compressor surge, what does it feel like?

[ghostcar]

at the track last week i turned up the boost from 18 to 22 and noticed that at WOT at the middle of fourth im getting a chuh chuh chuh sound about twice a second. like the bov is half assed blowing off rapidly. im almost positive this is compressor surge (after searching here) and the car has a very soft pulsing hesitation (compared to bad plugs or fuel cut) at the same time.
the turbo is a presicion t4 57trim (the exact model eludes me im at work currently) with a fairly large turbine housing with a 3 inch v-band outlet.
the motor is an internally stock cyclone motor
2.5 ic pipes

the rest of the time the car is fine, idle, 2nd, 3rd, boost is practially non-existant in first though but i kinda expect that.

what do you think, am i on the right track?

 

[m_0ney_pit]

If you are running the greddy s or rs try doing the single spring mod, isn't that boost level to much for the fuel system?

 

[gsxeclipse97]

it could be if your running a stock clutch that it was trying to catch since you don't have one listed im going to assume its stock. That may be to much power you are making.

 

[ArticNemesis]

It's not compressor surge. Compressor surge happens between shifts, or backin off the throttle, allowing the plate to close, causing the compressed air from the turbo to stop extremely rapidly. The blow off valve remedies this situation.

It sounds more like a premature opening of the blow off valve.

 

[ghostcar]

to answer a few of the comments. its a stock uncrushed 1g bov.
the clutch is stock, but this is not a dsm, its in a very much lighter car. also the engine wasnt revving up, i would think the clutch would have more of a tendancy to slip while launching at 6000 rpm with 25x8.7 slicks.
the boost gauge was pulsing back and forth between 20-24 psi during this "noise." i really wish i could explain it better, it sounds like the turbo is spooling then slows down and then starts back up in quick succession

http://www.turbominivan.com/tech/turbo201.htm
according to this website surge is " Surge is the situation when the compressor "spits out" more air than the engine can swallow, which causes a backup of air at the intake and it actually creates reverse-flowing pressure waves that can be very damaging to the turbo."
also i've pressure tested the sytem to 25 psi with no premature opening of the bov or boost leaks. and my bov works normally under all other conditions. this is happening at WOT. if it matters i was on a 50/50 mix of 91 and 110 octane and had 4 counts or less of knock during the pass. (it was the first time upping the boost so i hadnt finished the tune of the top end all the way but have since eliminated the knock but not the surge, or whatever it is

 

[spinz4]

Compressor surge happens when you let off of the throttle.....And only your turbo will feel it.

 

[ArticNemesis]

That's the point of forced induction, you are forcing air into cylinder chambers.

When you overcome the limits of the motor to adequately create a combustion the air/fuel mixture, you get knock, not compressor surge.

I just don't see a turbo at 18-24psi flowing more air than an engine can handle.

 

[ricktb]

Heres a vid I found that might help... the part about compressor surge is at 0:30 seconds..

http://youtube.com/watch?v=MU5Y6d9rh1k