I was porting my S5 wastage today. I did a fairly large port on the short passage without problem. I did not do any porting on the larger passage. When I was done we shut the flapper door and noticed that I could see some light (when we lit the back of the ports) from around the larger passage. The flapper door has some rotational play in it plus the shaft allows the flapper to move in and out a bit. This combination was the casue of the "winking passage" with the flapper door fitup. I am now concerend that when I put this turbo on my car that I will be loosing some boost becasue of this potential leakage point. Is this normal or do I need to fix the flapper so it can never have the "wink" effect?
Thanks

 

how much are we talking about? a tiny sliver will hardly leak boost so if it is a minor gap i wouldn't worry about it.

 

I would guess if the flapper has a leak...its going to lead to turbo lag.

You need some overlap to help that door seal. So, if your seeing light you have no overlap anywhere.

Just put a bigger flapper on.

James

 

A wastegate leak will lead to increased lag, but not lost boost. Replacing the S5 wastegate flap with abigger one is going to be very difficult, so you'll have to either live with it or get a new turbine housing.

FWIW, when I ported the wastegate on my yet-to-be-installed S5 turbo I painted the underside of the flap with white paint then closed the flap while it was still wet. This let a nice white mark around the ports as a guide. I ported up to ~1mm from the edge of the mark to get a good seal. This allows for a bit of movement in the flap.

You should port the opening on the long passage too. You can't get very far down but you can enlarge the opening quite a bit, which does improve flow.

 

Jason, Why would I not loose boost and only get lag fom this problem? Is the reason becasue at full boost the door is open anyway? Just curious so I can understand the function and sequencing of the wastegate.

The leak is about 1mm max around 90 degrees of the larger port. I guess it is not very big then. I am thinking of placing a c-clip around the flapper shaft on the outside of the manifold. Hopefully this will keep the door from swiveling over to this gap condition.

Thanks

 

good idea.

 

Because air will get past the wastegate which stays closed until you reach whatever psi your wastegate is set to open at. Hence you will not loose boost becouse at some point your exhaust gas will spin up the turbo to 8psi, then the wastegate will open only enough to bypass a certain amount of exhaust to keep you boost at 8psi. The larger the wastegate port the less the flap has to open to keep your boost down.

 

If the hole is as tiny as ur describing it. Don't even worry about it, yes it will give you some turbo lag wich you will only notice in a Dyno. (wich will be very minimal) Or you might not even notice it at all. But for sure you will not notice any lag if your only street tuning.
Trust me i'm an expert.

 

That or you can use the discolored outline that's already there from the carbon/exhaust funk that's cooked in, then scribe that line. It also already incorporates the "slop"

 

the seating lines often are hard to see or are not a true the the actual seat of the door.

 

I agree with Karack, the lines can be hard to see. What I would recommend is that you backlight the port and pay close attention as you move the flapper door in and out on its shaft and in rotation around the pin. This will show you the best / worst case flapper coverage.
Thanks for the explination on funtion....it helps to know that.
Since I have time and the tools I am going to try and ensure 100% coverage. Has anyone ever removed the flapper door assembly? It looks like I would have to grind the the lever rod weld off and then remove the flapper shaft assembly. Anyway. I will try and post some pics of the prob later for others to consider and I will post the solution too.

 

I over ported mine just a bit on the side which faces the downpipe. I kind of made one side transition like a velocity stack or something so there isn't a lip.

I had some serious boost creep problems on the S5 housing before.

Yes it does lose some of the spooling punch but it's not noticiable in my car.

After the porting I held 6psi easily until WOT in 5th then it creeps up 1 psi.

I get 10psi(using mbc) around 3500-4000 rpm easily after the porting so I consider it a fair trade.
controllable boost for a slight increase if any in spool.


: edit :
Oh yeah I back cut the flapper too to increase it's swing.

 

Normally when the wastegate is closed all of the energy in the exhaust gases are being used to drive the turbine. The more gases passing through it, the faster it'll spool up. In your case a small amount of that enegy is bypassing the turbine, so it won't spool up as fast. Once the wastegate open everything is acting like it normally would like driftin8ez said.

A small leak will only make a small difference, but to say you'll only notice it on a dyno is a complete load of BS. That's the last place you'll see it. Dynos are completely usless at showing boost transients. Full throttle power runs in a high gear means the turbo keeps up with the engine and lag is of no consequence. On the street when you're accelerating in lower gears any turbo lag is far more noticable and undesirable.

Yeah, okay...

By incorperating the slop in all directions it actually makes a line bigger than the flap's coverage, so if you use that as a guide you need to know how far to stay clear of it. Once I had my white marks I moved the flap around to see how much sealing area I had to leave to avoid leaks.

But if you needed a boost controller to get the 10psi you wanted then the trade-off is a bad one. If you'd only ported enough to keep a good seal and got say 8psi instead of 6psi, you'd still be able to get the 10psi you want and improved spool.

When you see the DP I'm making for my S5 turbo you'll see why this wasn't necessary for me. IMO people spend too much time concentrating on the wastegate ports themselves and ignore the other things restricting wastegate gas flow.

 

The trade off is a great one.
Yes with a stock wastegate I hit 10psi easily BUT it was uncontrolled boost.
It would creep past 12+psi with half throttle. Something I do not like to see on stock injectors.

It's a safety mod more than performance.

I ported the wastegate so the turbo could manage boost correctly. I then used a MBC to set it to my desired level. I prefer a constant boost level over random quicker boost (although not much quicker).

I over did it because this is a daily driver and down time is a big factor. I don't want to have to install then remove the turbo multiple times to see if I did it enough.

Also even after the porting w/ the MBC set to 10psi I still hit 11-12psi @ WOT in 4th/5th.

I wanted the closest to stock wastegate control so that when I hit the higher boost numbers it would stay close to that number. If I ported to get near 8psi creeped instead of 6psi I might have hit 13+psi now.

 

It's not a trade-off I'm willing to make, which is why my wastegate ports are as big as they can be without leaking and why I'm improving wastegate flow in other ways. When the turbo and new DP get onto the car we'll see how successful it is at holding the 10psi I want.

 

With incorporating the slop, you have a much better chance of no going too big. Then after the hard cut is done, slowly bring it open some. Just like porting a housing.

the problem we hear all the time is "I went too big" Using the outline that's burnt in will help with eliminating this.

I've ported 3 S5 turbos in the last 2 mouths, & many more over time. To date I'm yet to have a problem with seeing the outline that's already there. Scribe it, cut in, feather it, done.

 

What about with the flapper closed, "slop" it all the way to one side with your hands (wearing latex gloves) and hit it with spray paint, then slop it to the other side and so on until you've painted every where the slop is, then port it out. Wire wheel it before it goes back together to keep down smoke.

 

Not saying the exhaust burn marks aren't visible, but maybe for newer turbo's. Good condition or brand new maybe.

 

Why not, you can add as many extra steps that you need to do it right. I've just never needed all that.

 

I wouldn't worry about it.
The lag induced is not going to be significant.
Even if you went 1mm larger than the flapper, I doubt most people would feel any lag difference.

Just enjoy your car!


-Ted