Wastegate Leaking Perhaps?

[Redback]

Hey guys,

I have had the larger flapper and wastegate ported on my exhuast housing. While I had it off again I thought id check the wastegate for leaks. How well is the flapper meant to seal against the housing? With the actuator on I used compressed air and blew it around the flap. I noticed some air was leaking back through to the housing?? Is the flap meant to have a real good air tight seal on the housing or is it normal to bleed a bit of air through?

[Benny]

I don't have a definate answer for this but after looking at wastegates on turbos on a number of occasions I can't imagine they'd seal that well. It's just steel on steel. I'd imagine there would be some leakage past the flapper but as long as it stays closed and directs majority of the gases through the turbine on boost then it'll work good enough. Just my thoughts, not sure if I'm right or not.

Benny

[bjc]

Both surfaces are machined flat so I would think that it would have no leakage once the actuator is adjusted properly otherwise why machine then!

We are having this problem with ray076's turbo, apart from the fact that it was flowed way to much directing mass amounts of gas to the wastegate it has virtually no machined surface on the housing and therefore leaks on the top edge, feeler guages tested that we had a decent gap!

Now whether its the porting gone to far (which I think) or the leakage of the flapper, the tuner just cant ramp up the boost quick enough (8psi max by 3000rpm!) and this was with the supposed 12psi actuator that came with the turbo which was actually over 20psi tested!

I had wire wrapped around the flapper arm to hold it completely shut under any condition and it showed the same lazy boost...

[Redback]

The original machined surface is still there. It has probably at least 2mm of surface. What kind of gap did the feeler guages give you? I dont have any real boost ramping issues otherwise Jim @ Tunehouse would have realised on the dyno.

[45T-XR]

It depends on how much work went into the the finish of the flapper and housing, Judging by what Ive seen so far they would hardly seal airtight, for the metal-metal surfaces to seal they would have to be highly polished.

[Redback]

I took the Turbo back to Precision and John assured me that they do not seal airtight. You are always going to get some leakage around them

[45T-XR]

Cheers, I suspected as much, Ive seen metal to metal seals before, for example in earthmoving equipment called duo-cone seals, they seal and separate usually the hubs/final drives from the brake hubs. But the quality of the finish on them is quite high, nealy a mirror finish.

[Ralph Wiggum]

the wastegate only was too divert the bulk if the flow of gas it doesn't need too seal air tight.

if you want a super tight seal change too any external gate with a taper seat seal.

the are plenty of non wastegate related issues that can cause lazy boost response

tuning being the most obvious

[bjc]

I can guarantee in ray076's case lazy boost is not to do with the tuning! If you believe that the wastegate leakage wouldn't be a problem then it would be the porting has been severly over done on his housing by another workshop as he bought the turbo from another member on this forum.

[Ray076]

The joys of turbo's..... Oh the pain. Dont buy second hand is my advice and make sure whoever modifies the turbo has a good reputation..