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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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Old 02-20-2013, 01:11 PM   #1
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Surge Likely on T28?

I've been spending some more time in the car lately, and for a brief period, I ran a helper spring on the wastegate. I stopped because when at 60%< throttle in third, around 25-700rpm, it would boost to ~22psi and then make the unmistakable "shhhhhchchchchchchchchc" of compressor surge (I think). If you don't know what that sounds like, look up a youtube video of "real compressor surge".
I removed the spring, and have resumed running just OE wastegate load and the T7 BPV valve. It still does it though, and still boosts pretty hard and early. However, I do not remember--ever-- a time when it did that. The BPV moves freely, and blows off, around idle with a slight blip. The T7 valve also clicks away merrily. So, from the maps I've seen, it doesn't seem likely that I'd surge the turbo at this pressure ratio/flow. The only thing that has changed is that my intake manifold holds pressure a little better than it used to and the tune has gotten better with regard to fuel and ignition. I've seen a lot of tunes with this same or similar turbo's and they run right up to 30 psi with no surge. Weird thing is that it seems to make plenty of boost (~25psi) in 4th, with no surge...that I can hear. What gives!
-Cm
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Old 02-21-2013, 12:58 AM   #2
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I seem to run 28lb pretty good. And I run a thick bed spring (helper).

Maybe the noise is your turbo at full song.

Real compressor surge is a pretty nasty sound.
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Old 02-21-2013, 04:40 AM   #3
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I'm also running a helper spring which creates 10 psi base boost. This is recommended by JZW for his T28 Stage 5 tune. I don't notice any surge in my setup.
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Old 02-21-2013, 05:19 PM   #4
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https://www.youtube.com/watch?v=nCj6Spwl1CU
This...around 48 seconds.Not the high pitched business and stuttering, but that "tcchhhhtccchhhtcchhh" sound. It used[ to not do this...The turbo has only 5k on it. I run an open air/cold-air intake...maybe it sucked something up? Salt Over break I ran the spring on it and it would hold 25psi all the way to the end of the revs, but it didn't run "well". Afr was fine and it knocked here and there. I took the boost down and it ran better. I never took it past 30 or so psi, so I can't imagine I broke anything turbo wise...
-Cm
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Old 02-22-2013, 01:46 PM   #5
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Might it be that the stroke on the wastegate actuator is too short because of pre-load? It only opens about 30 degrees, or linearly, about 3/8-1/2". Which is strange, because I haven't adjusted the wastegate since prior "optimal" operation. Should I just back out the wastegate and then run the helper again?
-Cm
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Old 02-22-2013, 03:43 PM   #6
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Yep, Put the wastgate adjustment back to where it was (standard).
Get a 2mm thick helper spring.

Use the wastegate adjustment to "fine tune" your base boost, up or down a pound or two.

Edit:

Ive been thinking of knocking my base boost back abit so I spike at 26 -27lb. I think the 28lb I spike at now might be a little high.
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Last edited by bogan; 02-22-2013 at 08:51 PM.
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Old 02-25-2013, 11:23 AM   #7
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Perhaps...I dunno. David ran 'em balls-out and purportedly hasn't run into any trouble. I switched DIC's and the problem has alarmingly seemingly vanished. I think I fried my now "troubled" DIC on those shorter BCR8's. Currently I'm running my ancient spare. Anyway, this is why I have these sometimes neurotic posts--the strangest things cause seemingly unrelated problems. Another example is how I spent months and a lot of money tracking down an EVAP problem, where the tank was getting sucked to the point of collapse. After part throwing my ass off, someone just happened to come across my threads and posited that the tune, though ostensibly the same, might be a eurospec and thus incapable of driving US EVAP systems. It worked.
-Cm
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Old 02-26-2013, 12:39 AM   #8
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I'm going to back my boost off a bit. I think the 28lb I'm spiking at is too much.
I'm going to get it spiking at 26lb.

I think I have heard my turbo surgeing under boost a couple of times too , come to think of it. :-/

I'm playing with my base boost this weekend.

I got a track day coming up. I got to get this fucker to sing
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Old 02-26-2013, 07:40 AM   #9
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Quote:
Originally Posted by bogan View Post
I'm going to back my boost off a bit. I think the 28lb I'm spiking at is too much.
I'm going to get it spiking at 26lb.

I think I have heard my turbo surgeing under boost a couple of times too , come to think of it. :-/

I'm playing with my base boost this weekend.

I got a track day coming up. I got to get this fucker to sing
FWIW, I've turned it down to a lower spike as well--seems to run as well if not better and is certainly easier on the turbo. I forget; are you running the T7 valve? If so, then the high spikes and heavy wastegate pre-load don't seem to be necessary...
Good luck at track day, although, your LSD + T28 are going to make for some interesting wash-outs.
-Cm
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Old 02-26-2013, 10:28 AM   #10
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Years ago when I installed an 18t in my viggen with a road tune I decided to get all tricky and shit with the waste gate arm. All this did was cause issues in drivability. I'm not sure even why I did it, I guess I thought that turning the rod/using springs would be just like the days of my spg, NOT! Went back to where BB was set when it was road tuned and never looked back. I spike at 22 and it holds steady until I let off with a BB of 7. If I go higher then all sorts of shit starts to happen. The little 18t can only muster so much oomph and pushing the limit just causes issues. I think the same holds true for a lot of small/mid-range turbos, but I’m not a home tuner.
I also used to get surge out of my spg when I went to a T3 super 60, why, because I started f-ing with te damn wastegate, once I dialed it back, happy car.
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Old 02-27-2013, 01:23 AM   #11
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I think your right bruv ^^

"Less is more"

I also tell that to the ladies
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