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Join Date: Dec 2006
Location: Germany
Posts: 401
Overboost problem solved

After receiving my new 88 targa I discovered a overboost problem very fast.
I do not like to push the engine in the overboost switch to often....
The 930 has a Ruf manual boost controler+ boost gauge.
Especially with the boost controler it took a while to find the main reason for the overboost.
Turning controler left/right, checking hoses, test driving...always I recognized boost above 1bar.
I disconnected the controler and tryed the WG connected direct.
No change at all...
I am happy that the boost switch came only onnce during all that

Yesterday I tested the wastegate with a pressure gauge+ air pressure at idle.
The wastegate opened only at 1.2-1.4 bar.
Without the engine running I discovered some blow by.
Seems the WG is bad....

As I had a spare Tial, I installed this quite fast, connected the Ruf controler,
test drive...problem solved.
I can dial now from 0.9 - 1.1 bar carefully, only using a third of the controler range.
Probably I need to install a softer WG spring to get better control.

...but now we have driving weather here, no need to work on the 930 all day.

Falk

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Old 05-05-2013, 02:30 AM
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How accurate do you think the stock boost gauge on the Tach is? On my car regularly hits or exceeds the 1.0 bar mark on a "spirited" acceleration. Car is supposedly stock, and appears that way externally.
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1986 930, Garnet Red Metallic
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63 904 (086), 63 904 (038)
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Old 05-06-2013, 08:04 AM
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Quote:
Originally Posted by Telerding View Post
How accurate do you think the stock boost gauge on the Tach is? On my car regularly hits or exceeds the 1.0 bar mark on a "spirited" acceleration. Car is supposedly stock, and appears that way externally.
I would say that electrical analog gauge in the tach is not very exact.
Further, I suspect on some cars it might read +- correct boost pressure,
on others not. On my 88 930 it reads more or less similar boost as
the mechanical boost gauge, but thats not a reference for all cars.

As said its electrical analog, what means the main electrical system
influences the readings a lot...alternator voltage etc.
Specialists here always recommend a mech. boost gauge to get accurate numbers.

Anyway, you can check your WG easy, as described above.
I have read here a few threats about wastegates, they are quiet informative
and most of them contain unfunctional WGs with a lot blow-by.

Falk
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Old 05-06-2013, 10:39 AM
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Location: Baltimore, MD, USA
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How much blowby did you see or hear in the stock wastegate when you pressure tested it?

I mean was it a loud woosh of air or a slight bleed off? Your overboost is probably coming from leakge past the valve stem assuming the diaphragm is not leaking.

Would be interested in getting feedback from you on how much clearance you find between the valve stem and the guide if you ever take the housing apart to fix it.

I have been looking for the spec on this clearance for awhile with no luck yet. In case I ever found a shop to make a replacement guide for a reasonable cost.

Thanks,
Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-06-2013, 12:21 PM
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Fred,

blowby:
Difficult to explain, but for sure not a big "woooshh",
it was more a slight bleed off, but feelable at the WG exit.

clearence:
The WG I took off from above car is still complete, but have a spare one which I could measure (all metric)
valve guide 10,19mm - valve stem 9,91mm= 0,28mm clearance---thats a lot!
Its a used one, but no visible wear on the guide or valve stem.

Had the chance to measure a Tial F46 too:
valve guide 10,01mm - valve stem 9,88mm= 0,13mm clearance ---thats not very thight too.

*Be assured the numbers are correct, we are used to measure those dimensions with calibrated tools.

Hope that helps

Falk
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87 930 bblk/blk
88 3.6 white/blk
Old 05-07-2013, 01:47 AM
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Join Date: Oct 2002
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Danke meine freunde.
Alles in ordnung.

Thanks for the information. Its interesting the Tial had less than half the clearance value. This is helpful information.

I was wondering if it were possible to run some sort of valve seal on top of the valve guide similar to an exhaust seal on the engine valves to eliminate the blowby inside the wastegate housing. I assume the temps are too high to have one last or Porsche and Tial would be doing it already. Its funny that seals last in the engine application on the exhaust valves but I guess the oil splash cools that area of the stem and guide alot more than the dry environment inside the wastegate housing.

Fred

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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 05-07-2013, 07:22 AM
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