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turbo pressure (930- 3.3)

Hello porsche expert. I have discovered my turbo pressure is 1.1 bar at max and engine runs incredibly well. Engine may be damaged or should I go back to 0.8 bar

Regards john
Old 05-23-2010, 12:39 PM
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Enthusiast here. Standard answer is to verify your AFR's are in spec, you use the highest octane fuel you can find at the pump, timing is conservative, and that you have a large intercooler. Even at that 1.0bar is the standard that is not passed for most applications. The stock overboost switch should kick on at 1.1-1.2bar so you might check that it has not been disabled.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 05-23-2010, 01:33 PM
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My intercooler is standard and overboost switch kick on therefore wire mounted on the frame (-) but the engine has just been renovated, 30,000 so it surprised me.
Old 05-23-2010, 02:00 PM
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No you should not be running over stock boost w s stock inter cooler.

Why are you boosting so high?

1 bar spring, quick spool turbo, ...?

What mods do you have?

How do you know you are boosting so high?

Last edited by 911st; 05-23-2010 at 05:25 PM..
Old 05-23-2010, 05:22 PM
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Hello. the previous owner has installed 1,0 bar wastegate boost spring ,but I can look at VDO turbo boost gauge 1,1 bar ,how can this be done? and overboost switches off fuel pump? it should do after the first 1.2 bar. weird
my turbo is original k26 and the engine is also original with b&b Headers & Muffler
Regards john
Old 05-24-2010, 09:32 AM
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The B&B's tend to boost high. Had the same issue. It seems to be because of the less than ideal waste gate circuit.
Old 05-24-2010, 03:18 PM
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Get a stock spring unill you get a better IC. A K27-7200 of other more efficent turbo w stock boost will run probably as well or better.
Old 05-24-2010, 03:25 PM
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The B&B's tend to boost high. Had the same issue. It seems to be because of the less than ideal waste gate circuit.
Seriously retarded timing can cause overboost.
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Old 05-24-2010, 06:19 PM
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interesting.

Are you talking 'anti lag' retrard with a lot of extra fuel or just a locked mechanical advance retard?
Old 05-24-2010, 07:35 PM
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what can happen if I continue to run at 1.1 bar ??
Old 05-25-2010, 12:52 AM
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The biggest concern is that right now you do not know if 1.1bar is safe for your engine. Under normal circumstances 1.1bar with a stock intercooler will shorten your engine's life. Detonation is an issue.
IF you live in a cool climate AND your timing and fuel are spot on AND you run high octane fuel AND your intercooler does not get into heat soak THEN this high boost level may not be harmful.
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Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-25-2010, 05:01 AM
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Quote:
Originally Posted by jeos View Post
Hello porsche expert. I have discovered my turbo pressure is 1.1 bar at max and engine runs incredibly well. Engine may be damaged or should I go back to 0.8 bar

Regards john
I think possibly the best thing to do is to get the car on a Dyno (shouldn't cost too much) and get a log of your AFRs and Boost Pressures against RPM.

Yes, use high-octane fuel if you can get it.

Racing Porsche 935s used to run at around 1.4Bar - but their engines only had to get to the end of the race. Generally accepted that 1.0Bar should be okay, but much more than that and you are going to shorten the life span.
Old 05-25-2010, 05:13 AM
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1 bar is not acceptable w a stock IC. Especially w a stock inefficent turbo. That is to much heat for what is in effect 11/1 CR.
Old 05-25-2010, 07:01 AM
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Quote:
Originally Posted by 911st View Post
interesting.

Are you talking 'anti lag' retard with a lot of extra fuel or just a locked mechanical advance retard?
911st.......

From my experience a few years ago I had a 930 that would boost to 1.1 under load and would spike to 1.3 with a readable boost gauge , between shift. Opon inspection, with the distributer turned to full advance as far as could be advanced on the slide, it was only around 20 BTDC @ 4000 RPM. The factory manual says 27degrees BTDC for US and 29 BTDC for Euro @ 4000RPM. I pulled the distributer and turned it back a tooth to get the sliding mechanism in the center of the travel. Set it to factory setting @ 4000 and the boost settled to 1.0 bar under load and no more spiking, which upon inspection was the waste gate spring specification.

JEOS...........My recommendations would be the same as most others. If timing is set correctly to factory spec and boost is still being measured accurately above 1 bar (with a 1 bar spring the boost should be 1 bar ) so something is wrong elsewhere. Even @ 1 bar you should at least have a larger intercooler, more fuel enrichment and 110 octane fuel with low outside temps to stay on the gas pedal but for short runs, otherwise you will indeed be in touch with a motor builder soon.
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Last edited by voitureltd; 05-25-2010 at 08:29 AM..
Old 05-25-2010, 07:40 AM
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I'll try to look at the timing then we see if it helps. thanks for all your answers

Regards john
Old 05-25-2010, 09:45 AM
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Tony, Got it.

With CIS a lot of fuel can still get pumped if the metering plate is slow to respond and a fair amount of fuel can make it to the exhaust.

The dist also retards about 10 deg with manifold vacuum (net -10 in the case your described). With these two things it could be fuel was still burning when the exhaust valves opened and there was so much expantion in the exhaust system the WG could not vent it and it effectively overboosted.

Or the raw fuel might have just made it the the hot turbine wheel and turned it into a little jet motor for a bit.

Also sounds like the BOV was sticking or to small.
Old 05-25-2010, 05:09 PM
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hello again. I have now checked timing and it is fine. I've been told that there are sims in wastegate bell as one can take away to lower pressure. is it true??
Old 05-26-2010, 04:17 AM
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Unless it was the last owner that told you that, it is unlikely. Most advise against shims on a Porsche WG.

Again, B&B plus one bar spring equals 1.1 bar boost.

Over about .8 to .9 boost plus a stock intercooler equals high potental for dammage.

Put a stock .8 bar spring in and you should be near .9 bar.

Gone.
Old 05-26-2010, 07:39 AM
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how much power is removed if I go down to o.9 from 1.1 bar
so about?
Old 05-26-2010, 08:57 AM
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Quote:
Originally Posted by jeos View Post
how much power is removed if I go down to o.9 from 1.1 bar
so about?
Not sure on the power drop from that change, but as others have said, if you continue at 1.1+ bar with your current build, you will likely soon lose ALL power !!!
Old 05-26-2010, 09:23 AM
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