To make my Polo Stop Surging

[Petrina Polo]

Whats that got to do with the turbo??

Doesnt the turbo boost to a predetermined amount and any excess expelled through wastegate..

So pulling hose off would make turbo boost more but rather the excess amount not expelled..

I dont think it felt like another 10psi when i pulled the hose off.. just didnt surge..

whats the difference... that Cattaline bloke on this forum uses that flow restrictor to the N75.. therefore it expells excess boost leter than normal..

That wont make the turbo overboost..

[Spec83]

If the turbo overspeeds (and moves out it's efficency band) it's just producing more hot air for which the engine needs to retard ignition to prevent detonation = less power

[Plautos]

What Petrina is experiencing is the same felling of an N75Race, but a little more aggressive in medium and hi rpm’s.

It is not going to blow, surge our over speed the turbo. The WG actuator is too soft.

It is wrong to bypass the N75, doing this, there is no Limp Mode and no Traction Control, but is a way to feel the car with a stable boost.

[Spec83]

Isn't this dangerous as I imagine the ECU would use the N75 valve to gauge how much boost the turbo is making and adjust fuel and timing accordingly??

I would like to know more about the ellusive N75 valve

Found a simplified explanation -

Perhaps I was the only one on AW not understanding N75's integration into wastegate control and, more importantly, how to interpret group 114/115 logs and see if the wastegate is operating at its optimum. Not anymore. Hope the explanation below helps you too. Here goes:

The N75 is the valve that plays a large part in regulating the wastegate. An unenergized solenoid (0% duty cycle) permits full charge pressure on actuator diaphragm. So the turbocharger naturally regulates itself. As boost builds, the wastegate opens. The ECU can operate the N75 to vent some of this pressure so the wastegate either does not open, or opens less. For example if reading is 62.8% duty cycle it means over a 100 millisecond period (1/10 of a second) the charge pressure in the actuator line was filled for 37.2 milliseconds and vented for 62.8 milliseconds. An orifice in the charge pressure connection restricts the flow rate of charge air into the actuator system. If you are seeing a large difference between the two reading off block 115 (request high, actual low), and you see that duty cycle on the N75 is high (90-100% range), then you are probably leaking boost from a pressure hose (turbo outlet to intake manifold) or the diverter valve (DV). You should then check all clamps and hoses along the whole pressured tract as well as swap DVs.

So, when we look at, let's say, log 115 and see that actual boost is less than requested boost while ECU is yelling "somebody close that f%cking wastegate!" (N75 duty cycle close to 99%), we know there is a problem: either there is a boost leak, or the wastegate is not closing all the way (stuck)

Link - http://forums.audiworld.com/a4/msgs/2305772.phtml

[Petrina Polo]

Apparently there is an upspec N75? which stops surging.. from a golf or something??

What is this part and is it worth its weight?