I'm looking for peoples experiences of unusual boost leaks.

I'm battling with one on my Rev1 Turbo engine, in that I can drive and boost fine up until 14psi (boost controller set for this) and then all of a sudden there is a quiet pop and boost drops back to around 4psi. I then change gear and boost will still be stuck at around 4psi, but if I stop accelerating and then give it a couple of seconds and accelerate again boost will start to build again OK to 14psi.

This all started last year when I noticed on a track day that I was losing power at certain points, but I ended up distracted by damaged blades on my CT26 turbo and a significant boost leak, which turned out to be one of the vacuum barbs on the plenum being jettisoned. Turbo was replaced with a CT20B and the vacuum barb replaced and used to feed a boost gauge until now when i’m left with a car that drives quite well apart from this annoying boost issue.

Things I have done to try and resolve:
  • • Because the issue is reminiscent of a wastegate being stuck open I have tried three different down pipes in total, but also confirmed that wastegate is not staying open by use of a camera on it when driving. Currently have a Blitz cast downpipe fitted.
  • • Eliminated recirc valve by testing but also fitting a known working one.
  • • Replaced all couplers with silicone versions, although no obvious signs of problems with OEM rubber couplers.
  • • Last year I was using stock boost control and now I am using a Greddy Profec boost controller because of the CT20B.
  • • Pressure tested intake between turbo inlet and just before throttle body and no leaks.
  • • Pressure testing intake at entry to throttle body and into the rest of the system. A couple of small leaks spotted (throttle gasket and one chaffed hose) and rectified.


Because boost is building to 14psi and then something is opening\happening and this is dropping back to 4psi it must be something significant, but i’ll be damned if I can find it.

So wandering what experience you guys have of any unusual boost leaks ?