but I know many people are hooking the controller up to the vfad nipple so thought it worth a thread on why not to do that.

 

I identified that as one of the design faults of the original Greddy kit - it has no controller, and the wastegate actuator gets it's control signal from the LIM.

You can see that this would simply provide 100% shut signal to the turbine at all inputs, except WOT - producing whatever spikes and peaks the turbo makes without a relevant control signal.

If you used a signal source at the compressor outlet, or even between the intercooler and throttle body, the whole system would get better control.

S

 

Yes it is even in the Greddy fixes thread . But I know lots of people plumb their boost controller into the uim not realising it is the same issue . Me for one .....

 

from my understanding, the BC should get its signal from the same place the WG does. mine will be plumbed in right after the compressor outlet.

 

I prefer a location right before the throttle plate - this takes pressure drop across the IC and intermediate piping into the equation.

If you aim is to have a 'safe and controlled 10psi' you will have a very different pressure at high flow and pressure drop though the IC.

Why not control the available boost right where it matters? Who cares if the actual turbo outlet pressure climbs to 13psi to maintain your setpoint of '10psi @ the throttleplate'......

 

Yes - I have tried both spots and do get a slightly better result just before the Throttle.

 

more conservative.

 

otherway around i think . I actually get better boost at high rpm with it by the throttle body .

 

well the pressure at the throttle plate will be lower than the compressor outlet therefore if the pressure sensed at the outlet is 10psi the throttle plate may only see 9psi for example.

 

/\ true - but you just adjust your controller till you see 10 psi at the plate

 

it also cuts down on the transit time too. not sure how much quicker it would be though.

 

I have read a few other threads and it is aparent that people are plumbing into the VFAD nipple . That's good because it means i'm not the only one silly enough to do this but bad because it will be affecting turbo life and drivability for a lot of people .

 

Wait is this the signal line or the boost line?

My BC has both - so I can control the WG at the boost outlet but still tune at the UIM. Greddy Profec II FTW!

 

/\ nifty - how does that work exactly - does it mean the duty cycle can increase if boost starts dropping off at the UIM ?

Just looked up profec spec 11 and it says nothing about 2 lines . I think mine is the same as yours in fact & i only have one line ????

we are talking about the signal line BTW .

 

where exactly are you connecting it when you say before the throttle? pictures please?

 

brettus what boost controller are you working with?

 

/\ currently the profec B spec 11

 

here ya go . I'm also supplying the boost control valve from here as the pressure is lower here so (in theory) I should get more boost at high rpm.

 

where does your jet air hose go? isn't that where it connects?

 

I have it on the vac side and have a check valve to stop backflow ...

I think it is ok in either posn. but needs the check valve if put on vac side .

 

oh ok. cool.

 

Uh, whut?

Boost control solenoid MUST go before the throttle body, preferably at the turbo discharge.
Boost senor for the controller MUST go after the throttle body or it won't give you proper response and will be laggy as crap.

 

hmmm seems we have a dilema here .
I can tell you this - I originally had the sensor after the throttle body and saw 15PSI before the TB while after the TB was still in vacuum .
Now I have it in the position shown above and see whatever my controller is set at before the TB and vacuum after under partial throttle .

When you think about it - plugging the sensor for the BC AFTER the TB is much the same as plugging the line supplying the WG actuator AFTER the TB . Which was the reason for Greddy fix #2 .
Why ? As i understand it , the sensor tells the boost controller when to start operating the solenoid . If it sees no boost the turbo will keep spooling under partial throttle.

 

Because we don't care what the "boost" is before the TB.
The TB is a partial restriction, even when you are WOT.
The "boost" there is not an indication of flow.
Who cares if the pressure before the TB is 5 or 6 PSI above the pressure going into the motor? When you modulate the throttle, the total flow will be controlled there, so you want the turbo to all be working to produce the appropriate maximum flow, regardless of the resultant pressure.
Pressure is NOT flow. How many more times does this need to be pointed out?

 

I'm talking about partial throttle only - so we are not concerned with making power . I just thought it was a bad thing to see 15 PSI in the system before the TB when you are not trying to make power ?