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Way TOO much boost

I was getting some irratic boost readings from my old boost gauge so I replaced it this week and found that the fluttering that I had seen before is gone, however the peak boost is pretty much consistent with the prior gauge. Testing it last night shows that the car can climb right up to 1.3B!

I am running a K27HFS, B&B Headers, stock WG spring and stock WG. Is this most likely just an iussue with the WG?

Thanks.
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Rob Montgomery
'88 Blk/Blk 930 ('Lucy') - Not Stock & Not Running
Old 04-19-2007, 05:32 AM
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How fast did it feel? How much boost were you running before?
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Old 04-19-2007, 05:49 AM
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It didn't feel scary fast once it crossed 1B. Maybe I am getting an artifical reading from the brake booster.

Its been overboosting for sometime. I have swapped between the stock WG to a TiAL with a variety of springs, back to a stock WG. All of this with and without a EBC.
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Rob Montgomery
'88 Blk/Blk 930 ('Lucy') - Not Stock & Not Running
Old 04-19-2007, 06:26 AM
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Are you using a 1Bar spring?

With my K27HF, I run a .7 bar spring and still get slightly over 1bar (in cold weather) - 1 bar in moderate/warm temps.

That's even with 1 3/4 pipe going to the wastegate from the GHL headers.

So if you run a 1 bar spring, I could see you hitting 1.3 bar... That'd be possible (assuming the B&B headers behave like the GHL's with the K27HF line of turbos)
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Old 04-19-2007, 06:37 AM
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I once had overboost issues. Valves hit pistons all that good stuff. There was a hairline crack in the WG housing. Couldn't been seen from crawling under there and just looking up at it.
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Old 04-19-2007, 06:40 AM
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Hi Rob,

Try removing your WG dump pipe. I had the same problem with my setup, and found that if I removed the pipe it reduced the the back pressure just enough to allow the WG to keep up with the exhaust flow. I'm not suggesting this as your long-term solution, but it can at least serve as a stop gap solution.

David
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Old 04-19-2007, 07:12 AM
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Thanks guys...

David... hope all is well. I actually pulled the dump pipe off for a brief period last weekend at the track and didn't see much of a difference. My problem is that the car likes to blow flame out the wastegate and if I don't have a pipe directing the flow of air... I'll likely end up with flames melting all sorts of stuff in the engine bay!

I actually just got off the phone with Stephen Kasper and I am going to re-plumb my TiAL and EBC on saturday with a really soft .5 B spring and see what that does. In theory that should eliminate any risk of overboosting past 1.0 B (or so I would hope).
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'88 Blk/Blk 930 ('Lucy') - Not Stock & Not Running
Old 04-19-2007, 07:33 AM
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Rob, I have .5 and .2 bar Tial springs if you need to borrow for experimentation.
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Old 04-19-2007, 08:22 AM
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Make sure the line from the Intercooler to the Tial is not kinked, and that the Tial is hooked up correctly. Ask me how I know.

I also have a .7 and .3 bar spring lying around, so if you want to experiment just let me know.

Bill
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Old 04-19-2007, 08:32 AM
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Yes, Stephen was the one who suggested I remove the dump pipe, but I wasn't shooting flames like you so I can see that that is not an option for you. My solution was a .65 bar boost spring and the removal of the dump pipe.

I'm hopeful that with all of the work that I'm doing to mine, that I won't end up with an overboost situation.

Regards,
David
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Old 04-19-2007, 11:41 AM
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Boost creep is caused by inefficient wastegate flow for the turbo setup/size.

I run a TiAL 46mm w/gate with a 1.0bar spring, on GSF 930 headers and I get absolutely ZERO boost creep when I turn off the EBC. My boost pins at 1.0bar all the time.
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Old 04-19-2007, 03:45 PM
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Merv -

At the risk of sounding uninformed... what are GSF headers? I think everyone has read about the ineffiencies of the B&B type design with respect to the waste gate. Would love to hear about some better alternatives.

Thanks
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Old 04-20-2007, 05:41 AM
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1. Wastegate shouldn't (and usually cannot) shoot flames. Flames are unburnt fuel that goes into headers while deccellerating or letting off throttle. When throttle is shut, wastegate is shut...thus nothing can go trough wastegate. I believe flames are coming off the exhaust pipe and not wastegate. It's sometimes hard to see as it's a very transient occurence.

2. Bigger turbo and more free-flowing headers exhaust means less back-pressure. With other words, bigger proportion of exhaust gasses will find it's way trough the turbocharger instead of being vented trough the wastegate. This is a common thing. Wastegate spring tension should be adjusted downwards (and in worst case, bigger wastegate installed) if you expirience boost peaks.

Easiest way to diagnose too small wastegate is to watch the boost vs. revs. If wastegate is able to hold certain boost at say, 3500 RPM but boost starts "creeping" upwards at higher revs (as more gases are produced) then it's time to go up one size.

If you just expirience boost peaks briefly just when letting off the accellerator, your BOV might be faulty.

If your boost peaks when you step on the accellerator just to go down later on (regardless of revs) then it's time to check for:

1. Binding wastegate valve stem
2. Wategate piping

If it doesn't help, go with less sping tension. If it doesn't help, install EBC (electronic boost controll).
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Old 04-20-2007, 08:38 AM
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I will see flames out the waste gate pipe. It all depends on how I transition through the gears. If the vid works below...the first flame is through the muffler, the second is through the waste gate pipe.

http://www.oz.net/~lyall/S4/Jeff%2091%20C2%20Turbo%20Flame%20shooting.MPG
Old 04-20-2007, 09:09 AM
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can't see a second flame, maybe its too small to see?
still doesnt make sense though, about flames from the WG, shouldn't/almost couldn't happen, and if it is think about what's happening to the diaphram
Old 04-20-2007, 01:09 PM
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If you shift fast enough the waste gate isn't closed very long. The fuel gets lit off just like going through the turbo. I've thrown bigger flames out the wastgate pipe then the muffler side at times.

The C2 turbo's have a different BOV configuration then the stock 930's which might help a bit. I also have the Forge valve instead of the stock. The Forge is supposed to be better at relieving the back pressure so as to not stall the turbo (can't say I noticed a difference over stock though). But rest assured...flames do come out the waste gate pipe!
Old 04-20-2007, 02:40 PM
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Here's another video....(me slowing down a friend). Passenger side is the muffler (custom Borla XR1) and the driver is a straight pipe off the wast gate (ie...stock wg muffler removed).

http://www.oz.net/~lyall/S4/Lyall%20chasing%20Jeff%2012-09-05%201.wmv
Old 04-20-2007, 02:46 PM
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cool vid. you can see it there for sure.
Old 04-21-2007, 04:22 AM
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Quote:
Originally posted by 930LDR
Merv -

At the risk of sounding uninformed... what are GSF headers? I think everyone has read about the ineffiencies of the B&B type design with respect to the waste gate. Would love to hear about some better alternatives.

Thanks
GSF= Going Super Fast brand, I think they are chinesse, good stuff thou.,Candy.
Old 04-21-2007, 04:41 AM
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Is exhaust pipe on the right and wastegate pipe on the left? In that case, fire is coming from wastegate as well...

It all depends on where you connect wastegate boost signal hose. If hose is connected to throttle body, there will be instant vacuum and wastegate will be kept shut on deccel, negating any flames.

If hose is connected to intercooler/pre throttle, sudden liftoff will make still spinning turbocharger try to pack air against closed throttle. Depending on size of turbocharger and BOV-valve, you might see a sudden boost peak pre-throttle until BOV evacuates the air, which might crack the wastegate open for a while and allow flames to escape trough the wastegate pipe.

Frankly, I don't find flames terribly amusing as they tend to heat up the exhaust and in worst case (Juan) set the rear skirt on fire.

If EFI is installed, flames are permanently "cured" by zeroing the fuel cells in the table where there is high vakuum and high revs. This is essentially a fuel cutoff, which makes engine draw zero fuel on decell. It will delete the flames, make engine more fuel-efficient and neutralize the popping sound on deccel when exhaust isn't hot enough to produce flames.

Some people like it that way, some don't. On CIS, there is a special deccel valve (brass disc with three pipes) which sole purpose is to neutralize excess fuel being dumped into engine on decell. Plugging this one will make even CIS car dumping flames.
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Old 04-21-2007, 06:11 AM
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