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epsylon

i removed my old turbo for a rebuild and installed one that i had rebuilt a while ago along with a uncracked exhaust manifold. the car runs great and sounds so much better but now my boost reads about 7 psi instead of the 9 or so it was reading before. any ideas?

i thought the boost level was controlled by the wastegate alone. could the other turbo somehow have built more boost???? or did i fix some hidden problem when reinstalling everything. i did have a nasty exhaust leak but i thought that would have robbed me of boost.
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'82 931
'78 928
Howell Henderson
South Padre Island

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

As has been noted before, the K26 can be assembled from components that give the entire assembly different performance characteristics. I don't know if one of those characteristics is a higher level of compressor output per #turbine RPMs. Here's a thread with the most definitive information about the K26 that I've found anywhere - as far as it relates to Porsche and KKK part numbers.
http://www.924board.org/viewtopic.php?t=10928
It'd be nice to know/share info if you could post any/all data plate and/or casting numbers from either/both your units. Perhaps over time we (collectively) could "decode" all the various ways the components were (or can be) mixed and matched.
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'79 Eurospec 931

epsylon · Posted: Wed May 19, 2004 3:49 am Post subject:

good read. i will post the turbo numbers when i get home. i actually have a third turbo, but i have never run it on the car so i don't know how it performs. strange though, why would my wastegate/system allow the other turbo ( old one ) to spoil up to 9 psi and not allow this turbo to do the same just at a different/higher RPM? this turbo is caping at 7 psi. it reaches 7 psi and stops well before i am into the higher RPMs.
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'82 931
'78 928
Howell Henderson
South Padre Island

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

?? Maybe it is only putting out 7psi all together. I'm just "reaching" here, but the wastegate could be opening at 9, or it could not be opening at all, and the first turbo only put out 9 ?? It would explain it, but I don't know how valid an argument it is.
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'79 Eurospec 931

epsylon · Posted: Wed May 19, 2004 4:16 am Post subject:

these turbos are capable of puting out a lot more than 7 or 9 psi. i have heard of people running in excess of 20 psi with the stock turbos. unless the rebuilt turbo is bunk which i would expect other problems then just a boost cap. isn't there some sort of built in BOV in these units? maybe that is causing the 7 psi boost cap.
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'82 931
'78 928
Howell Henderson
South Padre Island

Smoothie · Posted: Wed May 19, 2004 6:54 am Post subject:

Someone (I think it was Paul) wound up with a rebuilt turbo that had its' pop-off valve reassembled backwards. The result was boost limited to something like 4 psi. 7 psi is close to normal though, so I wouldn't expect yours to have the same problem. No idea why you'd have been getting 9 psi previously. Any chance there was a leak in the wastegate control line that got fixed? Exactly where was the exhaust leak?

Or - how about this scenario?.. Your gauge is reading high by 3psi, so your old turbo was actually making 6psi and your new one is making 4psi due to a backwards pop-off valve...?
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Paul · Posted: Wed May 19, 2004 10:45 am Post subject:

Yep, it was me, and it was the reason I first joined this board!

If you're having the same problem:

the waste gate never opens
oil on the J pipe never burns off
you will hear no clicking noise as you blip the throttle
unhooking and plugging the waste gate control line has no effect
your 0 to 60 times will be more than 10 seconds.

epsylon · Posted: Wed May 19, 2004 11:50 pm Post subject:

i think smoothie might have nailed it. i did replace the wastegate line because i could not nail down a raspy vacuum leak type sound in that area so i just replaced all hoses and lines around there when i had the turbo out. the sound is gone, i just assumed it was one of those little rubber elbows, and now i am running 7 psi which is factory for some US cars so it must have been the line.

paul, thank god i am not experiencing those symptoms.
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'82 931
'78 928
Howell Henderson
South Padre Island

numbbers · Posted: Thu May 20, 2004 9:10 am Post subject:

Ok, now that you know that your car runs fine with 9psi, is it time for a variable boost controller?
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1980 924 Turbo

epsylon · Posted: Fri May 21, 2004 4:16 am Post subject:

exactly my thoughts. i am going to get me one of these, http://www.boostsciences.com/reliaboost2.html , thanks for the link nick.

i figure most US spec'd 931s could handle 9 psi without trouble, unless the engine is tired.

although i should check to make sure the fuel mixture is correct at higher boosts, don't want a lean condition.
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'82 931
'78 928
Howell Henderson
South Padre Island

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

FYI- they have a new one now that looks much easier to adjust (no tools required). It's on their website for ~$10 more or so. Remember to pick up some 3/8" to 1/4" barbed adapters to plumb it in. The wastegate line is 3/8.

Enjoy!
-nick