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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Topic Review (Newest First)
06-06-2008 10:11 AM
wkndracr I would definitely say it's not the bpc because i get the same noise even when it is disconnected. it sounds just like when my old bov wasn't venting all the boost. I'm getting used to driving it so it doesn't happen, but it's a little annoying that i can't boost fully in 5th to pass someone unless i'm doing 80.
06-04-2008 01:33 PM
JZW The td04 would not be big enough. My 9k aero that I get the same thing you are describing is a tdo4 6cm2. I don't get any with my gt3076

I did get some with my gt3071 .64ar and my buddy had the gt2871 .64ar and he had it worse than me, but my head has been p/p.

My thoughts were that since my car was the best out of 3, Jak's, Co-saab's and mine, the p/p head was the reason. The lower in the rpm band you can make a lot of boost, the worse it will be on surge.

The hotter it gets, the worse the bpc boost chatter will be since its being controlled by pulses from the ecu controlling boost and the hotter it is, the more it will regulate boost.

The bpc is on the passenger side and that might be what you are hearing and not true compressor surge, which is louder and more pronounced...

John
06-01-2008 08:16 AM
wkndracr Ok, so i guess it is normal after all. I was thinking it had something to do with the motor not being able to take the extra air at lower rpm's and it's good to hear the same thing from others. I just figured there was some way to correct it. It does seem bad enough that the air comes back out the turbo, tho. I can hear it coming from the passenger side even with the bpv vented to atmosphere. I suppose with the warm weather now, it would be more prominent. I guess i just have to change my driving style to minimize it, or dig into the pockets to improve airflow When you say bigger turbo, do you mean just a TD04, or something even bigger?
05-31-2008 11:19 PM
Palmer Yep.


I pretty much figured out that this was my "issue" in my 9-3 with the GT30.


I heard some odd stuff under light boost at low RPM's and it freaked me out at first, but then I did some reading, and it made sense.
05-31-2008 11:15 PM
JZW
Quote:
Originally Posted by wkndracr View Post
10lbs was what Jak recommended, unless I'm remembering incorrectly.

Today I tried an mbc set to 15lbs for a couple of quick runs, and I get the same thing, although not as bad, as I get close to 15lbs. I'm wondering now if there's something up with the turbo.
Like I said, this is normal!!! every one I have driven in does it a little to a lot depending on weather and how low in the rpm you get on it... The head cannot handle the extra boost down low in the rpm... Once you reach the point where no more air can be pumped through the head, it backs up and pst, pst, pst out the bpc or bov and if it was really, really bad, it could back up and pass through the turbo compressor blades, true compressor surge...

I am sure Jak said try 10psi, but that does not mean 10psi is perfect for every car and 10psi is just a good ball-park. I had issues trying to run 10psi and 9psi, so just be carefull. Most run around 7psi....

All the stage 3's I have ridden in and driven here in Colorado have the same boost chatter that you speak of and its nothing to worry about in my opinion.

If you get a bigger turbo, it will no longer push as much air as low in the rpm and that boost chatter will be a thing of the past... Or P/P the head and that helps a good bit or just don't worry about it...

John
05-31-2008 02:07 PM
Legit Its not the turbo, it has to do with how the air is recirculated / vented either back into the system or the atmosphere.
05-31-2008 02:05 PM
wkndracr 10lbs was what Jak recommended, unless I'm remembering incorrectly.

Today I tried an mbc set to 15lbs for a couple of quick runs, and I get the same thing, although not as bad, as I get close to 15lbs. I'm wondering now if there's something up with the turbo.
05-31-2008 10:59 AM
JZW
Quote:
Originally Posted by lms View Post
Why are you running bb of 10psi and who recommends that?

I think 10psi is too high for you're set-up, the ecu cannot dump all the boost if the ecu detects knock. I had bad pinging at 9psi, had to lower to 7-8psi.

I would not run over 7-8psi!!!!

John
05-31-2008 05:58 AM
Legit
Quote:
Originally Posted by lms View Post
Why are you running bb of 10psi and who recommends that?
x2 just bring it down to 6.5
05-31-2008 05:23 AM
lms
Quote:
Originally Posted by wkndracr View Post
yeah, i just cranked up the base boost temporarily to see if that had any affect on it. It is reset to the recommended 10 psi. So is it more of a cylinder head thing, or would an upgraded intercooler and maybe 2.5" delivery pipe help the situation any?
Why are you running bb of 10psi and who recommends that?
05-31-2008 01:37 AM
Vigge
Quote:
Originally Posted by 93nut View Post
longer
shorter. If you increase the length of the rod you decrease the pretension = lower baseboost
05-30-2008 09:33 PM
93nut
Quote:
Originally Posted by jonny72888 View Post
quick question, to bring base boost up should you make arm longer or shorter?
longer (sorry, I meant shorter) hangs head in shame
05-30-2008 04:49 PM
jonny72888 quick question, to bring base boost up should you make arm longer or shorter?
05-30-2008 03:52 PM
wkndracr yeah, i just cranked up the base boost temporarily to see if that had any affect on it. It is reset to the recommended 10 psi. So is it more of a cylinder head thing, or would an upgraded intercooler and maybe 2.5" delivery pipe help the situation any?
05-30-2008 06:54 AM
JZW Yea, that is normal, you are pumping more air at low rpm than the head can handle.... ONce you get higher in the rpm its not a problem.

Putting base boost at 15psi is a very bad thing and can cause detonation and there is no way for the ecu to reduce or dump boost to save the engine.

I played around with base boost with my stage 3 and about 8psi was the max I could run without pinging. 9psi had some ping and detonation on the dyno...

John
05-30-2008 04:11 AM
wkndracr Thanks for the replies. I was thinking it may be the ecu controlling the boost, but it will happen with the hose to the wastgate actuator disconnected. the only time it doesn't happen is when i have the wg arm cranked so tight as to get like 15lbs of base boost, with the hoses to the bpc connected, but the electrical connector unplugged. I will try putting my old mbc back in temporarily and do a couple of runs to see if anything changes. It could be a warm weather thing i suppose, but i want to try everything before i write it off as normal.
05-29-2008 07:51 PM
codesplice ^^ That was going to be my suggestion, except I didn't know how to describe it as nicely as John did
05-29-2008 07:49 PM
JZW
Quote:
Originally Posted by wkndracr View Post
I have a 95 900se with a Jak Stoll Stage 3 setup including 3" turboback with cat , viggen i/c and tuned ecu. After ruining a couple turbo's due to a cheap blowoff valve (got the bosch one back in), I am experiencing compressor surge when I get above 15 psi or so and the rpm's are below about 3k. It's the same sound i would get between shifts when my old blowoff wasn't venting all the boost, but this time at peak boost levels, and I can hear it coming from the intake side. The aftermarket boost gauge I have also goes crazy when this happens. It will happen with the vacuum disconnected form the WG, but if i unplug the bpc and crank the WG actuator to make like 15lbs of base boost, it will creep to 20lbs with no flutter. I'm just noticing this phenomenon now since I reinstalled the turbo, but it may or may not have been happening all along before i replaced it. Any ideas?
I would have to hear it to be sure, but what I think you are hearing is the typical boost chatter or the pst, pst, pst of the ecu controlling boost! That is why you don't hear it if you leave the turbo unlimited with the waste-gate hose not attached.

That is fairly normal, you don't want it to run full boost all the time, that is letting you know knock is being detected and the ecu is dumping a little boost. This is normal ecu controlling the bpc and controlling boost...

I get the same thing, you are pumping more air than the head can handle at the lower rpm levels, try rolling into the throttle a little bit and go wot after 3k and the head will be able to handle the boost much better... I p/p my head for that reason and it all but went away after that, but my aero does exactly what you're car does at stage 3 level.

You will get varying amounts of the boost chatter depending on weather and the fuel you run...

If you don't want the tuned ecu to control boost, but a mbc on it and put the hammer down...

John
05-29-2008 05:33 PM
Legit Did you hook up the vacuum line to it? Also check your wastegate arm
05-29-2008 03:59 PM
wkndracr
compressor surge with stage 3

I have a 95 900se with a Jak Stoll Stage 3 setup including 3" turboback with cat , viggen i/c and tuned ecu. After ruining a couple turbo's due to a cheap blowoff valve (got the bosch one back in), I am experiencing compressor surge when I get above 15 psi or so and the rpm's are below about 3k. It's the same sound i would get between shifts when my old blowoff wasn't venting all the boost, but this time at peak boost levels, and I can hear it coming from the intake side. The aftermarket boost gauge I have also goes crazy when this happens. It will happen with the vacuum disconnected form the WG, but if i unplug the bpc and crank the WG actuator to make like 15lbs of base boost, it will creep to 20lbs with no flutter. I'm just noticing this phenomenon now since I reinstalled the turbo, but it may or may not have been happening all along before i replaced it. Any ideas?

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