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waste gate experts please

So as many of you know I"ve been chasing a lack of boost on my 86 turbo.. Finally got the waste gate off and figured I would run a test.. I pressurized the exit pipe ( tiny little muffler end) and while putting only minimal pressure on it, could see air ( with soapy water) leaking out the valve that goes directly to the exhaust. I'm assuming this is a valid test as under boost it would in my mind only get worse since the pressure would be pushing up on it and trying to open it up further.. Correct ?
So the plan will be get a new wastegate ( Tial ?? suggestions) and put that on the track dog, and move the other one over..

Am I correct in thinking that normally that valve should be tight as a drum and the seal must be shot ?

Todd

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Old 08-12-2008, 12:38 PM
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Tial would always be the way to go, but not sure if it would solve your problem. Isnt the boost gauge sensor further up on the system? If the gauge is showing your getting full boost, but your not, then it must be something else. If you believe your boost gauge is accurately showing you are not getting full boost, then it probably is the wastegate. did you also check the diaphram inside the WG? they are prone to cracking/disintegrating.
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1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
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Old 08-12-2008, 02:53 PM
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Wastegate doesn't need to seal perfectly. It does however need to open when you pressurize the diaphram (hose from IC). If that leaks the wastegate will not open.
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Old 08-12-2008, 03:00 PM
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I don't profess to be an expert, so I'll just share some learnings I've had and my own however flawed opinions.

If you're concerned about boost pressure being lost through a worn valve seat, or valve stem, I personally can't see how you would lose so much as to significantly affect boost to the engine. The turbos push a lot of air volume and it takes a much larger leak (like an intercooler o-ring) to substantially affect boost (just my opinion). The only way I could see that much boost being lost through the WG would be for the valve to be fully opening just as a result of the exhaust pressure upon it alone....as if you had an extremely weak spring in the WG with not enough tension to hold the valve closed against the relatively weak exhaust pressure. Then throw some boost pressure onto the diaphram and the valve would open prematurely. I know what I'm trying to say, but not doing a very good job explaining myself!

My guess is that there will always be some air escaping past the valve and guide, and probably more as time and wear/tear take their toll, but that should result in delayed opening, not the opposite.

At one time I didn't feel that my WG was opening up soon enough, causing overboost situations, and thought that it might be due to the boost pressure leaking past the guide. Bench testing had me putting in about 20 psi before the valve would open due to the leakage (I could hear the air escaping). So, I bought a used Tial 46 from someone (stated to be in excellent condition) with a .4bar spring. Initial bench testing had me cranking up the pressure to about .7 bar before it would open. Hmmm...I thought....this is not good. So, a quick technical question to the folks at Tial came back with the explaination that a certain amount of exhaust back-pressure was needed and that - in combination with the boost pressure - is how the springs are calibrated. The bottom line is that the boost pressure is augmented somewhat by the minimal exhaust pressure to help open the valve. In other words, bench testing alone won't tell you exactly at what boost pressure the valve will open. Long story short: I replaced the whimpy .4 spring with a .8, stuck the WG in the car, and it controls exactly to .8 waste. But I would be it would take considerably more pressure than that to open it on the bench only.

All this rambling is probably of little value in your issue. Usually WG issues show their ugly heads in the gate not opening at all (bad diaphram) or too late causing over boost. FWIW, and if I'm all wet I'm sure to hear about it!!!
Old 08-12-2008, 03:08 PM
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Some more info.. I tested the diaphram before and could hear the valve open and close with about the correct amount of pressure. My concern is that it does not close ever correctly. leaving it open and not allowing boost to build..
As far as boost guage goes I'm pretty sure it's reading accurately showing only about .4 bar boost if that and it's acting very sluggish as well.
Todd
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Old 08-12-2008, 04:04 PM
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If it's not closing completely then there's your boost problem. Is the valve stem sticking? I know those parts are pretty subject to corrosive gasses and heat.
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Old 08-12-2008, 04:30 PM
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Quote:
Originally Posted by AFM744 View Post
If it's not closing completely then there's your boost problem. Is the valve stem sticking? I know those parts are pretty subject to corrosive gasses and heat.
Well that's what I"m thinking, was just doing a sanity check.. I put MINIMUM pressure back into the sytem from the overboost escape muffler and could blow bubbles through the valve ( soapy water on it).
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Old 08-12-2008, 04:42 PM
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OK , so here's the pic after I took of the mini muffler.. I don't think there's suppose to be THAT much air around the valve is there?? LOL
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Old 08-12-2008, 06:49 PM
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Wastegate valve must be very leaky in order to significantly affect boost. I'm not sur that little leak on picture is enough.

I believe your main problem is leak somewhere between engine and turbo. Intercooler O-rings, phenolic intake spacers etc.
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Old 08-13-2008, 01:24 AM
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Quote:
Originally Posted by beepbeep View Post
Wastegate valve must be very leaky in order to significantly affect boost. I'm not sur that little leak on picture is enough.

I believe your main problem is leak somewhere between engine and turbo. Intercooler O-rings, phenolic intake spacers etc.
That's a pretty big leak, I can see light around the whole valve! I would think that there would at least be some resistance when I back blew some air in there..
T
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Old 08-13-2008, 05:27 AM
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Why not test the WG by blocking off the muffler outlets with a rag and see how much leaks through the WG. Mine leaked nothing at idle. I bought a Tial anyway
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Old 08-13-2008, 10:46 AM
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Quote:
Originally Posted by 9dreizig View Post
That's a pretty big leak, I can see light around the whole valve! I would think that there would at least be some resistance when I back blew some air in there..
T
OK Todd, I'm with you on that. Light showing through is not a good thing. I presume at some point you have completely disassembled the WG, valve and all? My guess would be either a bent valve stem, seriously corroded/carboned-up guide, or warped valve seat. Take it appart if you haven't already, clean out the guide and stem, get some valve grinding compound and hand-lap the valve seat. If none of that helps, then it's shot. Something is sticking somewhere, even with all that spring pressure it still won't fully seat. There was a post awhile back on Rennlist that dealt with having a machinist make a new guide. That's an option for you.

Finally, here's one more thing to think about...the recirculation valve assembly may be defective. If the piston is stuck in the up position, you won't build any or very little boost at all. Here's a cut-and-paste from a description I gave awhile back:
--------------------------------------------------------------------------------

"The recirculation valve basically takes the place of a blow off valve in later model turbo engines. Essentially what it does is to redirect the pressurized air from the intercooler/engine intake manifold, back to the front intake end of the turbo. This takes place under sudden change in engine vacuum (as in when you lift your foot off the throttle to shift). The sudden increase in vaccum is transmitted via a small hose to the piston assembly, causing the piston to rise and uncover a port to redirect the pressurized air. This balances the pressure between the intake and outflow ends of the turbin, allowing it to freewheel. This, as opposed to the high pressures residing post-turbo with no place to go when you lift your foot off the pedal. The air pressure would otherwise have to travel backwards through the turbo - causing it to slow down dramatically, put undue wear-and-tear on the turbo, and create a huge turbo lag when you put your foot back on the go pedal."
Old 08-13-2008, 12:50 PM
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Why not just pull the wastegate off of the '80, install it on the '86 and go for a drive?

That ought to answer the question pretty quickly.

JR
Old 08-13-2008, 02:32 PM
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Quote:
Originally Posted by javadog View Post
Why not just pull the wastegate off of the '80, install it on the '86 and go for a drive?

That ought to answer the question pretty quickly.

JR
That's the game plan, first thing Sat afternoon when I get back home....
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Old 08-13-2008, 03:28 PM
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When running the car do you feel alot of exhaust coming thru the wastegate muffler at idle?
You could take the little WG muffler off and reinstall the wastegate to see how much exhaust is leaving thru the open port in the wastegate.
It would have to be a substantial amount of leak to effect not reaching max boost because the turbo should have enuff capacity to hit full boost even with a substantial leak from the wastegate.
Likely you have problems in the intake portion of the car where your loosing boost pressure or the gage is faulty/inaccurate.
What boost gage are you basing these numbers on?
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Old 08-13-2008, 04:22 PM
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I would say just don't plink down a load of dollars on a Tial when the OEM WG is a fine piece.....find out how much to rebuild it first.
I like the OEM unit as it is thermally massive (lots of heat rejection) and well designed. Though replacement parts and springs are not as interchangeable as Tial sounds.
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Old 08-13-2008, 04:26 PM
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Fred,
I"m basing it on two things a) it's running like a dog b) the speedo boost guage,, yeah I know it's not accurate, but remember I have another car to judge it on, and this one is just not getting it.. so I"m sure it's not the guage,, plus it has slowly degraded over the last few months
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Old 08-13-2008, 04:30 PM
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Only way to know for sure is go thru the entire system iece by piece. The exhaust needs to be checked. Then move on to the intake side as there are more chances for leaks in that system. Lots of o-rings in the intercooler plumbing and all those vacuum hoses. The fact that it degraded over time means something is definitely off, I agree.
Don't want to harp but the greatest thing I did was buy the VDO boost gage that goes in place of the clock. You will be amazed at the inaccuracy of the tach gage when you see that new gage working. Plus it is lots easier to read.
Good luck.
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Old 08-14-2008, 03:46 PM
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well took the good wastegate off the track dog and no luck !! it ran the same,, still only pulling .4 bar... so am putting the old one back on. Not sure where to go next.. I think I'll try Allans approach going to pressurize the system and see where the vacuum leak is..
My question is how do I know if it's in the diverter valve ??
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Old 08-16-2008, 05:50 PM
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Did you try blocking off the muffler first?

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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 08-17-2008, 01:01 AM
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