Help w/compressor surge @10p.s.i.

[yellow_jacket]

Originally, I though it was the bov leaking at that pressure. So of course I ripped it out and replaced it. Only problem is now it still does it. The motor appears to be completely stock. No mods. Stock i/c, turbo, piping, intake, cams, etc etc.

Any great ideas to fix this?

This is NOT between shifts, this is running wide open.

[rudee023]

Not quite clear there. It still does what? Leaks or surges?

[yellow_jacket]

still has compressor surge.

[s13sr20chris]

what are you using for boost control?

[yellow_jacket]

AVC-R

[RMiller]

What does boost control have to do with compressor surge?

Loosen your BOV. I have some compressor surge and I think it sounds sexy. Didn't have it until I tightened my BOV.

[s13sr20chris]

[QUOTE=RMiller]What does boost control have to do with compressor surge?

QUOTE]

oops, meant to be asking the boost pressure as well. more or less wondering if he was running lots of boost. my turbo surges at 13 and not at 7. that and my bov is pretty loose. i have not bothered to mess with it much lately though its on my list.

[Nismo_Freak]

What does boost control have to do with compressor surge?

Loosen your BOV. I have some compressor surge and I think it sounds sexy. Didn't have it until I tightened my BOV.

Boost control has everything to do with compressor surge.

His issue is when the turbocharger is building boost pressure, not when he is shifting and the BOV is not opening.

The only things that can cause a small turbo like the T25 to surge at low boost pressures is an obstruction to flow on the compressor side or faulty wastegate operation as a result of a boost controller setting, etc.

I would set the gain and any of the other response features of the AVC-R to a lower setting, this should prevent this issue.

[Nismo_Freak]

What does boost control have to do with compressor surge?

QUOTE]

oops, meant to be asking the boost pressure as well. more or less wondering if he was running lots of boost. my turbo surges at 13 and not at 7. that and my bov is pretty loose. i have not bothered to mess with it much lately though its on my list.

I have never experienced turbo surge on any T25 powered vehicle when used within a normal pressure range.

However my definition of compressor surge is when the turbocharger is building boost and falls in the surge area of the efficiency map. This is typical on lower boost targets and aggressive response on larger turbochargers. Case and point, trying to get a T70 to make 1 bar.

Compressor backwash is a form of compressor surge by definition though, but when I read compressor surge I tend to think of it as what I mentioned above.

[yellow_jacket]

Thanks for the help guys. I will try dialing in the boost controller a little better to see if I can solve it. As far as obstructions go I can't imagine there is anything, but I'll have to get my other filter recharged and installed.

[s13sr20chris]

I have never experienced turbo surge on any T25 powered vehicle when used within a normal pressure range.

However my definition of compressor surge is when the turbocharger is building boost and falls in the surge area of the efficiency map. This is typical on lower boost targets and aggressive response on larger turbochargers. Case and point, trying to get a T70 to make 1 bar.

Compressor backwash is a form of compressor surge by definition though, but when I read compressor surge I tend to think of it as what I mentioned above.

honestly i never really believed that it was compressor surge but i watched that clip of the high powered s14 and some guys were saying the weird flapping noise was compressor surge. i have that noise when my bov is operating and i know for a fact i have a piece of metal hampering flow slightly in my hotpipe. i know because i made the pipe in a big hurry. i dont know if its surging or not but the darn thing goes flap-flap-flap-flap when i shift.

[Nismo_Freak]

honestly i never really believed that it was compressor surge but i watched that clip of the high powered s14 and some guys were saying the weird flapping noise was compressor surge. i have that noise when my bov is operating and i know for a fact i have a piece of metal hampering flow slightly in my hotpipe. i know because i made the pipe in a big hurry. i dont know if its surging or not but the darn thing goes flap-flap-flap-flap when i shift.

When he shifts that is compressor backwash from the pressure not opening the BOV, but that isn't really compressor surge during operation which sounds like a loud muffled chirp so to say.

With my Blitz BOV the spring is tight enough that even at low boost pressures (1-2 psi) it still opens. I only get that surge flutter if I get on it a little and release the pedal before the boost gauge registers positive boost. In that instance the BOV opening isn't going to do anything for response, and a little compressor backwash isn't going to hurt the turbo. Now if you can't get the BOV to open at 14 psi then yes, you got an issue lol.

[RMiller]

Thinking back to MAD's S14 (the super high powered one) it makes that fluttering noise, which must be caused because the compressor made lots of boost then quickly stopped. The compressor is not longer forcing air, so it doesn't apply pressure away from the compressor and the remaining pressure in the system can go backwards toward the compressor. I suppose the BOV can't accomodate all the pressure above atmospheric that is left, so the air takes the path of less restriction, which is back to the turbo since it's too hard to exit through the BOV.

This would only happen when the turbo slows its spool to the point where it is less restrictive to go backwards than out the BOV, so between shifts it probably wouldn't happen, as the turbo slows it's spool for a moment, then starts up again. That's why you hear the fluttering after the car makes boost and then the driver lets off the throttle entirely.

I think both the muffled chirp and the fluttering may be the same thing. If the BOV is too tight, then it may not open when it registers vacuum in the intake manifold. So the pressure goes backwards.

Ahh, I'm talking about nothing now. I assumed he was talking about the fluttering you hear when you get on it a little, then let off. I missed the part about it not being between shifts, my bad. In my car, I hear a little fluttering from surge if I hit a few psi, even 6. I didn't hear the surge until I tightened my BOV.

And finally, heh, I see what you mean by boost control's relation to compressor surge. But I assume yellow_jacket isn't getting boost spike. So if boost is under control, then it must be what Nismo_Freak mentioned about a restriction near the compressor.

[Nismo_Freak]

Thinking back to MAD's S14 (the super high powered one) it makes that fluttering noise, which must be caused because the compressor made lots of boost then quickly stopped. The compressor is not longer forcing air, so it doesn't apply pressure away from the compressor and the remaining pressure in the system can go backwards toward the compressor. I suppose the BOV can't accomodate all the pressure above atmospheric that is left, so the air takes the path of less restriction, which is back to the turbo since it's too hard to exit through the BOV.

This would only happen when the turbo slows its spool to the point where it is less restrictive to go backwards than out the BOV, so between shifts it probably wouldn't happen, as the turbo slows it's spool for a moment, then starts up again. That's why you hear the fluttering after the car makes boost and then the driver lets off the throttle entirely.

I think both the muffled chirp and the fluttering may be the same thing. If the BOV is too tight, then it may not open when it registers vacuum in the intake manifold. So the pressure goes backwards.

Ahh, I'm talking about nothing now. I assumed he was talking about the fluttering you hear when you get on it a little, then let off. I missed the part about it not being between shifts, my bad. In my car, I hear a little fluttering from surge if I hit a few psi, even 6. I didn't hear the surge until I tightened my BOV.

And finally, heh, I see what you mean by boost control's relation to compressor surge. But I assume yellow_jacket isn't getting boost spike. So if boost is under control, then it must be what Nismo_Freak mentioned about a restriction near the compressor.

You just said what I said lol...

BTW, in that video the fluttering when he is on the throttle is from the engine misfiring not compressor surge. Compressor surge under load sounds different and is not as a result of a BOV problem, it's a sizing problem.