toddk911

Would it be possible to loose the 3 psi if my stock down pipe collapsed???

Jason_86_951

Yup!
Pull your cat bypass and have a look.

Porsche-O-Phile

I've been told that the down pipe and the one that connects that to the catylitic converter are both double-walled and can potentially experience an internal collapse without being visible from the outside.

I'm a bit suspicious of the wastegate on my car, but until I can replace the siezed-up a/c compressor pulley (probably next weekend) and get it running again, I won't really be able to test it. IIRC the way to test is to start the engine cold and immediately feel for heat at the wastegate dump pipe. I'm assuming this is the one that goes straight to the back of the car (duh) although I'm trying to understand the logic of the test:

In theory, would the car divert all flow out the back at idle or is there a signal sent to the wastegate in order to close it and divert flow to the turbocharger in order to keep it spooled (seems to make sense, but hopefully someone can confirm this). It also seems to make sense from an emissions standpoint, since one of the worst things from a pollution standpoint that can be done is to sit idling the engine. If the wastegate is closed at idle, sending all flow to the turbocharger, that means all flow goes to the catylitic converter, maximizing efficiency at idle.

Is this really what is supposed to go on?

Jason_86_951

In a nutshell, yes.
The purpose of that test is to see if the WG is closing all the way when it should (not stuck open).

turbite

Where are you tapping your boost control again?

UK952

The standard wastegate should hold itself closed, sending all the exhaust through the turbo, the signal (boost) comes later and tells it to open diverting some (most) of the exhaust gas straight to the rear of the car and preventing too much boost being generated and blowing the engine.

With a weak spring or damaged wasegate valve the exhaust will leak of the wastegate down the pipe to the rear instead of making its way to the turbo.

I imagine if the pipe from the turbo is collapsed this will generate a flow restriction increaseing the pressure on the wastegate valve which will force it open early (loosing you boost).

With a dual port wastegate the boost signal can be applied to both sides of the wastegate to hold it closed or to force it open.

I drew a picture here to show roughly how shimming works that might help make it clearer

Tony

toddk911

"I imagine if the pipe from the turbo is collapsed this will generate a flow restriction increaseing the pressure on the wastegate valve which will force it open early (loosing you boost)."

I see how this would decrease boost levels, but if this was the case, then turning of the boost controler would give more boost. Yes, the turbo would be spinning much more to generate it, but it would still make more boost.

In my case, I can keep turning up the boost controller (reliaboost) and still only get and hold 15psi. And disconnneting the wastegate complelty and only geting 15psi. An dthat is only in 3rd and 4th gear. Where as before I would get full boost in everygear except 1st.

This all happened like 3 days after installing my new DV, but I put the old unit back in just top check and still only made the 15psi.

UK952

If the exhaust pressure is forcing the wastegate open I dont think you will get the turbo to spin any faster. The reliaboost wont make any difference if the wastegate is being forced open early - it is out of the loop, the boost never gets to the point where the reliabost will open. You have confirmed that by removing the signal line.
Tony

Danno

Todd, you might be following in the steps of several Rennlisters:

- Jason_86_951
- eclou
- Timm Baldauf (K26/8)
- jake951 (K26/8)

They all had low/dropping boost problems with shimmed wastegate. Some of them tried the Tial wastegate, others the GURU, then the Tial. In all cases, their boost-problem didn't improve and the turbo was the culprit and was replaced. One guy actually blew up his turbo, snapped the axle & compressor-wheel to bits when he tried adjusting the boost-controller to get more boost.

At this point, since you already have an upgraded wastegate (the very first GURU wastegate actually), I don't suspect it's at fault. We have a couple options to look at after a final test:

TEST: remove control line from wastegate completely, then go several full-rev runs. Start at 50% throttle and go to 6000rpm. THen 75% throttle, and see what the boost is. Should hit max-boost by 3500rpm with 75% throttle. If not, do another 75% throttle run and gradually increase throttle to 100% after 3000rpm if boost doesn't hit 18psi.

After this test, and if you have insufficient boost, we can rule out the boost-controller as being a culprit and look at some other areas:

- wastegate: I can send you a newer GURU wastegate with 1.0-bar spring to replace your 0.75-bar unit, but that most likely isn't it because I'm running 25psi on the 0.75-bar wastegate now.

- exhaust: You might have a collapsed inner wall in your exhaust section just after the down-pipe. This pipe wraps underneath the car and often gets crimped by coming down onto speed-bumps too quickly. The inner pipe also collapses due to differential expansion rates between the inner & outer walls. You can test this by removing all exhausts after the down-pipe and redo that 75% throttle test again (it'll be loud!)

- turbo: this is the final culprit. I had one car with a bent axle that couldn't generate boost. Another had broken turbine blades due to an exhaust nut being left in the headers by the engine-builder. Not sure of any way to test the turbo other than to replace it. You can pull the intake-boot and spin the axle by hand to see if it's binding anywhere. Also measure the axial & radial free-play.

Porsche-O-Phile

I just got done reading on the Clark's site that the amount of boost required to "force" open the wastegate spring is roughly 1.2 bar - exactly the amount I'm getting. This would normally make me suspicious of the "signal" coming from the cycling valve to the wastegate, but the problem with that is, I get the same result with the line to the wastegate disconnected. In this case, it seems that the wastegate should default fully closed and I certainly should get boost. I don't. If the wastegate were sticking, I'd have a partial signal going to the turbo and most of the exhaust going out the back as bypass or "dump" air - very little going to the turbo.

I'm just wondering about the coincidence of the amount of boost I get - 1.1 to 1.2 bar and the Clark's write-up mentioning 1.2 bar as exactly the amount of boost I'd get in the event of a cycling valve failure. But then why does the problem persist with the cycling valve out of the loop? Hmmm. Strange, but it seems it must be coincidence and there must be something mechanical (i.e. wastegate) amiss. If I check mine and it's stuck, I guess I'll be going with the GURU one.

UK952

If the cycling valve failed so that it was sending the signal to open the wastegate early, the wastegate would open limiting your boost.
If your wastegate is stuck open or leaking it would also limit the boost in the same way.
You would end up with the same level of boost either way.
In your case (P-O-P) removing the line from the cycling valve made no difference so it wasn't the cycling valve causing the problem.
Ordinarily with everything working and the standard chips the signal (to open the wastegate) wouldnt come from the cyling valve until you were near to maximum boost. You are not achieving this level so the cyling valve isn't trying to open the wastegate so disconnecting it makes no difference.

Note:- Remember that 1.2 bar on the standard guage is only 0.2bar of boost (1 atmospheric pressure + the boost).

Tony

special tool

okay, wait a minute. Danno says you have a guru dual port already, so that narrows it down even more. You probably have a worn out turbo, man.

Also - if I was you, I would rely more on the advise from guys here, because I don't think you understand the mechanics of the 951 well enough to be reading clarks - it is just confusing you.

UK952

Todd has the guru wastegate, Posche-O-Phile has just fitted a replacement turbo - I been spending too much time reading rennlist this week, time to go for a drive!
Tony

Porsche-O-Phile

Yes, this one's certainly a puzzle. I'll (hopefully) be replacing the siezed a/c compressor pulley soon at which point I'll have a functioning car to troubleshoot turbo issues on.

I'm pretty sure I need to replace the cycle valve anyway. The plastic nipple onto which the line to the wastegate connects was snapped off and kind of "shoved" into the orifice in the side of it. I'm probably not explaing it very well, but I observed this with a mirror and tried using some sealant to hold it in place. It looked like a decent enough repair, but it's still not the problem. I figure the only way to be sure is to just start replacing stuff - I replaced the turbo already, so I'm pretty sure that isn't the problem. The cycle valve I'll replace soon and I'll also check the wastegate whenever I can put my silver car (the one that's going to be the Callaway car) back together off the jackstands and out of the garage - I'm sick of doing these repairs in the street - I ain't doing it anymore!

UK952

You will end up binning the cyling valve when you start uprating so dont worry too much about it,
Tony