as title i want to replace the n75 valve on my mk1 vrs and replace with a new n75j valve, iv been having a look around on here and cant seem to find any info on where the valve is and a bit of a guide to removal/fitting etc?

 

any help much appreciated 

The N75 is the part at the top on the right with the electrical connector going to it. Tbh its easy to remove. Two pipes and the plug.

Fantastic thanks alot fella i can do this same time as diverter valve then.

Sorry to steam in, but could the n75 be related to my car not holding boost after 5200rpm? I still think it's actuator spring to be honest but the n75 isn't that expensive and an easy renewal so may do it as a matter of course.

I have seen conflicting part numbers though and believe the wrong one for the requested boost can cause issues. I'd rather keep it as the one the car is supposed to have but is that right for a request of 19 psi?

It may not be the problem, I'm just interested and throwing it out there as said I may renew it as a matter of course.

Yeah right next to it. I'm sure the j version is for higher boost though so I'm not sure if it'll make any difference.

Is it worth me fitting the j version on a stage 1 mapped car or just fit a new standard vrs one?

Is it worth me fitting the j version on a stage 1 mapped car or just fit a new standard vrs one?

I suppose that's the more concise version of my question lol

Sorry to steam in, but could the n75 be related to my car not holding boost after 5200rpm? I still think it's actuator spring to be honest but the n75 isn't that expensive and an easy renewal so may do it as a matter of course.

I have seen conflicting part numbers though and believe the wrong one for the requested boost can cause issues. I'd rather keep it as the one the car is supposed to have but is that right for a request of 19 psi?

It may not be the problem, I'm just interested and throwing it out there as said I may renew it as a matter of course.

Tbh I'm not entirely sure what it does! I have read stuff on it I think it does control boost so i suppose your issue could be in some way related to your low boost issue. And it'll be easier to change first. Like ive said above the j version is for extremely high boost levels as far as i know the standard N75 is fine for stage 1 tune.

Tbh I'm not entirely sure what it does! I have read stuff on it I think it does control boost so i suppose your issue could be in some way related to your low boost issue. And it'll be easier to change first. Like ive said above the j version is for extremely high boost levels as far as i know the standard N75 is fine for stage 1 tune.

Cheers I had heard normal one is fine for stage 1, that's the E isn't it?

Ooo edit, it's F isn't it?

Oe n75 it is then thanks guys

Oe n75 it is then thanks guys

May not be as straightforward as that after all

http://www.briskoda.net/forums/topic/311010-n75-valve-what-revision/

worth a read and possibly more exploration. Standard should be fine but that 15 psi mentioned limit is slightly concerning

http://www.briskoda.net/forums/topic/154131-n75-j-valve/

Within there it does say F which I think is revised as E is fine. That's the one fitted to the 225bhp so should be ok.

Didn't realise it was such a minefield.

What boost are stage 1 cars mapped to?

Also the hose that goes into top of diverter valve what diameter is that as id like to replace with silicone and also the hose coming off it to the left

Mine requests 18-19psi, makes it but tails off after 5200rpm. I think it's actuator spring going soft and not able to overcome pressure and shut to hold boost. Having thought about this it may be related to n75. It's confusing because people say standard one is fine, others say the uprated oem one runs better yet others have major problems with fluctuating boost...to be honest I don't know what to think at the moment. If the F is fitted to 225 then as the standard one it should be fine technically speaking, whether it agrees with individual maps is another matter.

The original N75 fitted to the VRS was a C, which is now superceded by the F.

J valve will produce a steeper boost spike. My experience of running  Revo stage 1 with the J valve wasn't good as the car would go into limp when doing a standing start with any gusto.

N75 failure isn't very common so I would be wary of buying a new one before all other posibilities have been explored. Usual symptom of failure is jerky on/off boost under load.

The original N75 fitted to the VRS was a C, which is now superceded by the F.

J valve will produce a steeper boost spike. My experience of running  Revo stage 1 with the J valve wasn't good as the car would go into limp when doing a standing start with any gusto.

N75 failure isn't very common so I would be wary of buying a new one before all other posibilities have been explored. Usual symptom of failure is jerky on/off boost under load.

Cheers mate. I would have expected an n75 boosting issue would mean erratic and fluctuating boost. Mine just goes below specified but is still smooth.

What's your N75 duty cycle when boost is dropping off at high revs?

 

One of the many things I learn from Niki at R-tech during my second trip there recently is that it isn't always good to have the wastegate slammed shut to hold boost at high revs if exhaust gases can't flow out from the turbo easily. If there is a restriction, the boost will generate more heat, which is counter-productive. He actually reduced the N75 duty cycle to reduce boost at high revs and my car made a touch more power, as it had reached the limit of boost vs. efficiency. I think I've explained that right, he's a very clever guy.

 

Of course, it all depends on how well your hardware flows and mapping is incredibly important to take all this into account.

 

You could disconnect the N75 and just run it on actuator pressure to see how the boost behaves. Don't forget the logging. With a computer, not the other sorts...

What's your N75 duty cycle when boost is dropping off at high revs?

 

One of the many things I learn from Niki at R-tech during my second trip there recently is that it isn't always good to have the wastegate slammed shut to hold boost at high revs if exhaust gases can't flow out from the turbo easily. If there is a restriction, the boost will generate more heat, which is counter-productive. He actually reduced the N75 duty cycle to reduce boost at high revs and my car made a touch more power, as it had reached the limit of boost vs. efficiency. I think I've explained that right, he's a very clever guy.

 

Of course, it all depends on how well your hardware flows and mapping is incredibly important to take all this into account.

 

You could disconnect the N75 and just run it on actuator pressure to see how the boost behaves. Don't forget the logging. With a computer, not the other sorts...

Interesting, makes sense...I think. I expect there to be some tail off in the boost and don't really want to keep the actuator shut as such, I just want it to be able to shut at the right times, as it is dropping too much I feel. But then if the boost at high revs is reduced it's got more of a chance I guess. I was in conversation with r-tech asking their advice but it got to the point where I was basically asking for free diagnosis, not blatantly but you know...Anyway, what block do I need to measure for N75?

114 will show you the "Charge Pressure Solenoid Valve" as one of the readouts. And you probably know what block 115 does I guess?

Yah I have some graphs up in my dyno thread (pages 3 and 4 I think, my boost graph is on the last page) which is probably on page 2 of the forum list now. Do I need to log 115 with 114 then?

What I find strange is that people say you don't need modifications for stage 1 but that's not always the case it seems. The thing is the boost tails off but bhp and torque didn't get to where they should be at all initially. Just putting my thread in a nutshell putting the oem diaphragm back on with a known working MAF seemed to get the car pulling better. I logged 335nms and using the calculation worked out between 205 and 210bhp which is what I expected. Before this it only made 190 on the dyno with a fluttery line. My mate who was looking at the numbers extrapolated the MAF readings to predict 210bhp as well. It makes requested boost but falls below specified, quite gradually, you'll see from the chart it doesn't exactly fall off a cliff, but does drop too much. He thinks that this does nod towards a softening actuator spring. Looking at the original dyno reading I'm not sure turning the boost down would give me the 15 - 20 bhp I'm short of. Bit of a strange one, I'll log that block though and see what happens.

And actually, looking at the graph again specified boost does drop towards higher revs to around 15 psi then steady, so I don't think it is asking too much? Like I said I will check that block though.