N75J on a standard 1.8T?

[Bug_racer]

George is pretty close, it is modulated by the ECU to control the boost and in extreme circumstances will open the wastegate using stored vacuum to prevent any exhaust gas making it to the turbo.

http://s4wiki.com/wiki/N75

I forget which way round it is but I would say not to fit anything but the std one for your engine, unless the software has been specifically written for another valve.

There is a chance that a non-standard valve will cause the ECU a headache and put the car in limp mode.

Gavin

Deary me , we need a bit of a better explanation here as to how an n75 works , and I kinda guess we need an explanation on how the turbo works as well !


Everything either works on boost or a lack of it , there is no vacuum involved , the only vacuum in a turbo system is for the brake booster !

The exhaust gas exists the manifold and into the turbo . The turbo exhaust wheel is always spinning , if it wasnt spinning there would be very little intake air going in ! It spins to create positive pressure to pressurize the turbo hoses , intercooler , manifold etc . At this point the wastegate is shut until it can completely pressurize the system to the point at which it is ordered to . If the throttle is wide open it will continue pressurising until it reaches peak efficiency before it drops off (this is where you need to look at compressor maps to find out turbo flow/efficiency) . Say you back off the throttle when turbo is at max boost , the boost control solenoid is given a signal to open the wastegate of the turbo to decompress the exhaust side of the turbo . It uses the positive pressure in the outlet side of the turbo that feeds the manifold . The Diverter valve depressurizes the intake side that goes to the manifold . The DV uses the change in pressure from one side of the throttle body to the other to regulate the pressure coming out of the turbo into the manifold , some DBW cars use an electronic solenoid to open/close the DV . It then dumps the excess pressure back into the intake pipe . Which is also how the n75 works , it also allows some pressure back into the intake if it doesnt require the wastegate of the turbo to be completely opened .

Any Q's ?

[h100vw]

My explanation wasn't perfect, so thanks for sorting that out.

What's the score with the J valve, which was the original question.

Gavin

[madglf3]

Deary me , we need a bit of a better explanation here as to how an n75 works , and I kinda guess we need an explanation on how the turbo works as well !


Everything either works on boost or a lack of it , there is no vacuum involved , the only vacuum in a turbo system is for the brake booster !

The exhaust gas exists the manifold and into the turbo . The turbo exhaust wheel is always spinning , if it wasnt spinning there would be very little intake air going in ! It spins to create positive pressure to pressurize the turbo hoses , intercooler , manifold etc . At this point the wastegate is shut until it can completely pressurize the system to the point at which it is ordered to . If the throttle is wide open it will continue pressurising until it reaches peak efficiency before it drops off (this is where you need to look at compressor maps to find out turbo flow/efficiency) . Say you back off the throttle when turbo is at max boost , the boost control solenoid is given a signal to open the wastegate of the turbo to decompress the exhaust side of the turbo . It uses the positive pressure in the outlet side of the turbo that feeds the manifold . The Diverter valve depressurizes the intake side that goes to the manifold . The DV uses the change in pressure from one side of the throttle body to the other to regulate the pressure coming out of the turbo into the manifold , some DBW cars use an electronic solenoid to open/close the DV . It then dumps the excess pressure back into the intake pipe . Which is also how the n75 works , it also allows some pressure back into the intake if it doesnt require the wastegate of the turbo to be completely opened .

Any Q's ?

Thanks for that mate, good info. I too was wondering what it did.

[gpk_gti]

wow,the professor has spoken....too much info got a headache! hahhaa


I was running the n75j for a few weeks without a upgraded ecu without having any issues....

[No457 Snowy]

Following on from Seb's explanation, the way I always understood it as a "non-mechanic", compared to stock, the N75J is "slower" in opening the turbo's wastegate thus helping build a bit more turbo boost and keeping actual pressure most of the times above the ECU's requested pressure.

When you ask people that have done it, responses seem to vary, but in some cases if your stock ECU sees that as an "over-boost" situation it can put you into limp mode to protect the engine.

So after 2 pages of responses I think your question was really answered in the first two response posts.



Snowy

[gpk_gti]

come to think of it,thats another bit ill be selling!!!! forgot all about it!!!

[fuzion]

If you intend on chipping your car which im assuming you would be, grab a cheap one whilst you can before you do so. Put it on either way and slowly get everything together..

Its your choice int he end!

[schoona]

so is it like a re-circ BOV?

i say BOV as generic turbo speak, even though (if i understand correctly) it is en elctronically controlled DV?

[Blitzen]

so is it like a re-circ BOV?

i say BOV as generic turbo speak, even though (if i understand correctly) it is en elctronically controlled DV?

Not quite man. It has to do with the waste gate controlling, and nothing to do with the DV.

[Bug_racer]

Ok
lesson 2
I am not going to give my opinion just options !


The Mk4 Golf is drive by cable , most mk4 Golfs did not run the boost sensor which is located in the intercooler . Ive seen 1 so far with wiring hooked up , freak car maybe ? Anyway , with the mk4 due to the fact that the ECU does not know what boost is being made you can change the n75 to a J and it wont know you did so . In fact you could even run a manual boost controller and you wont get boost cut issues ! , but , the car does run a temp sensor in the intake manifold . The higher the reading the more fuel it dumps in to cool down the combustion . You need to remember that the lambda is also going to try and trim the fuel cause it will be running so rich but the factory maps will stop it cause its trying to protect the engine . Once you go over 10 psi its all hell , unless your chipped , thats the correct way to tune the engine , since your changing boost , fuel and ignition maps .

On cars which do have the boost sensor your restricted to about 12 psi before you hit hard limp mode . This is because when you have gone past a certain amount of boost that the ecu requests to what actually it is , it feels like it cuts ignition till it goes down to the max level . My assumption is its approx 3-4 psi more than what max stock level is , which is within the max amount that a upgraded n75j will give anyway . Im not completely sure on this as I hate "testing" a car this way to give optimum results with mbc !



I re-read what I wrote , sorry if I sound drunk ! I hope people have more of an understanding anyway