N75 frequency?

[diesel des]

Ok, with vems I'm wondering what frequency people are setting the n75 up at. Not the duty cycle as this is obviously dependent on load, rpm boost etc, but the drive frequency. I think I'm at 50Hz.

Reason I ask is that I seem to get through a n75 a year. They start to get sticky, with boost being at sometimes wastegate setting, or a bit higher, but not the setpoint I have in the map. Wd40 sprayed through the ports helps for a while but really a new n75 is the answer.

I run a stock spring in my wastegate at 0.4 bar, and run 1.5 to 2 bar boost. Is this hard on the n75? Maybe a 1bar spring and less duty cycle in the n75 maps would help with life. Any thoughts? Cheers des.

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[prj]

20hz stock.

20.03 to be exact. 49920 cycles on a 12 mhz XTAL with a 1/12 prescaler.
3B has a 8mhz XTAL, haven't calculated on it though.

Duty cycle at least on the stock system is irrelevant because it makes exactly the same amount of switches.

[diesel des]

Thanks Dimitri. I'm just wondering if the n75 is having to work too hard to vent of 1.6bar to give me 2 bar boost with stock 0.4 bar spring. Have you ever had n75 issues on customers cars?

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[diesel des]

and where is best to get a valve. EBay is 65quid for a j valve.

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[UrS4boy]

N75 Wastegate Frequency Valve (WGFV) info

and where is best to get a valve. EBay is 65quid for a j valve.

034 906 283 J = stock 3B (in 200 20v and S2)
034 906 283 H = stock AAN (UrS4 and UrS6)
034 906 283 K = S2 ABY and RS2 ADU

I don't think you want a "J" valve. K or H and I think H turns out to be one of the best.

Read this: http://forums.audiworld.com/showthread.php?p=18772235

Linked out of this: http://forums.quattroworld.com/s4s6/msgs/20987.phtml

Which was accessed by clicking on the "N75" label in this live Engine Bay Device diagram:

http://members.shaw.ca/speedtek/UrS%20Engine%20Bay%20Device%20Map.html

[prj]

Thanks Dimitri. I'm just wondering if the n75 is having to work too hard to vent of 1.6bar to give me 2 bar boost with stock 0.4 bar spring. Have you ever had n75 issues on customers cars?

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Once again, it changes once for every period.
It does not run any harder whether you run 95% or 5% duty cycle on the stock ECU.
It's just in one position more than the other.

How it is implemented in VEMS I have no idea, but if after setting it to 20hz you still go through them like butter, then either VEMS does not drive them correctly, or what is far more likely, the location of your valve is not optimal.

As for different letter codes of valves - makes no difference whatsoever in my experience.
To satisfy my curiosity I tested five or six different valves at some point, and there was absolutely no difference other than having the connector in a different place.

[diesel des]

Dimitri I understand what your saying, but by having to put say 95% duty cycle into a valve to get the output you want is supplying more energy and heat etc into it than you would with say 50% duty. That's the electrical side. On the mechanical side, driving the valve almost fully against its spring for long periods might cause weakening of the spring or other damage to the valve from the long stroke.

Even at 20Hz, with 50% duty I can't see the valve actually moving internally 20 times a second, I just think we are positioning it approximately 50% open. The inertia of the internal parts will average out the pulses a little.

With cars running up to 2 bar boost do you recommend upgrading the wastegate spring? Or have you any thoughts on what's the best time to increase that setpoint?

Cheers des


I don't know, just putting out ideas.

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[diesel des]

Urs4boy, I think its a j valve I have now, so I have my maps optimized around it. I don't think the revision makes a huge difference if your using pid closed loop boost control like vems or motronic. Maybe a slight spike, or whatever, but nothing major.

Dimitri, the n75 is in the stock position only car.

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[prj]

Dimitri I understand what your saying, but by having to put say 95% duty cycle into a valve to get the output you want is supplying more energy and heat etc into it than you would with say 50% duty. That's the electrical side. On the mechanical side, driving the valve almost fully against its spring for long periods might cause weakening of the spring or other damage to the valve from the long stroke.

Even at 20Hz, with 50% duty I can't see the valve actually moving internally 20 times a second, I just think we are positioning it approximately 50% open. The inertia of the internal parts will average out the pulses a little.

With cars running up to 2 bar boost do you recommend upgrading the wastegate spring? Or have you any thoughts on what's the best time to increase that setpoint?

Cheers des

I don't know, just putting out ideas.

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This would be relevant IF it maybe was a track car under WOT operation only.
On a daily fact of the matter is, the valve does sod all for the majority of it's lifetime.
And for when you push the throttle, it is 95% open all the time anyway until setpoint is reached on any car.

I never had electrical problems with N75 valves, low boost or high boost, or any mechanical problems.
Maybe VEMS is not driving it correctly, maybe you have some other problem.

With the stock ECU these valves live for more than 10 years without failure. I told you what frequency it runs. I also told you that I strongly disagree with the fact that how much boost it produces has measurable lifetime differences...

That's it. If you don't like the factory valve or your ECU does not work well with it, try a different valve. My experience is that other valves are a lot tougher to control than the stock valve, as it is built for a very good response.

P.S.
There is one thing - the stock ECU never drives the valve over about 98%.

[diesel des]

Dimitri, I have never had any electrical issues with the valves, it's the mechanical side that gets sticky. I have changed the frequency to 21Hz to see if that makes any odds. I also have vems set not to use the valve untill map gets above 1100bar abs so it's not using the valve all the time. I think vems does goto 100% duty though, so maybe that hurts things a little, but compared to motronics 98% it's hard to see much difference. Maybe the output circuits in vems are more harsh. Job for the scope...

I do think that if the n75 is having to dump more air it is bound to have higher flow, higher pressure differential and maybe damage to the mechanical valve seat would occur over time. I could reduce the pressure differential and flow by upgraded the wastegate spring. So have you mapped many cars at 2bar boost on the stock spring?

Cheers des.



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[prj]

Dimitri, I have never had any electrical issues with the valves, it's the mechanical side that gets sticky. I have changed the frequency to 21Hz to see if that makes any odds. I also have vems set not to use the valve untill map gets above 1100bar abs so it's not using the valve all the time. I think vems does goto 100% duty though, so maybe that hurts things a little, but compared to motronics 98% it's hard to see much difference. Maybe the output circuits in vems are more harsh. Job for the scope...

I think not pulsing the valve at all until the map goes up is not a good idea.
Motronic starts pulsing it the moment there is some boost request. I also think going to 100% duty is a horrible idea.

I do think that if the n75 is having to dump more air it is bound to have higher flow, higher pressure differential and maybe damage to the mechanical valve seat would occur over time. I could reduce the pressure differential and flow by upgraded the wastegate spring. So have you mapped many cars at 2bar boost on the stock spring?

I disagree. I have mapped every kind of possible and impossible combination you can think of, and none of the cars have N75 issues. Also, 2 bar you are going to see only for a minute amount of time on the stock spring, as backpressure pushes the wastegate open.
I don't see what pressure differential has to do with anything. With a high duty cycle the valve is operating in full bypass mode, and the only place there is any pressure differential at all is the restrictor at the bottom port. Remember, at high duty cycle all ports are open so air can freely flow back into the intake. You are aware that the flow through the N75 is completely irrelevant due to the tiny restrictor in the bottom port, aren't you?

I also have not heard of people using VEMS have issues with N75 valves.
Maybe you should look closer at your setup and how much heat gets to the N75.

But hey, if you feel like chasing ghosts, be my guest. I don't think I have anything to add to this thread at this point.

[Mcstiff]

You can set the max DC to 98% in the PID Settings. I am not using an N75 (I never had one) so I don't know much specific on them.

[A80Avant]

I don't remember what is the frequency in mine as I haven't looked at my laptop for a while. I don't use stock n75 anymore but a mac valve 3port and have never had any issues with boost control. My setup doesn't need to go to 100% either but I do have a stiffer spring though.

Having said all of the above I never had issues with the stock valve either and from memory at the time I was using vems with a very early firmware and I'm never sure of what the hz were or if they had any significant meaning. With the 3071R at the time boost control was nicely managed.

[Val]

I don't think you want a "J" valve. K or H and I think H turns out to be one of the best.

Doesn't matter for vems. It just have to be in working condition...
Mine runs @ 21Hz.

[diesel des]

Thanks for all the input guys. I will try the new frequency and try limiting duty to 98% and see what n75 life is like. If it screws up again I will upgrade the spring and play with the map.

Dimitri, just one more time. Are you happy to map cars with stock spring up to any boost, or do you have a cut off point. Obviously a tighter spring alongside a higher duty cycle speeds up.spool to a point. Just wondering with my 2 bar through the mid range on a gtx2867r should I upgrade the spring in my wastegate with a 1 bar one that lives in my glove box, so no expense.

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