Hello,
I have a twin turbo extreme aps kit, modified with smaller turbos, two gt2554r, when I increase the spring pressure, the pressure does not increase... the pressure rises to 10 psi and after 3500~4000 rpm the pressure drops to 5 psi or less... any ideas?

knowing that the pressure problem which does not exceed 10 psi already existed with the original turbos

a boost leak seems unlikely to me otherwise it would not build up pressure or it would build up very slowly and it would not produce a drop in boost at 3500 rpm

​​​​​​I don't have a fuel return system and I run on E85, could that be the problem?

 

What is controlling the boost on this? Wastegate pressure alone?

 

yes two external wastegate only

 

It definitly could be a boost leak and those tiny turbos are masking it because they are so efficient at low rpm. Then at higher rpm with more flow requirements the turbine side is running out of capacity/efficiency.

It could also be your waste gate plumbing is backwards. Can you draw a schematic of your wastegate lines (and be absolutly sure what you draw is how they are actually run)

 

This is exactly the kit I have as in the photo and the wastegate is mounted in the same direction, for the leak I will look for a hundredth time 😅

 

Lol you can't see the wastegate, bc,or solenoid plumbing at all. Draw up how it is actually connected so we can help trouble shoot. (Not how someone else says it should be)

 

Here is a drawing of the assembly

 

Do you have any sort of boost controller in the mix? (I hope so) What lb springs do you have in it currently. Definitly sounds like something is not right. If your mac solenoid is plumbed backwards it could be bleeding wg pressure instead of keeping the wg closed when it goes into the gain loop. Basically where it is fighting boost reduction with rpm is actually causing it to get worse and worse with time.


My first thought would be to put a low spring in (6 psi or so) and then disconnect the top of the wastegates entirely and see how the boost behaves. It should get to six and then hold there with just a little bit of boost taper to 4.5 or 5 at redline. This would indicate an issue on the line coming from your intake.

 

I don't have a boost controller, I must have around 16 psi in the spring, I don't think my problem comes from the supercharging side, in fact when I reach 4000 rpm the pressure collapses to 0, when I look at the logs the base fuel schulde collapses too, it's as if the car was restricted from 4000rpm and 10~12psi. I'll try to make a video during acceleration with the pressure gauge and the meter to better illustrate my problem. I'll still try as you say to remove the pipe that connects the wastegate to the intake while plugging the intake side so as not to create a leak.

 

You should not have two vacuum lines running to your waste gate if you do not have a boost controller. The pressure differential of your throttlebody and intercooler is opening your wastegate.

 

Now, what about the blow off valves. How are those hooked up?

 

They are connected exactly as in your image with the difference that each turbo is connected to its wastegate

 

You have an extra line going to the intake in your photo

 

I removed the line that goes from my wastegate to the intake and that didn't change anything, more than a loss of pressure it's a total loss of power that I have at 4000 rpm on my logs everything collapses at the same time at 4000rpm whether it's the bfs, the shift, the inj duty and the turbo pressure on the gauge...
it's a problem that I didn't have with my bigger turbos which charged from 4000rpm until the breaker, something is restricting the car but I can't understand what it is

 

post some .csv files

 

here is a log of an acceleration

 

You have the lines going directly from the turbos to the bottom of the wastegate ports?
You have your BOV line attached to the intake manifold after the throttle plate?

 

no it was connected before the throttle