chrykies

4Driver4 - I wanted to carry this discussion a little further. I'll sum up the operation of the "Wastegate Bypass Regulator Valve N75":
1. The wastgate allows exhaust gas to bypass the turbine when charge pressure fills the 'secondary chamber', as previously described (in part);
2. The ECU calculates the proper/desired boost pressure (through the pressure transducer mounted on the bottom board of the ECU), and sends an output signal to the N75 valve, which the "operates" to supply the secondary chamber with charge (boost) pressure to open the wastegate.
3. When the ECU is prepared to again allow boost, the ECU allows the N75 valve to "close" and vent back to the turbo inlet, thus allowing the wastegate to close.
4. The N75 valve operates on a duty cycle, but continously operates (open/close).

The speed at which the N75 operates dictates, in part, the ECU's ability to measure/relieve excess manifold pressure and return to boost. A faster N75 does not cause the wastegate to open/close faster or more efficiently. The speed at which the N75 operataes, however, can prevent boost spikes registered by the ECU's pressure transducer. When the pressure transducer registers a boost spike, the ECU responds by dialing back timing and "opening" the N75 valve.

Also, different N75 valves have smaller/larger orifices through which charge pressure is supplied/relieved, which work in conjuction with the valve's duty cycle to supply/restrict charge pressure to the secondary chamber. The N75 "K" valve is valve specified for RS2 turbos on 3B/AAN motors.

In the FWIW category, I recall a dyno chart that pitted an N75 "K" valve against the stock N75 valve ("G"?) on a 2001 VW Golf (1.8t, AWW engine). At about 3900rpm, the N75 "K" valve developed over 20lb-ft more torque and 14whp more than the stock valve.

Bear in mind that no matter what N75 valve you have installed, your wastegate will open to relieve excess manifold pressure at a pre-determined pressure (depending on what wastegate spring you have installed). Thus, "tightening" down your spring only allows for momentary boost spikes.

The BPV is a recirculation valve actutated by manifold vacuum. During deceleration and/or shifts, the motor enters a vacuum state, which "stalls" (momentarily) the compressor side of the turbo. Lifting the throttle at high revs creates engine vacuum sufficient to overcome the spring pressure inside the BPV, pulling "open" the BPV. This allows charge pressure created by the spinning compressor to be recirculated back to the turbo inlet. By recirculating charge pressure, you reduce compressor stall, which allows for smoother operation of the turbo and reduces overall turbo "lag".

4Driver4

and maybe some of the other stuff, but not all of it.

"The speed at which the N75 operates dictates, in part, the ECU's ability to measure/relieve excess manifold pressure and return to boost."
I disagree. The correct statement is:
"The speed at which the N75 operates dictates, in part, the ECU's ability to relieve excess manifold pressure and return to boost."
The speed of the frequency valve has nothing to do with the ECU's ability to measure manifold pressure.

"The speed at which the N75 operataes, however, can prevent boost spikes registered by the ECU's pressure transducer. When the pressure transducer registers a boost spike, the ECU responds by dialing back timing and "opening" the N75 valve."
I agree with this one (for the most part), but a faster N75 doesn't conversely translate to better WG control. If the ECU puts out a pulse at a set rate, being able to receive it faster doesn't help. Go back to my typing analogy: it doesn't matter if you can listen faster than the guy next to you; you are both limited by the speed at which I talk. One of you cannot finish listening earlier.

"Also, different N75 valves have smaller/larger orifices through which charge pressure is supplied/relieved, which work in conjuction with the valve's duty cycle to supply/restrict charge pressure to the secondary chamber."
This is something worth investigating. If the K valve truely has a larger orifice, then it may be able to flow more charge to the secondary chamber...assuming that the valve is the limiting variable in the "pipeline".

"In the FWIW category, I recall a dyno chart that pitted an N75 "K" valve against the stock N75 valve ("G"?) on a 2001 VW Golf (1.8t, AWW engine). At about 3900rpm, the N75 "K" valve developed over 20lb-ft more torque and 14whp more than the stock valve."
Possible. But I'm not sure if the Golf data (if reliable) can translate to our cars. The Golf ECU may have tighter control over the WGFV.

All this discussion begs for someone to test this on the dyno. Any volunteers?

a4kquattro

Alex offered to let me try a K valve on the dyno but I never got around to swapping it (it would have messed with the data anyway as I was trying to obtain data on the FMIC kits me and Tom are working on).

Some perhaps useful and perhaps worthless information on the WGFV.. while re-plumbing my intake hose setup post 'big' turbo install with the 2B inlet hose and I discovered something interesting about the WGFV (I'm using the stock valve). If I had any sort of extra hose run between the valve outlet and the turbo inlet hose I lost an honest to goodness 6 psi of peak boost. I discovered the flaw after installing the turbo and wondering what the hell happened to my top end boost. After fumbling around under the hood I allowed the valve to vent to atmosphere and my peak boost came back to the way it was with my previous turbo.

So if anything, larger hose connections on the valve COULD lead to something performance wise.. The fact that there was a slight extra resistance on the return line caused the valve to bleed boost onto the wastegate control line, opening the wastegate prematurely.

I'll try to put a K valve in at some point to see if it makes any difference.

chrykies

I like the speaking vs. listening analogy.

In stock form, the wastegate hears the N75 just fine.

Add an RS2 or comparable turbo, and the N75 suddenly develops a speech impediment that the WG, despite its hearing aid (spring), has difficulty hearing. Hard to hear with all that wind, you say? Hear, listen to my K valve.

You see, the stock N75 speaks broken english when you shove a big turbo down its throat. The ECU expects its output signal/duty cycle and the N75's charge orifices will meter a pre-determined amount of charge into the secondary plenum to open the stock wastegate.

When you upsize the turbo, the wastegate operation is still functioning at a snail's pace, which causes nasty boost spikes.

So, maybe the best explanation is that the uprated N75 valves do not per se "speed up" wastegate action; the K valve simply ensures wastegate operation that accounts for larger volume of charge air, reducing the occurrence of boost spikes.

Yet another view: the stock N75, together with a larger turbo, ensures that the wastegate opens/closes less efficiently than stock turbo/n75 combination.

Does the N75 "K" open and close my wastegate faster than the "H" valve? You betcha. Not only can it be heard, it can be felt, and it can be seen both on the boost gauge and the dyno sheet.

zVMAP

Who's Legend????

If you are having an issue due to a sticky valve and the stock one costs $80.00 but the "K" solenoid costs $90.00 ... by the K version ... otherwise ... toss the legend out the window.

come on guys this is a mechanical solenoid that opens and closes the wastegate!

Your spring adjustement on the Wastegate has more of an influence than a "K" valve.

.....

Mihnea

What you're telling us about the golf is that the K valve is slower to react than a golf (G???) N75, which means boost spikes can't be controlled as easily as the ECU normally can with the stock valve. So all this tells me is that if you want a faster valve, you need the golf one, not the K one.

The other issue is that the ECU cannot always react quickly enough, simply because it takes it a while before it figures that actual boost is higher than target boost, BTDT and the K valve is then no better than a stock valve.

I have done countless RS2s last year with brand new valves where I would get boost spikes and the ECU couldn't control them properly because the duty cycle on the N75 wasn't correct (that was my fault), after correcting the WGFV duty cycle map properly, no more spikes. The same has happened to me in the US with RS2-ed S4s where we would have the same behavior, we changed valves to make sure they were new, then mapped properly the N75 duty cycle map and that was it, no more spikes.

Now what's the point here? Trying to use a better valve in order to correct a tuner's programming fault?

As I said earlier, if you're looking for a faster valve, don't use an old type of valve (no matter if it was designed for an RS2 or not), use a brand new one from a TT. But I'm not sure that the ECU will be able to take advantage of it. The TT ECU can take full advantage of that valve, but this is because of the very accurate boost control of the TT ME7.5 ECU, which our poor M2.3.2 ECUs don't have....


HTH,

Mihnea

Mihnea

you are so right Feico. I fully agree with you!!!!

4Driver4

then it is hard to argue that it doesn't do anything. The only thing that would make sense to me is that it must have a larger orifice. The H valve must be only able to open a certain amount, while the K valve can open "wider". This, of course, assumes that tubing to the WG is large enough to handle the increased volume, which apparently it is if you feel the difference.