Help! Losing Boost

[Sparki_D]

Hey guys,

My mate just rebuilt an RB30 using the RB25 head, its running a t3/t4 garrett turbo. A turbosmart pro gate is installed.

The problem being is the car loses boost, at the moment it will boost to 18psi and radically drop to 14psi where it will hold. The boost controller has been changed from a HKS EBC to the simple turbosmart T-Piece, but this has had no effect.

Before the external wastegate was installed the motor would only hold at 12psi.

Any ideas you guys could give me would be greatly appreciated.

* The boost we want to run to the motor is a constant 20psi.

[Steve]

A stiffer wastegate spring, as close to 20psi as possible, this will mean your boost controller has less work to do.

[Sparki_D]

From what I gather from turbosmart you can only get a 12psi or 14psi spring. The 14psi is installed. Where/how do you get a different spring?

[Steve]

I dont know sorry. It was a suggestion as a quick fix. Reallistically I think there is a problem somewhere else, as I can get well over 10lbs adjustment with my external gate and it holds fine - I am not sure what spring it has, but I have run as low as 10psi, so softer than the one your mate has.

How is the gate plumbed up? Was the gate new, and if second hand, did you have it checked out before fitting it?

[Sparki_D]

The gates plumbed up, it currently wastes to atmosphere, its brand new, and its been plumbed up to be controlled by the EVC, it was professionally installed, as well as tuned, after a smoke test they still cant find the leak.

I believe that the problem lays somewhere with the internal wastegate on the turbo not being disconnected correctly. Could this be possible?

[Steve]

What I dont understand is that it is making 18 and then dropping.

If it was internal gate, did they weld it shut, or wire it? If it still has the standard acutator in place, it is possible its leaking boost.

As for professionally plumbed, I have had some 'professionals' (they certainly charged like professionals) do some pretty ordinary things. When I had my gate first plumbed, he did it wrong and I had to sort it myself. That is only one example of several. Not that I am saying these guys didnt do a good job, but sometimes it pays to check the basics.

[Cubes]

I had a Blitz SBC-iD EBC that had 2 modes.

Auto - Learn boost curve and adjust to suit

Manual - Percentage of max boost available.

The auto mode would manage to hold boost at 16psi up over 5500-6000rpm BUT it was struggling as the boost curve (as per the graph display) was a little wavy. The solanoids also showed that they were basically 99% closed over 5500-6000rpm in order to hold the boost I was asking it to.

The manual mode would have boost come up (16psi) and hold perfectly flat until around 5500-6000rpm it would then drop to around 13psi.

I've also had a VG30BB turbo that has a large .81 or what ever it is exhaust housing. Exactly the same thing. Boost drop over 5500-6000rpm. I tried both the RB20t 10psi wastegate and the VG30 6-7psi wastegate on the VG30 turbo.

The weaker wastegate (VG30) the most boost I could get the car to hold with a bleeder or in manual EBC mode was around 10-11psi, in auto mode it would hold ~14psi but not 16psi.

I think its got a lot to do with the strength of the wastegate spring not so much back pressure as back pressure is always going to be there. Tim from RPM did a comparison and saw no difference once on full boost between a ~.81 & ~1.01 with regards to back pressure in the turbo housing, it always hung around the 2 x inlet pressure. This was on a 900hp VL Turbo.

[BenA31]

sounds little like its spiking. how long are the hoses? maybe they need to be shorter otherwise yeah probally a problem with the actuator spring