Author Topic: Boost creep  (Read 945 times)

Offline dub-disaster

  • Members
  • *****
  • Posts: 1623
Boost creep
« on: October 23, 2011, 09:53:55 pm »
Hi all,
   Got a forge actuator on my k03, currently got the weakest spring in there think it's the "6psi" spring. Had it set at around 6-8psi which is fine spools fine holds that boost all the way untill about 5.5k rpm where the boost starts to creep up and up noticed it ran to about 17 psi for a couple of seconds today so I stopped and lowered the boost pressure to around 5-6psi it. Still does the same and once 5.5k rpm hits the boost starts to creep up.

I read up onthe net about boost creep and it's caused by the wastegate not being able to flow enough of the exhuast gas into the exhuast and therefore controll the turbine speed under higher loads.

The soutions to the problem include using an external wasgate, having the internal wastegate enlarged (although this makes the exhuast housing prone to cracking). Not sure if it could also be reduced by increasing the boost pressure therefore the waste gate would stay closed for longer although if it has crept to almost 20 psi I can't see turning the boost up stopping it as it will still creep up as the waste gate is still not going to flow enough.

Could this be caused by adjusting the actuator rod, or the rod being to short when adjusted up so that the waste gate is never fully open, therefore doesn't flow enough? This is what I think may be happening as if the wastegate can flow enough for a 1.8t passat surely a 1341 couldn't flow enough to cause problems.

I also wondered about the cam (268/268) I have a vernier and have timed it up to the shrick timing figures but could this be causing the engine to flow the alot more air up top, could "swinging the wheel" or having it set up correctly help?
   
Just wondered if anyone has had this before, and how they solved it.

For the record it wasn't running lean at any point as it runs very rich in full boost anyway (10 on my afr) although I shan't be reving it that high again untill I have it custom mapped. Just want to eliminate as many problems before then.

Offline cheys03

  • Members
  • *****
  • Posts: 794
Re: Boost creep
« Reply #1 on: October 23, 2011, 11:15:15 pm »
Interesting problem! I'd perhaps start by making sure the actuator rod is adjusted to leave the wastegate the greatest chance of opening fully, without making it so slack that it flaps about as it opens... if you haven't already. I take it your actuator vacuum hose is just a straight hose, no bleed valve etc?

Offline Yoof

  • Traders
  • *****
  • Posts: 2336
  • I know naathing..
    • Polo Performance Parts
Re: Boost creep
« Reply #2 on: October 24, 2011, 07:04:17 am »
You won't have this problem once you increase the spring tension (i.e run more boost).