Vf52 serious boost creep

[smokee_won]

Thanks for the close up of the Maddad. The wastegate vent tube does not mate smoothly with the flange nor is there any radius on the plate entering either hole. I see that the flow divider has been removed as well. Removing that plate and having the flat gate assembly deflect flow across that gap into the turbine exhaust as it rotates is an issue. Only when the gate is wide open are you not choking the waste gate inlet tube with turbulence cause by deflected gases and even with the door open you've got barely enough room for the gases to get past it into the vent tube. Try porting the flange of the DP and add somoe open area leading into the vent pipe on the side where you used to have the divider.

[Burba88]

I pulled the trigger today and ordered a GS EWG ! I can't wait to put it in this weekend and get my car tuned finally !!

[RabidWombat]

Definitely seems like some issue with the combination of VF52 + Divorced DP. Everyone who reported issues in this and the other thread had the divorced DP.

 

Its possible that the stock wastegate just doesn't like that configuration. It wouldn't be too surprising since it was never designed for that.

[DeltaNu1142]

Thanks for the close up of the Maddad. The wastegate vent tube does not mate smoothly with the flange nor is there any radius on the plate entering either hole. I see that the flow divider has been removed as well. Removing that plate and having the flat gate assembly deflect flow across that gap into the turbine exhaust as it rotates is an issue. Only when the gate is wide open are you not choking the waste gate inlet tube with turbulence cause by deflected gases and even with the door open you've got barely enough room for the gases to get past it into the vent tube. Try porting the flange of the DP and add somoe open area leading into the vent pipe on the side where you used to have the divider.

Interesting... there's no mechanical interference with the WG, but I see what you're saying. What about a home (read: Dremel) port job? I'll have to do some research.

Definitely seems like some issue with the combination of VF52 + Divorced DP. Everyone who reported issues in this and the other thread had the divorced DP.

It's true; look around, especially on NASIOC, and you'll see lots of info about it. That's why when my tuner mentioned boost creep, I thought about the DP first... but that divider had already been removed. My main issue was the shredded air line, but I can see some opportunities for improvement as smokee mentioned.

[smokee_won]

Another mechanism that may be affecting you is reverse flow in your vent pipe. With that divider missing the lower pressure inside the turbine exhaust chamber is going to draw gases back up the little wastegate pipe while the wastegate is closed. Exhaust flow is slower in the big pipe where the little pipe joins to it than it is at the turbine exit.

Since there is no plate to separate the big and little pipe, what is supposed to be one system is turned into something else.

A system where in you have a 'separately plumbed vent line and separately plumbed turbine exhaust' on one downpipe, is turned in a system with a chamber that shares a common low pressure area in the worst possible location of that downpipe.

If we say that pressure at the top of the downpipe in the area of the big pipe is "A", and pressure inside the big pipe where the little pipe attaches to it is "B". B>A; this is so because the gas is cooler/denser, and it is moving slower at B then at A. The differential pressure that normally exist between those two points is of no consequence because it is in the same pipe and that pipe is open to atmosphere down stream of both A and B, (which is at a for lower pressure than both). A divided pipe DP when attached should have pressures A and B where it meets the turbine housing. B in the little pipe and A in the big pipe. Not having a properly designed divider plate will turn any of the dual pipe DP's into an utter failure. Sticking a small pipe from pressure region A to pressure region B will cause flow from the area of higher pressure to the lower one. Instead of having an excellent scavenging turbine venting system (wastegate path) because the pressure/gas velocity before the turbine is higher/slower than it is way down the DP where the little pipe is attached, you end up with a backflowing turbulence inducing mess in your wastegate system before the gate is even open. As soon as the waste gate opens and deflects it's exhaust gases into the big pipe side of the mounting plate you entrain the gases from the little pipe into its high velocity flow with the result that you increase the backflow in the little pipe. So now the wastegate continues to open and the gas out of it hits the gas coming up the little pipe and all the gases in the vent path stall. The gas inside the wastegate channel can't vent past the turbine properly and you get boost. Boost spikes, boost creep "R" US for anyone not aware of this before they buy a pipe that has to be modified because it was not designed and tested on the turbine they are using.

[smokee_won]

As far as creep goes, if I got my hands on a used dual tube with a nice thick mounting plate I'd ramp out the vent side to increase the cavity size in the area of the gate arc. That swinging gate gets in the way during operation and there needs to be a larger space for the gases to get around it. Tube is great, you just have to get past the swinging barn door to get into it. I also think that welding a small brace on the tube, cutting it and welding close the big pipe might prove interesting. Or maybe installing a solenoid actuated dump valve in the small pipe and check the boost control that way first to see if it is more stable. Dumping the internal to atmosphere might be the ticket but the divider would have to be sealed well or there would be an exhaust leak all day long and when it did dump it would be just as loud as an external.