Wastegate troublemaker

[PorscheGAL]

Folks,

I wanted to share a recent upgrade story on my 930 in hopes it will help a fellow reader or two. I recently upgraded to a K27, Rarelyl8 exhaust, Andial intercooler and clock replacement boost gauge.

After putting it all back together, I found my boost had no end. It just kept going over 1 bar with a spring of only .8. I looked at each connection and re-tightened every bolt. I thought about the wastegate, but why would it be bad? It worked fine before all the changes. I still checked it for leaks and didn't detect any. I went further with a diaphragm and spring change and it was still boosting forever.

Today, I replaced the wastegate with a Tial. My stomach had butterflies as I exited my neighborhood in hopes of my car finally working again. As I pushed the gas, I finally felt that old feeling again; torque. The Tial was a gamble and it paid off.

The changes fixed a couple trouble points. My car did get as hot, and I have much less smoke.

My question in all this is why did my wastegate go bad? New parts or just its time to go? FYI my car has 100K miles on it.

[mark houghton]

Originally Posted by PorscheGAL

Folks,

I wanted to share a recent upgrade story on my 930 in hopes it will help a fellow reader or two. I recently upgraded to a K27, Rarelyl8 exhaust, Andial intercooler and clock replacement boost gauge.

After putting it all back together, I found my boost had no end. It just kept going over 1 bar with a spring of only .8. I looked at each connection and re-tightened every bolt. I thought about the wastegate, but why would it be bad? It worked fine before all the changes. I still checked it for leaks and didn't detect any. I went further with a diaphragm and spring change and it was still boosting forever.

Today, I replaced the wastegate with a Tial. My stomach had butterflies as I exited my neighborhood in hopes of my car finally working again. As I pushed the gas, I finally felt that old feeling again; torque. The Tial was a gamble and it paid off.

The changes fixed a couple trouble points. My car did get as hot, and I have much less smoke.

My question in all this is why did my wastegate go bad? New parts or just its time to go? FYI my car has 100K miles on it.

Stephanie, are you certain you connected the boost signal hose to the WG correctly, to the side port (the top is just atmospheric vent). If all connected correctly, then it almost has to be the diaphram ruptured.

[930LDR]

Once I went with after market headers and my K27HFS, my TiAL couldn't keep the boost under control. Had to actually install a very soft spring and an electronic boost controller to be able to reliably dial in 1 bar. Can't recall if I ran the combination with the stock wastegate or not. Too many mods over too many years.

[cl8ton]

I had a similar prob with my stock WG…pegged it at 1bar with what I was told was a stock spring.
Found out that it wasn’t a stock spring, found a NOS .8 bar spring and everything is fine now.

Problem with stock WG’s, you really cannot tell the diff visually between stock and aftermarket springs. And NOS/Even Used .8 bar springs are a rarity!

At least Tial color codes theirs.

[RarlyL8]

If you changed the diaphragm and the spring the only thing left is the valve and guide. At 100,000 miles it is likely coked up and sticking shut which would cause your problem.
How do you like the sound?

[Alan L]

Well, I was about to post a very similar query.
My lower casing on w/gate split open - so I have just fitted a new(er) one (via Pelicanite).
It looks in much better cond than my pervious.
Luckily I decided to bench test it before fitting. At 1 .0 bar (0,8 spring), it is not budging.
Heading to overboost.
The valve is nice and free.
Am I asembling this right. I even tried a softer spring - same result- 1.0 bar in can, and not budging the valve.
But I can move it quite freely by picking up the diaphragm base.
Alan

[A930Rocket]

Are you sure you are applying air to the correct port? Enough air pressure? If yes, the diaphragm might be bad.

[mark houghton]

Originally Posted by Alan L

Well, I was about to post a very similar query.
My lower casing on w/gate split open - so I have just fitted a new(er) one (via Pelicanite).
It looks in much better cond than my pervious.
Luckily I decided to bench test it before fitting. At 1 .0 bar (0,8 spring), it is not budging.
Heading to overboost.
The valve is nice and free.
Am I asembling this right. I even tried a softer spring - same result- 1.0 bar in can, and not budging the valve.
But I can move it quite freely by picking up the diaphragm base.
Alan

For bench testing, it takes more air pressure than 1.0 bar (if that's the spring you're using) to open the valve. Around 18-20 pounds should open it.

[cole930]

PorscheGAL,

I'll give you $65.00 and shipping for your broken wastegate.

Cole

[Alan L]

OK A930, if you look at left of pic you can see a bit of plastic hose on inlet to diaphragm. That is where I am pressurising. Mark, I am interested as to why it would take more pressure on bench.
I have got it working again, popping open at 0.8 bar - but I had to insert a lighter spring than previous to do it. Have not installed for road test yet.
But previously when I was checking the unit over a year or so ago (discarding an EBC) it was opening at 0.8 on the bench, and has done so for past year in car. Now I put a new valve end in, the requirements in the can seem different.
When you think about it, it is quite finnicky design-wise. You have a spring compressed to over 100lb in the can, then you are applying 11-14 lb opposite pressure to lift the valve. 11psi = 0.8 bar boost, 14 psi - 1 bar. So you are trying to tune this thing to respond within 1 psi differential. Surprising it works at all.
I will file this experience in the 'Weird' section. Am interested to see what happens with road test.
Regards
Alan

[mark houghton]

Originally Posted by Alan L

Mark, I am interested as to why it would take more pressure on bench.

A certain amount of pressurized air will leak past the valve guide and/or valve seat if it's worn somewhat, so it takes a bit more pressure than the spring is rated for to bench test. But, when installed in the car, exhaust gas pressure also plays an additive role to help open the valve. It may actually be a gas volume thing as opposed to actual pressure, but it's the combination of the two (boost pressure from the IC and exhaust back pressure) that the WG is calibrated against...to enable it to open at the specified spring tension.

I found that out when I switched to a Tial WG (purchased used), and was benchtesting prior to installing. Needed 18 pounds with a .8bar spring in order to open the valve substantially, pissed me off, thought I had been burned by the seller, contacted Tial, and was set straight. It works perfectly in the car.

[Alan L]

OK, exhaust pressure on valve face.
Many thanks.
I will road test and may end up putting old spring back in.
Weird thing tho, previously it tested on bench at 0.8 and opened on road 0.8.
Mechanical gizmos always keep a surprise for the unwary.
Regards
Alan

[PorscheGAL]

Originally Posted by RarlyL8

If you changed the diaphragm and the spring the only thing left is the valve and guide. At 100,000 miles it is likely coked up and sticking shut which would cause your problem.
How do you like the sound?

Brian, I love the exhaust. It has fundamentally changed my driving experience. I kept my stock exhaust, but I don't see why I would ever put it on my car again.

Originally Posted by cole930

PorscheGAL,

I'll give you $65.00 and shipping for your broken wastegate.

Cole

Not looking to sale the wastegate. Thanks for the offer.

[beepbeep]

If exhaust backpressure is lowered, it will take a weaker spring to sustain same boost as before. It's simple physics: gases take the path of least resistance. If going trough turbo is too hard, they will sneak trough wastegate. If backpressure after turbo is lessened, more gases will go trough turbo and less trough wastegate.

All that is "ceterus paribus", if wastegate is working correctly. If it's sticking or leaking trough the valve stem then it will have problems regulating the pressure.

[Alan L]

Greetings Goran.
Long time no hear.
Regards
Alan

[Alan L]

I tried two different w/gate systems and two different spring rates, and can confirm the w/gate opens about 0.1-0.2 bar lower when in car, compared to bench test.
I guess you have 1-2 psi pressure in the exhaust system working for you (at boost) - and probably varies from car to car.
Alan

[s5uewf]

Should my wastegate make a clunking/clinking metallic sound when it opens and closes? I tested today with it on the car with small amount of air pressure down the hose from the intercooler. I can hear small amount of air coming out the dump pipe - and when the wastegate opens it makes a metallic clink as it opens. Is this normal?

[Alan L]

No clunks.
It lifts off the valve seat when it opens. Perhaps a slight clunk on closing (reseating ) on valve seat. You could simulate this on the bench, or pull the dump tube off and do it in place under the car - hooking into the line at the w/gate body, and try and see what is happening.
Alan

[Alan L]

You will get a small amount of bleed past the valve stem (from under the diaphragm) as the boost pressure increases.
Cant be avoided in this imperfect design - but is minimal compared to the turbo capacity - but it is a small amount of boost leak which you will hear as a hiss as you pressurise.
Of course you will have other things to concentrate on at WOT and full boost normally and will not be bothered with such trivial boost losses.
Regards
Alan

[RarlyL8]

The metalic clank may be your stock BOV.