Wastegate hose install
 

I am installing the rx6b kit in my fd, and I was wondering the pressure hose for the wastegate, that has to be connected before the throttle body right? Or does it not matter?

Thanks,

Ravi

I believe it should go on the manifold since placing it before for the butterflies or intercooler could cause the WG to receive a pressure signal that is different (higher) than the pressure in the manifold.

check out the diagram like 2 threads below
you want it before the butterflys, that is how it is stock and every boost controller diagram I have seen shows it this same way.

I dont know why, that is just how I always see it.

Bob

I have been reading about boost control solenoids for the better part of the afternoon and noticed that every single boost control diagram I've looked at has the line plumbed in near the turbo. I came back here to inform you of this, but it looks like Bob beat me to it

Frankly, I am still not sure why pressure isn't taken from the manifold. Assuming the WG spring is 7lbs, and there is a 1psi pressure drop across the intercooler, then when the inlet pipe to the IC is at 7psi the outlet pipe will be at 6psi. That would place manifold pressure at 6psi, assuming the butterflies don't provide any additional reduction in pressure. Therefore, if the line to the wastegate is connected near the turbo the wastegate will start bleeding off pressure when the engine sees 6psi not 7psi. Obviously this can be compensated for with an adjustable boost controller, but it still seems odd to take pressure from this point when a more accurate measuring point(the manifold) is approximately the same distance from wastegate. Here are the possible reasons I have come up with:

1. Lag in response due to the distance between the measuring point and the turbo.

2. Connecting the line to the manifold would expose the WG diaphragm to Vacuum under certain conditions and this may damage the diaphragm. Although, it seems like issue #2 could be resolved with a check valve.

3. Most cars do not have a large enough air supply port on the manifold for the wastegate. Tial recommends that an 8mm line be used with their wastegates according to a member on the AEM board. If this is the only issue I wouldn't mind drilling and tapping a new hole in my manifold.

4. The spring pressure determines when the wg begins to open, but not necessarily what the boost will be regulated to. Therefore there is no real point in trying to make the line pressure correspond with spring pressure.

I am particularly interested in this subject because once my car is tuned I am thinking of regulating boost solely by the wastegate spring since I only adjust my boost settings when I need to compensate for warmer or cooler weather.

This topic is covered in Corky Bell's "Maximum Boost".

Most wastegate vacuum source points are at the turbo or on the turbo compressor housing itself.  This point gives you the fastest WG response, as this is where the boost will start building the earliest.  The drawback is that this is also the area where the intake charge will be the hottest.  Corky Bell mentioned this, but I have never heard of a wastegate failing due to the hot WG vacuum source - maybe the hose will fail?

With the wastegate vacuum source point located aft of the TB in the intake manifold, this would be the coolest (maybe direct after the IC could be argued?) point for WG vacuum.  This happens to also be the last area the boost will "hit".  Be ready for boost spikes if you're going to do this.

I don't think it's a matter of "accurate" WG spring boost levels, as most aftermarket external WG's come with adjustable tension or just run a boost controller.

We ran into some direct experience with this topic trying to tune a built 13BT on an FC running an H-trim compressor upgrade.  Due to a restrictive exhaust, the turbo only managed to produce 2.5psi of boost with the (stock) WG actuator vacuum source coming out of the turbo compressor housing.  We moved the WG vacuum source to the intake manifold aft of the TB (in the intake runners), and boost jumped from a solid 2.5psi to a 5psi spike leveling off at 4.5psi.  This gives you some idea of the relationship of WG vacuum source versus boost produced by the turbo.


-Ted