Hey guys,

Just got a 3" exhaust fitted from the turbo back. I love it. It sounds great. However, now that I can hear the turbo a lot better, I've noticed an issue the past couple of nights driving around.

When at full throttle, it almost sounds like I can hear the turbo surging. I'm not sure if this is compressor surge, but the best way I can describe it is that it's a sort of pulsating noise. It only happens at full throttle when I am hitting around 13 psi. It also seems like the boost gauge I have installed vibrates coincidentally with this noise. The variation in pressure is probably around 0.5-1 psi. It won't do it in first gear (at 10 psi), but whenever I boost above that in the higher gears it seems to happen.

Anyone know what could cause this? It seems to be like it could be the T-VSV since it won't happen at 10 psi. Any self-tests I can do to find the culprit?

Another interesting phenomenon I get is that sometimes, not always, boost will build to 10 psi quickly and then kind of pause there, and then it will hit 13 quickly. I'm kind of thinking the two issues are related somehow.

Car is a 94 st205 WRC completely stock aside from the 3" tubo-back.

Thanks
Nick

Am experiencing the exact same issue, am getting that pulsating kinda noise. Am thinking its the T-VSV, sounds like its struggling to keep the boost at 13psi

is the power delivery still smooth though?

from what it sounds like, now that you've opened up the exhaust the turbo wants to boost more but your wastegate and t-vsv are doing their job

precisely my thoughts

Power delivery is still smooth as far as I can tell. It's strange....sometimes I can hit 13 psi in 1st gear.

It definitely sounds like a solenoid of some sort, which is why I'm thinking it has to do with the t-vsv. So it would be considered normal to hear the t-vsv's duty cycle at full boost then?

I'm about to put the avcr in the car (once I can get some decent switches for it). Once I've got the t-vsv disabled, I'll do a few runs just on the wastegate and see if I can hear it.

Thanks for the replies. I appreciate it.

Nick