What's wrong with my Wastegate?

[iwalton]

I've got a pretty much stock 1990 tsi 6bolt engine in a 1994 body. I have a 3 inch turbo back, and blocked off the bcs (broken). and recently put in an aftermarket boost gauge. I've had to drive it (because it's my dd) and below 4000 rpm at wot, it holds around 10-11psi and then just after 4000 rpm, it rips up to 17 psi! Ideas?? What's the problem?

 

[LiquidX]

If you are WOT the whole time then it just sounds like spike or creep issues. What does it do after it hits 17psi?

 

[JusMX141]

Your wastegate hole probably looks like this:

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No seal = inconsistent boost pressures generated.



...or what Scott said above. Lack of backpressure = boost creep.

 

[iwalton]

If you are WOT the whole time then it just sounds like spike or creep issues. What does it do after it hits 17psi?

Ok, I understand this. It will still tend to keep building more boost after 17psi is reached. I'm just a little afraid of wrecking something...? But shouldn't my wastegate automatically start venting at anything over 10-11psi?

Wouldn't a wastegate hole (crappy seal) mean it would vent at a lower psi?

 

[LiquidX]

Boost creep - When the path of least resistance is through the turbine wheel instead of the wastegate hole.

What happens is the wastegate becomes a restriction even when open so the exhaust bypasses it and just goes through the turbine which builds more boost. There are various reasons why you could have boost creep which can be from having a free flowing exhaust (lack of back pressure) or just having a bad entry into the wastegate inlet which requires porting. It's very common with the 16g turbo hot sides.

To add to your question with Justins pictures, if the cracks are open when cold, you will be at lower pressures as the exhaust is leaking past. When the metal heats up, it will expand, sealing the leaks and allowing more boost to be built.

More info from you would be needed to make a accurate decision on that possibility however.

 

[iwalton]

Boost creep - When the path of least resistance is through the turbine wheel instead of the wastegate hole.

What happens is the wastegate becomes a restriction even when open so the exhaust bypasses it and just goes through the turbine which builds more boost. There are various reasons why you could have boost creep which can be from having a free flowing exhaust (lack of back pressure) or just having a bad entry into the wastegate inlet which requires porting. It's very common with the 16g turbo hot sides.

Right on, totally getcha! I've got a 14b turbo, so should I port the wastegate or get a bigger aftermarket wastegate, or what exactly would be the best option there?

 

[LiquidX]

It's an option to port it out but I'm leaning towards the 3" exhaust being the cause. Did it do it before the exhaust install?

I'll leave the rest to Justin if he comes back in. Turbos are more his thing