Antilag and blow off valves

[Lazy6]

Hi team,

I have an Evo 6 with a Link G4+ installed and it has been tuned by Possum Bourne Motorsport here in New Zealand. The car has a few bolt-ons but still runs standard internals and turbo. 

It's been tuned well and runs really nicely. However I do have a disappointing issue with Anti-lag when used in conjunction with a blow off valve. 

The anti-lag is configured around using the Idle Control Valve to bypass the throttle body and allow air into the engine which is ignited with some timing changes to get the turbo to create boost while off throttle. But because the throttle body is closed there is still a pressure differential between the manifold and the charged cold side and the boost all flows out of the BOV. 

The above scenario is actually fine. It's better the boost flows out the BOV rather than backwards out of the turbo and creating compressor surge. 

However, the problem I have is part throttle usage. During engine braking into a corner, the anti-lag fires, the BOV opens and the turbo spins. But as I apply the throttle, the BOV remains open or flutters and it causes the car to jerk about undesirably. If I go to wide open throttle the BOV closes. But at any part throttle usage I have the issue as described above, which stops me from rolling-into the throttle as I round corners. 

I'm running a Tial 50m BOV with the stiffest spring they provide. This is a street car used for occasional track days so do not want to disconnect the BOV and blank the hole. 

Help here would be appreciated in how to deal with this issue!

 

[Adamw]

This is not something I have experienced before but here's a thought:

What about a controlled "leak" like my drawing below.  Under relatively steady state conditions the vacuum/lower pressure would "leak out" of the restrictor so BOV will stay closed.  Under sharp transients the leak through the restrictor wouldnt be fast enough yo upset the pressure differential so BOV should still act as expected.  Restrictor size would be trial and error.

 

 

[Ducie54]

You could also included a purge valve in the vacuum line. That's if u had some spare outputs, plus u could add conditions.

[Grant Baker]

You could also use a 3 port solenoid to control the "leak" from that line?

[Lazy6]

Having a solenoid control the pressure signal to the BOV could be an idea. It would be tricky to tune because the pressure line to the BOV carries both negative and positive pressure, and both are needed for operation of the BOV. 

It would need to limit the amount of negative pressure reaching the BOV under part throttle operation only. Is that something that could be done?

Or maybe I just need to find a stronger BOV spring. As I said, I'm already using the biggest one Tial sell, but maybe I can get a stronger spring from somewhere else. 

 

 

[LilBicG69]

So I'm building my own version of the gmc typhoon with my blazer I got a 46/50/51 turbo and another 4.3 motor that's around 70k miles instead of the 200k mile factory motor in my blazer. I want the turbo flutter that happens when you dont have a BOV but I want antilag for the fire possibly a 2step, but can I run antilag and or a 2step with no BOV

[motomattx]

You understand that the turbo flutter that you describe is compressor surge and that compressor surge is damaging to a turbo?

[Adamw]

7 hours ago, LilBicG69 said:

So I'm building my own version of the gmc typhoon with my blazer I got a 46/50/51 turbo and another 4.3 motor that's around 70k miles instead of the 200k mile factory motor in my blazer. I want the turbo flutter that happens when you dont have a BOV but I want antilag for the fire possibly a 2step, but can I run antilag and or a 2step with no BOV

To answer your question, you do not need a BOV for either 2 step or Antilag.  

However, it sounds like you are mixing up some terminology here.  "Antilag" in most ECU's is a strategy used to keep turbospeed up during high RPM throttle closed overrun conditions (i.e it is only active when the throttle is closed and RPM is high - say for instance lifting off coming into a high speed corner).  Typically this would only be used on rally cars, as it generates a lot of heat all the hot components give much shorter life and also you have no vacuum for brakes etc so it needs significant modifications to support it.