# Understanding N75



## Sim (Jun 27, 2002)

Guys,
As i see many of you are totally confused about the N75 valve (what it does, how is it working), just exactly as i was before digging myself into the topic quite deeply. My car was seriously down on power - i even posted some desperate topics here too, but noone was able to give me any usable suggestions/answers. At the end, i found that there was some problem with my N75 valve (though it was working OK) which prevented the car to produce more boost than stock.
So, if any of you has problems with the N75 valve - or just got problems but don't really know what is it related to, then read more further.
The turbo, the boost it produces, the N75 and the ECU.
These are the most important things which you have to focus on. As we know, we got a turbo on our engine which produces boost. The turbo is "driven" by the exhaust gasses our engine produces. Exhaust spools up the turbine in the turbo which is mounted on the same driveshaft as the compressor which then generates boost. I persume it is all clear for everybody.
There is a wastegate on our turbos (as usually on every turbo) which looks like a simple valve, just exactly like in the cylinderhead. There's a difference though, the valves in the head are operated by the cams, the valve (wastegate) in the turbo is operated by pressurized air. When pressurized air is introduced to the wastegate, it will open, enabling the exhaust gasses to escape and skip the turbo. This will result in a dramatical loss of boost, because there will be no gas which would spin the turbo. I bet this is (was) also clear for everybody.
But how is this all hooked up???
Quite simply. The wastegate is operated by the turbo itself. The boost the turbo produces is directly fed to its own wastegate. What does this mean? When the turbo spools up, it will create boost and this boost will open its own wastegate, shutting itself automatically down.
But where's boost control? And wheres ECU?
Here comes the N75 valve. The N75 valve is inserted between the turbo's high pressure output and the wastegate. If the turbo would directly linked to the wastegate, it would not be able to produce lets say more than 0.3-0.4 bar of boost, because it would shut itself down immediately. When the ECU wants more boost (because you are stepping on it for example), it WENTS some air from this loop (turbo--->wastegate) so the wastegate will not open at all, or will open later.
The N75 has got 1 boost input, and 2 outputs. At the input, boost is entering into the N75 and exits on one of the outputs going to the wastegate. When N75 is closed (default state), all the boost goes to the wastegate. When ECU opens the N75 valve (because it has got an electrical plug too coming from ECU), so when ECU opens it, some of this boost (which would operate the wastegate) is leaving/leaking back to the inlet (and not opening wastegate). Since the N75 valve has NO state in between, is is opened or closed. The ECU switches it ON/OFF all the time (several times a second) to generate the desired amount of boost. Doesn't it reminds you to something???? ... Yeah, it's surging. But it is absolutely normal, this is how ECU controls the wastegate. When a car is chipped, the boost is a LOT higher than it is designed to operate on, so this kind of boost control will be noticable.
By adjusting the N75 valve, you can adjust the amount of air which should leave when the N75 is opened. If you adjust the N75 to the right, you will "close" the N75 valve, so just a few amounts of air is wented from the wastegate which will result in a lot smoother drive (eliminating surging, because the boost will be more constant), BUT at the same time it will introduce more boost to the wastegate, causing LESS overall boost. Adjusting the N75 valve to the left will "open" it, enabling more air to escape from the wastegate when N75 is opened, which will result in more boost (coz wastegate wont open), BUT at the same time it MAY cause surging as the N75 opening/closing will be more obvious.
And finally, here are some useful links to our forums where we dealt with some problems which helped us to understand the operation of the N75 valve.
http://www.seatcars.net/forums/showthread.php?s=b093d32039884f84fdb3166f9a680051&threadid=6680
http://www.seatcars.net/forums/showthread.php?s=b093d32039884f84fdb3166f9a680051&threadid=7210
http://www.seatcars.net/forums/showthread.php?s=b093d32039884f84fdb3166f9a680051&threadid=7417


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## SlvrBllt (Oct 15, 2001)

*Re: Understanding N75 (Sim)*

Good summary http://****************.com/smile/emthup.gif


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## bigbwoy (Apr 29, 2000)

*Re: Understanding N75 (Sim)*

Thansk for that explanation Sim. I have added it to my notepad. http://****************.com/smile/emthup.gif


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## RVs021.8T (Oct 11, 2001)

*Re: Understanding N75 (bigbwoy)*

quote:[HR][/HR]Thansk for that explanation Sim. I have added it to my notepad. http://****************.com/smile/emthup.gif [HR][/HR]​ http://****************.com/smile/emthup.gif


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Sim)*

BTW, i am now working on an interesting tuning N75 project. 
read about it here:
http://www.seatcars.net/forums/showthread.php?s=b093d32039884f84fdb3166f9a680051&threadid=7417
I will do the trick possibly this week (as ill have more time).


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Sim)*

Ahh yes, i alsmost forgot:
HOW to adjust your N75 valve:
- The screw in some N75 valves are glued in, so first you have to break this glue to be able to move the screw. After breaking this glue, N75 adjustment will be still hard in most of the cases.
- Then always try to move it counter-clockwise first (to the right), as usually N75s are widely opened by default -- set to the leftmost position (when surging).
- Then some N75 valves DO NOT MOVE when hot. You have to wait until the whole engine cools down completely 100%!!!
- Then there are lots of posts telling; do not touch your N75. They do have got some reality, too much adjustments on them (not big movement, but many times of fooling around) may actually cause them to not to work anymore. ECU will not throw a fault code because the coil (which operates a piston inside) wil be still working (no broken circuit or anything), something inside just gets stuck and it will not went air from the wastegate at all anymore. This will cause 0.3-0.5 bar of boost maximum wherever you set the screw.
HINT: Check out the local prices and availability of the N75 valves first


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## Golf 2 Slow GLS (Aug 7, 2001)

*Re: Understanding N75 (Sim)*

So how do the C N75's and F N75's differ? Is it where they are set or is there something actually physically different?


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Golf 2 Slow GLS)*

I have not had the fortune to meet with an F version yet. I got two C valves to play with. There is a restriction in the N75 valves. This means that the boost controlling the wastegate is entering the N75 only on a small ~2mm diameter restriction, so not all boost is used to control the wastegate. I suspect there should be differences in this restriction. The C valve got (so should the F one) a visible small restriction hole where air enters in it. This hole is about ~2mm in diameter on the C valves. Could anyone check his with an F one?
I think the F valves should have a little bit bigger hole in it. More boost is used to control the wastegate, therefore surging is more noticable. Don't know this yet, this has to be still veryfied.


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## Mr_gimble (Jun 14, 2000)

*Re: Understanding N75 (Sim)*

I made a crude picture.


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## RVs021.8T (Oct 11, 2001)

*Re: Understanding N75 (Mr_gimble)*

Bump. Sim, you said to turn the screw to the right (counterclockwise) don't you mean the opposite?
And if you adjust this valve while stock. If I say turned it to the left some, so it was set at say 10 oclock, whereas right now mine is set at 12oclock (F valve) would adjusting it, increase more air thus producing any more power while stock?? Or not.


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## H2O WOLF (Mar 30, 2000)

*Re: Understanding N75 (Sim)*

That's sweet. Thanks for posting your work. http://****************.com/smile/emthup.gif


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (RVs021.8T)*

Gimble,
your picture seems to be right, tho your remarks need to be corrected. The N75 can not direct boost just to the red way. It will always allow air to go to the wastagate (the blue way is always opened). When 12V DC is switched to the N75, it will open the red way too. That's all N75 does! The BIG problem with our N75 is that it cannot adjust the amount of boost which has to leave thru the red way (you gotta do it manually with the screw), so it is either boosting or not boosting. This is surging.
Heres a more precise picture how's this all hooked up:








The duty cycle 0-100% does not mean the amount of air which should leave from the wastegate, but it represents time intervals. How long should the N75 stay opened/closed. It is usually just a fraction of a second (usually switches 10 times a second).
RVs021.8T,
adjusting the N75 on stock cars does not necessarily mean more boost. When ECU detects that the requested amount of boost has been already reached, it will close the N75 (so all boost is directed to the wastegate to open it, preventing turbo from making any more boost). When the N75 is in closed state (which is its default state), the screw and its position doesn't play any role - wherever set. If N75 is knackered, it won't open anymore allowing all boost going to the wastegate opening it.








This picture shows the N75 valve opened, when that piston like thing in the middle (light gray with white middle) is pulled up by an electric magnet (coil). When closed (default state), that piston goes down (by some spring or anything), preventing boost to "leak or bleed" out through the purple way. It is basically a controlled bleed valve. If the screw is adjusted to the right, it moves inside the N75, making the piston to move less, giving just a small gap for the boost to escape. If the screw is adjusted to the left, it moves outside so that piston can open widely so lots of air can leave thru the purple way. That's good, because wastegate will open later, but may surge as we know.


[Modified by Sim, 11:26 PM 7-30-2002]


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## RVs021.8T (Oct 11, 2001)

*Re: Understanding N75 (Sim)*

Okay, Sim, so there would be no point in adjusting the valve for more boost. Just wondering.


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (RVs021.8T)*

Absolutely no point. You're not the first one who asks this tho.


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## Jeckyll (Feb 24, 2002)

*Re: Understanding N75 (Sim)*

Nice job!
Every once in a while there is a post that makes you realize that not all your time on vortex is wasted


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## xray_boy (Jun 22, 2001)

*Re: Understanding N75 (RVs021.8T)*

what people keep forgetting is that the 1.8T uses a closed loop system to monitor boost. eg: ECU requests 1600bar then it uses all its resources (N75, DV) to reach that level, monitors it with the charge pressure sensor (MAP in intercooler) and then holds it there. It can modulate the frequency going to the N75 to increase boost, or dump boost with the DV. Does everyone forget all the posts about people adjusting the N75, then a week later the surging is back? I dont see how putting a restrictor inline with the wastegate hose (after N75) will net you more boost. the ECU still requests 1600bar (eg.) and uses its resources to monitor and regulate that specified level. you may be able to soften the system to get less spikes, but it all depends on where the spikes are coming from. The ECU is controlling the system, if it doesnt have the brain power to controll it fast enough then there will be lag in the outputs and you can get surging. (this reminds me of back in college when we designed systems to controll cruise controll systems or water levels exiting resevoirs.)
the question is why do some cars surge and others dont? usually its with the aftermarket chips that surge. maybe they just cant program as well as the germans. maybe some wastegates move a little more freely than others and a binding wastegate arm will cause delays and spikes?
does anyone know the insides of the ECU? what logic it is using? what kind of controller (in college we just used the very basic old 8088 processors)

[Modified by xray_boy, 9:18 AM 7-30-2002]


[Modified by xray_boy, 9:25 AM 7-30-2002]


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## VW-Kayaker (Apr 5, 2002)

*Re: Understanding N75 (Mr_gimble)*

Edit: never mind someone beat me to it.


[Modified by VW-Kayaker, 10:24 AM 7-30-2002]


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (xray_boy)*

Well, first, the restrictor should be put before the N75 and not after. Just exactly as a restrictor is put in there by default. While the wastegate is air operated, you can make it to open/close slower by restricting the airflow to the wastegate. This is how surging is eliminated. While you are tweaking your N75s to eliminate surging, you are decreasing the boost at the same time. And as you said (wrote) the ECU requests a specified amount and won't be happy with less boost at all. Probably ECU adapts to the new N75 settings, don't know. I wasn't the one who wrote the software.
N75s with stock boost does not really surge (otherwise there's a problem by default). Probably they designed all this system to work surging free at 0.6 bar and not on 1-1.2 bar! I can easily imagine that the magnet/coil in the N75 is really struggling opening/closing all this stuff on 2x as much boost as it is designed to work ok. A smaller restrictor would make N75 to "think" it's still 0.6 bar. Got the point?


[Modified by Sim, 5:36 PM 7-30-2002]


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## SlvrBllt (Oct 15, 2001)

*Re: Understanding N75 (Sim)*

I dont understand how extending the restricted portion of the N75 further up the line will help anything. Wont the pressure seen at the N75 remain the same? And since the N75 is the ECU's only way of reducing/increasing boost, it wont be able to bleed off boost as quickly in the event of detonation or severe overboost. I suppose the ECU could close the throttle thus opening the DV. But the delay between the DV opening and the overboost condition could be harmful. Boost hitting a closed throttle plate and having no where to go (even if just for a fraction of a second) will damage the turbo (compressor surge).


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## cwatson (Jul 29, 2002)

*Re: Understanding N75 (SlvrBllt)*

I think the answer is that, sticking with the control system discussion above, introducing a restriction will add damping to the system. I think they are saying that the boost pressure will still reach the value targeted by the ECU but it will get there more smoothly (less overshoot and oscillation in the control system world). So you aren't actually enhancing performance in terms of the resultant boost. You are instead shaping the response of the closed loop system.


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (SlvrBllt)*

Yes, i understand your concern. The pressure will remain the same after N75, except for slower pressure build up in the wastegate. This will cause a slower turbo shut down, which will cause higher torque (& boost) at low revs but i dont think it would cause any huge spike which would make car to go in to limp mode or whatever (detonation & stuff). ECU will limp if anything is wrong dont worry about that







. All in all, our purpose is to get more power with mods so don't blame me if you'll get a more powerful car at the end







.
"It wont be able to bleed off boost as quickly in the event of detonation or severe overboost."
You got it wrong.
When N75 wents air from wastegate, the turbo WILL boost. Releasing stress off from compressor is the duty of the DV, but it works only when you take your feet off the pedal (so vacuum is available).
BTW regarding to releasing boost by N75; If you don't let much air to enter the N75, the valve itself will have got an easier job releasing boost from the less air even with the default setting (gap). 
Will install a 1mm restrictor into mine soon and we'll find out what happens. I've already had my car working without N75 valve and disabled wastegate. It didn't blow so such a minor mod won't hurt it for sure. Don't worry







.
It's basically the fine tuning of the stock restriction. If you go and think more further, the more restricted N75 on chipped cars will act similar to stock N75s working in unchipped, stock cars.
Unchipped cars = less boost -> slower pressure buildup
Chipped cars = more boost -> faster pressure buildup -> may actually surge.
The N75 valve is a control unit which deals with boosted air. Tuners do generate more boost by chipping, more air, more fuel, more power, but more boost is introduced to N75 too at the same time, which does strange things.
The N75 duty cycle is quite fast... May reach a dozen of switching on/off per second when working OK! But when you feel surging, it hardly can do a single switching in a second.



[Modified by Sim, 11:29 PM 7-30-2002]


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Sim)*

cwatson 
Exactly!


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## [email protected] (Jun 5, 2002)

*Re: Understanding N75 (Sim)*

*AWESOME* post!








This may be a crazy/stupid correlation, but the N75 issues sound similar to the problems many people have with VDO boost gauges. Since the gauges are underdamped, they can buzz and oscillate the needles. The "fix" for that problem is either to install a small filter or a length of hose that creates a larger volume in which pulses may be damped. Maybe those suffering from surging could try lengthening the hose between the N75 and the wastegate.










[Modified by [email protected], 3:06 PM 7-30-2002]


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## deadguy (Apr 13, 2001)

*Re: Understanding N75 (Sim)*

quote:[HR][/HR]maybe some wastegates move a little more freely than others and a binding wastegate arm will cause delays and spikes?[HR][/HR]​That's what I was thinking too, but I suere am glad I got everyone in an uproar over this N75 stuff, glad the topic is back...
And, have you guys ever seens that dawes device or whatever, a really cheap manual boost controller for like 35$, can't remember the link, but it operates the same way as Sim described, except it is not electronic, it even has a small hole about 1.5mm... Anyone seen this or tried it??


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## UKAUSSI (Oct 21, 2001)

*Re: Understanding N75 ([email protected])*

Excellent post & the picture above is excellent.
As most of you know I have done a huge amount of research on the N75/Surging issue. I must have a least 100 or so VAG-COM logs of various UPsolute versions and N75 settings.
I agree that there may be some merit to adding a SLIGHTLY smaller restriction to the pressurized pipe before it enters the N75 as the ECU will change the Duty Cycle on the N75 to compensate for any overboost condition and there may be indeed an inability of the stock N75 to cope with the 100% or so increase in pressure within the pipe.
Below is my graph that shows the ECS N75 & 'C' (OEM) N75. There may be a different diameter pipe inside the N75 as it is slower to react to changes requested by the ECU Duty Cycle. The result is that peak boost is held longer,








My guess is that the connector that goes to the wastegate is narrower on the ECS. This can be seen in the chart below that shows the Duty Cycle % decreased on the ECS N75. Duty Cycle is % of time the N75 opens the valve to vent the air rather than it going to the wastegate. 








I still DO NOT agree with adjusting the N75. If you turn it clockwise you will restrict the ability of the N75 to vent air to the intake causing more air to go to the wastegate and less boost. It is a very subtle adjustment as can be seen by the chart below (done 3 months ago) Because the valve has been screwed downwards the valve cannot open properly to vent the air. Consequently, the ECU has MAX Duty Cycle of 95.3% all the time as it desperately tries to vent air and subsequently increase boost. The more you turn it clockwise the more you restrict the valve and the less boost you get








(Sorry for quick analysis as I am also trying to work, took me an hour to write the above between phone calls for help














)


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## einsig (Jan 29, 2001)

*Re: Understanding N75 (UKAUSSI)*

I have to second everything you have said here, UKAUSSI. I think we have been in agreement since you started the testing of the valves way back when.
The only reason I'm really posting this is to re-iterate that adjusting the N75 screw is A BAD THING. The valves are very fragile and will easily break. More importantly, when you adjust it you are restricting flow in a negative way. Yes you may cure a surge by lowering boost, but you are causing all kinds of whacky stuff to go on with the ECU, duty cycle, wastgate, et al. Please people, don't mess with the screw!


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## jim wilson (Jan 20, 2000)

*Re: Understanding N75 (gintaras)*

quote:[HR][/HR]maybe some wastegates move a little more freely than others and a binding wastegate arm will cause delays and spikes?
That's what I was thinking too, but I suere am glad I got everyone in an uproar over this N75 stuff, glad the topic is back...
And, have you guys ever seens that dawes device or whatever, a really cheap manual boost controller for like 35$, can't remember the link, but it operates the same way as Sim described, except it is not electronic, it even has a small hole about 1.5mm... Anyone seen this or tried it??
[HR][/HR]​Seen it on the WRX forum


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## jim wilson (Jan 20, 2000)

*Re: Understanding N75 (jim wilson)*

perhaps the ECS valve has a larger inlet hole for the boost pressure to enter which lets it react faster so it doesn't over/under shoot the pressure it's trying to get?


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## UKAUSSI (Oct 21, 2001)

*Re: Understanding N75 (jim wilson)*

quote:[HR][/HR]perhaps the ECS valve has a larger inlet hole for the boost pressure to enter which lets it react faster so it doesn't over/under shoot the pressure it's trying to get?[HR][/HR]​But the logs I have done show the opposite. The green line in the middle chart above shows the actual boost slow to come down to specified. Feels GREAT














as you have no spike and lots of mid-range torque http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (UKAUSSI)*

Well, we can agree that adjusting the N75 valve is not a right solution to eliminate surging. As we all know how the N75 works by now, adjusting it counterclockwise will just reduce overall boost even if it helps on the surging issue.
I think the solution will be a restricor (1 to 1.5mm) put before the N75 according to my original plans. I wish i had more time to try this before posting this topic, but i'll get it done tomorrow for sure! Enlarging the inlet of the N75 (as somebody wrote above) will make the situation worser and would result in an immediate drop of boost, as the N75 would not be able to vent enough boost from the increased airflow resulting in an early opened wastegate.
Luckily i do not have got any surging (using C valve), so this mod is only for having a little more initial boost on my 20vt. As as side effect it also may eliminate surging.
PS.: Sorry for mistyping "vent" (went).


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## kevdakaotic (Mar 2, 2001)

*Re: Understanding N75 (Sim)*

who ever comes up with a fix for this will be popular and RICH $$$ !


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## Postman (May 7, 2002)

*Re: Understanding N75 (kevdakaotic)*

I've been reading this thread for a while, especially since I just got chipped with APR 91 Octane on my 337. I have felt the 'un-smoothness' at partial throttle around 4k rpm. This does not feel like compressor surge, but more like a control system problem as *sim* has aluded to. I work with small gas turbine engines running centrifugal compressors and when they surge there is no doubt about it.
I'll call it 'control surging' for lack of a better name. It seems that this could be 'damped' out via means *sim* has suggested using a restrictor. If seen many pneumatic systems where this works. One of my colleagues suggested a small accumulator which would absorb pressure waves. My other thought is couldn't this be fixed in the ECU programming? It's a simple closed loop controller (maybe full PDI) with many damping factors included. If we're all experiencing control surging at partial throttle in a given rpm range why can't we just adjust the control system damping in this range? I would hope the ECU programming could allow for this but since I haven't seen the code I don't know.
Just my $0.02


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Postman)*

I wish we could reprogram our ECU from the scratch. It would be a beast even with stock bits (K03 turbo, etc) though would not last for long thats sure







. Will construct the restrictor this afternoon.


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## Electron Man (Sep 21, 1999)

*Re: Understanding N75 (Sim)*

I'm of the opinion that most of the "dead time" (difference between ECU request for open WG and actual open WG [not instantaneous]) which contributes to surging issues can be blamed on the size/design of the wastegate actuator.
Design of the actuator is a compromise. The "fail closed" actuator needs to have a spring large enough to keep the wastegate closed (F=kx; k affected by coil and wire diameter), yet small enough so that it doesn't take too long (build-up of pressure inside actuator takes time-depends on actuator volume) to open the wastegate. Take too long to open the actuator, and max. allowable boost is exceeded.
It's not what your ultimate boost is, but rather how fast you reach it...and how quickly the actuator (working in conjunction with N75) can limit the rate of boost increase.
Get a less restrictive exhaust system and it becomes more critical to have less dead time so you can avoid high boost build rates (such that ECU can't close the wastegate fast enough).
Good discussion.










[Modified by Electron Man, 7:47 AM 7-31-2002]


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## vwgreek (Jan 24, 2002)

*Re: Understanding N75 (Electron Man)*

What about this "Dawes Device"? Anyone know anything about it beyone what little has been said already?
Great thread! There should be a separate section for these great threads.


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## deadguy (Apr 13, 2001)

*Re: Understanding N75 (vwgreek)*

I wonder if we can ditch the N75 for one of these
http://home.austin.rr.com/gabedude/boost.html 
or these
http://www.dawesdevices.com/


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## deadguy (Apr 13, 2001)

*Re: Understanding N75 (gintaras)*

especially this one though > http://www.dawesdevices.com/


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (gintaras)*

Well, dawesdevices and the like should actually be really nice (especially if you consider the price tag).
As the part of my N75 experiments i had lots of time dealt with the wastegate itself and running the car N75 less. I don't really suggest this, though you may try it for 1-2 laps it shouldn't do any damage to your engine.
I just simply closed the line going to the wastegate from the N75. I unplugged the hose, clogged it with a screw, put a suitable sized hose on the N75 too (from where i unhooked wastegate) and clogged it too, tightly. With this setup i prevented the turbo to open its wastegate. With stock K03 it should be safe with all hoses & stock IC, there won't be such a big pressure which could blow the engine or anything. I got 1.3 bar at lower revs and 1 bar sustained thru the rev range. Guess how fast my car was, if actually not spinning its wheels







.
I did this test to verify my turbo is not blown by default, because i had a problem (later turned out that it was N75 related) which prevented my boost to go higher than 0.68-0.7 bar. Using the car this way (with unleashed potentials) proven me that ECU and N75 is HOLDING the car back big time - even when chipped. Ok, you may say we should keep a safety margin, otherwise the turbo & engine will be short lifed. That's sure - i wont argue, BUT i mean all those flat spots, hesitations (incl. surging) ECU & N75 produces will be quite unacceptable after having driven a car without these things.
Dawesdevice and all shorts of stuff usually requires to omit/skip the N75 which is the only way for the ECU to control boost. You will have a LOT more smoother torque curve and a LOT more impressive car, BUT you will possibly lose ESP/ASR/TCS whatever you call it.
Then there is a very important thing on which you have to take care. The air/fuel ratio. If you tweak the boost way up, you will be running too lean which will result in overheating - in most extreme cases, molten pistons. Therefore, do not ever try to disable the N75 (the way i described or any other way) on stock, unchipped cars. It is said that the standard fuel map is safe up till 1.0 bar of boost, but anything above and you'll be running dangerously lean!!!


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## john s (Nov 14, 2000)

Nice set of posts.
>>>It can modulate the frequency going to the N75…
No frequency is constant, duty cycle changes.
>>>does anyone know the insides of the ECU? what logic it is using? what kind of controller 
Infineon C167 superscaler 16-bit microcontroller. Infineon website shows programing example using CAPCOM register to implement fuel injection. Couple of old posts on ECU control in gereral:
http://forums.audiworld.com/tt/msgs/365279.phtml
http://forums.audiworld.com/tt/msgs/111898.phtml
>>>(in college we just used the very basic old 8088 processors)
I thought the 4004 was old, you saying I'm old?
>>>Probably ECU adapts to the new N75 settings, don't know. 
Yes, you can monitor it on block #119, item #2.
>>>it wont be able to bleed off boost as quickly in the event of detonation 
First line of attack is retarding ignition timing, then enriching fuel, then reducing boost, then restricting rpm range, finally restricting throttle movement. Fuel enrichment is also done preemptively. The first 3 actions are considered normal, the latter 2 are fault conditions.
>>>Please people, don't mess with the screw!
The adjustment is for part assembly, doing so for surge control is a hack.


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (john s)*

So, finally i have made the restrictor and installed it!!!
Sadly i have no VAG-COM or anything which i could monitor the changes with, i just have to rely on my feelings which as we know are quite inaccurate. Then, just as i got ready the rain begun to fall







(( and the temperature dropped 10 C degrees too, so it will not be a secret if i tell you that my wheels spun like hell!
Hesitations are still there (maybe its time to grease my forge), turbo spin did not get more agressive at all, but a convincing amount of extra low down torque has been acquired for sure. As the engine revs 4000-4500, torque begins to fall just as with the default gap. It seems that my aim has been accomplished: the wastegate with the restriction opens later.
I have checked the stock hole on the N75 is around 1.7-1.8mm. I took a 8mm, 3cm long alu rod, begun with 4mm drill bit from both sides. Drilled in 12mm deep then took an 1mm drill bit and drilled thru completely. As i blew thru it, it was way too restrictive, so i continued drilling (moving 1mm drill bit sideways) until the hole got around 1.3mm wide. Installed it before the N75.
It was just a short test (max 1km), mainly flooring the car. No CEL or limping yet.
"Sadly" i can't say that "wow it eliminated surging" as my car wasnt surging with the stock restriction either. I will test the thing more furthen in the following weeks in different kind of situations (urban driving/motorway/etc..)
Any other brave venturesome (with VAG-COM) who would also try it???


[Modified by Sim, 8:15 PM 7-31-2002]


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## Prodigy (Jul 16, 2002)

*Re: Understanding N75 (vwgreek)*

Here's a diagram of the N75 valve for you guys...I have some thoughts on this subject as well but I'll post those later


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## UKAUSSI (Oct 21, 2001)

*Re: Understanding N75 (Prodigy)*

If you disconnect/block the pressurised pipe from the N75 to the wastegate what cause the wastegate to open ?
I am making an assumption that it is opening based on the boost being limited to 1.3bar max and 1Bar at high rpm with the pipe disconnected/blocked.
Finally, what IS 1.3bar when we measure it onthe VAG-COM. Block115 on my car (see sig) shows max 2350mbar Actual boost dropping to 1850 at 6000rpm with the N75 connected ?!


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (UKAUSSI)*

UKAUSSI,
Yes, i also think that the wastegate opens at ~1.3 bar by itself (mines a 150BHP K03 20vt) (my max 1.3bar may not be accurate however). Maybe the exhaust pressure forcing it from the other side (or is that b.ulls.hit?) - really no idea!!! At high rpms, it just cannot deliver that much air the quickly moving pistons would need so overall boost drops.
If you are measuring boost via the ECU, you have to subtract 1000 mbar from all the values. 1000mbar is the atmospheric pressure, if it shows a smaller value than 1000mbar then it is negative pressure. Then, you just have to divide the value with 1000 to get it in bar. So 2350mbar = 1.35Bar, 1850=0.85Bar.
***
I gave the car another run just before - drove to have some dinner around and diagnosed some problems with the 1.3mm restriction.
I think the 1.3mm restriction is way too restricted! It seems that ECU doesn't really have any control on the wastegate now below ~3500RPM. It is very impressive, car pulls like mad, BUT as the needed pressure builds up in the wastegate to open it, it will immediately open! Probably ECU already wanting to lower the boost pressure (as it should be a lot higher than requested), but couldn't do it because there is no pressure in the N75 yet. This causes a flat spot around 3500-4000 RPM, since ECU will immediately open the wastegate. After ECU regained control over the wastegate, everything is fine again (above ~4000-4500 RPM). Though this this flat spot is not there always, but it has to be eliminated! I will buy a 1.5mm drill bit tomorrow and enlarge the restriction (remember, stock is 1.8mm). The 0.2mm (from 1.3 to 1.5) difference may not be significant in diameter, but it IS in airflow!


[Modified by Sim, 10:16 PM 7-31-2002]


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## Postman (May 7, 2002)

*Re: Understanding N75 (UKAUSSI)*

quote:[HR][/HR]Finally, what IS 1.3bar when we measure it onthe VAG-COM. Block115 on my car (see sig) shows max 2350mbar Actual boost dropping to 1850 at 6000rpm with the N75 connected ?![HR][/HR]​That sounds just fine. Sea level is 1000 mbar, or 1bar. The values the VAG gives are in absolute mbar. So 2350 is actually 1350 mbag gauge (above atmospheric, which is usually really close to 1000 mbar). Which means 1.35bar, or 19.7 psig (1 bar = 14.7 psi, throw the g on for gauge).


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## Postman (May 7, 2002)

*Re: Understanding N75 (Sim)*

Sim, I have been reading over your testing a lot and have discussed this issue quote a bit with my aero buddies here at work (we make small gas turbine engines with the same style compressors as our 1.8T's).
I also experience this flat/unstable feeling between 3500-4000 rpm at 1/2 throttle on my chipped 337. You claim it goes away above 4000 rpm after the ECU regains control. So this sounds like a small compressor instability at that point. This also happens to be the point where the N75 starts to open as the compressor has reached the boost required by the ECU. Restricting the line to the N75 valve will cause your turbo to run( spike) higher boost than needed and may eventually wear it out. Restricting the bypass line of the N75 will also cause higher boost and is the same as turning the screw on the valve, a no-no.
We're all trying to get the instability from occurring so no flat spot or unsteadiness. My friend thinks the instability comes when the N75 opens and there is now a flow disturbance on the inlet of the compressor which pushes it close to surge. He has experienced this on larger gas turbine engines. Our conclusion was to put an accumulator-type device in the return line coming off the N75. This will damp any waves (shock-wavesactually) and not 'disturb the inlet flow on the compressor. It would need to have a bit of volume and some baffles, almost like a muffler (and we all know what those do to noise/pressure waves). I was thinking of a fuel filter or something at least a cup in size or so.
Anyone want to try this? *Sim*, I know you're been trying a lot of things, could you rig this up?


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## NJWolf18T (Jan 18, 2002)

*Re: Understanding N75 (Sim)*

thanks for all the info man


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Postman)*

Postman,
your idea with the fuel filter to the return line of the N75 sounds interesting. Though depending on my experiments with the N75, its return line is extremely restricted, even with the leftmost N75 screw position. The N75 itself is way restricted (with 1.8mm on "C" valve) too, and when N75 gets opened, the return line will be "double restricted". Once by the stock restriction before N75, then by the piston inside N75 (the gap inside should be smaller than the restriction hole of the N75). With my setup it's three times restricted. Then at the other side of the return line, theres vacuum, so it will suck the air thru the filter and suck everything out from the line going to the wastegate (also a little bit from the IC & combustion chambers thru the N75's restriction).
One thing is sure, 1.3mm is too narrow so i will try the 1.5, max 1.6mm today. If the flat spot will be still there i'll experiment more further (even with the return line).


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## Sim (Jun 27, 2002)

*Re: Understanding N75 (Sim)*

have installed the 1.5mm restrictor. I kept the 1.3mm one (which after a closed inspection turned out that is only a ~1.2 mm one) because the car was damn fast with it, will put it back for my next 0-60, 1/4 mile run.
So, lots of changes with the 1.5mm one. The car behaves just like with no extra restriction (like with stock N75 setup: no serious turbo overshots/sudden boost drops) except for bigger low/mid torque around 3000-3500 RPM. I think it should be similar to the ECS N75 valve. Not quite good for high RPMs, but gives a decent amount of extra power for urban driving - coming very handy!
A flat spot is still there, but not always and i am beginning to suspect it is caused by my DV or anything else as it was already there with the stock N75 setup, too. Still no CEL or limping.
It would be nice if anybody else could try the 1.5mm restriction who HAS surging to check if it eliminates it or not.
Will post about how i did my restrictor later on.


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## Cypher2k (Nov 23, 2000)

*Re: Understanding N75 (Sim)*

An inline fuel filter might make a dandy air baffle. I know they use em on boost guages to smooth them out and eliminate buzzing.


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## UKAUSSI (Oct 21, 2001)

*Re: Understanding N75 (Cypher2k)*

Any updates ?? 
Now I am no longer confined to house (sick) I am ready for some more testing










[Modified by UKAUSSI, 7:10 PM 8-9-2002]


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## Al Bob (May 23, 2001)

*Re: Understanding N75 (UKAUSSI)*

Uhh, I don't have alot of experience with controlled duty cycles and lag time in these type of controllers, but how about this:
From what I can see, there is a spring in the wastegate that compresses under pressure. The pressure that this spring sees will be higher under larger boost pressures. Get above stock boost levels and the spring will stay compressed. It seems that increasing the spring rate and then reducing the restrictions of the N75 and related air lines would allow the entire assembly to react better to the higher boost rates.


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## DimcheMKV (Jan 13, 2002)

*Re: Understanding N75 (Al Bob)*

How bout clamping the vacume line instead of adding a restrictor??? Will this do the same???
My Gfs brother was telling me to clamp a vacume hose, i think to the wastgate, he siad it will upboost....Im very willing to try this if its safe and all and wont cause any problems to the car?????No Vagcom, or boost gauge so i cant really tell what will be going on, all i can do is a BUTT dyno








But if its possible to just clamp a vacume line and it will creat more low end power and not effect top end power, then someone tell me how to do this!!!!!!!


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## smashbox (Jun 17, 2001)

*sim*

bump
great topic http://****************.com/smile/emthup.gif 
i tried the links from your first post and got redirected to an updated forum, but i could not find the specific threads you linked to.
if you could repost the links that would be great
thanks








scott


[Modified by blu1552, 4:30 AM 8-22-2002]


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## Sim (Jun 27, 2002)

*Re: sim (blu1552)*

Huh, you want update ehh?
Well we have tested restricting the air entering into the n75 with an 1.5mm restrictor. The stock restriction (depending on your measurements) is 1.65mm in the N75 valve. Three cars have been tested, 1x stock (minor torque increase below 3500), 1x 1.1 bar chipped - same symptoms but a bit higher torque increase below 3500 and 1x 1.3 bar chipped with just a minor (very very small) improvement. We believe that the 1.3 bar one was already running near to the maximum, so not much space for improvement were there.
It seems that the turbo can spool up more freely with a higher restriction as the N75 valve doesn't have enough pressure built-up to have control over the wastegate. At 3500, there is an ovbious and sudden drop of boost (as N75 regains control), but the increased low down torque comes very handy in urban driving. 1.2mm has been also tested, N75 didn't have a chance to "access" wastegate below 4500. I have shimmed my forge too (5mm) and a few extra boost is available at higher RPMs - not sure it's because of the restriction.


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## smashbox (Jun 17, 2001)

*Re: sim (Sim)*

http://****************.com/smile/emthup.gif 
thanks
scott


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## 1.8T Jon (Jun 24, 2001)

*Re: sim (blu1552)*

Great Post. One of the most informative I have read. Any further results. I have surging in my AWW Jetta and am looking for the cure. I am considering the "C" version of the N75, but I like the idea of a "reservoir" before the N75.
Any ideas or comments.
TTT


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## Sim (Jun 27, 2002)

*Re: sim (1.8T Jon)*

Try it then post the results


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## UKAUSSI (Oct 21, 2001)

*Re: sim (Sim)*

Pulled out my broken 'F' version N75 and compared it to the ECS version I have.
I was VERY SURPRISED to see that the intake pipe had a much smaller restriction on the 'F' version







It was just a little bigger than 1/16" (tested using drill bit) with the ECS being double at approx 1/8".
Also, the exit pipe to the wastegate had NO RESTRICTION on the ECS version but had a slight (forgot to measure) restriction on the 'F' version.
Hmm...







Quite the opposite of what I was expecting. 
I would have liked to start testing restrictions with my 'F' but it was only giving me max 1350mbar (5psi) and duty cycle of max 95.3% so definitely broken


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## Sim (Jun 27, 2002)

*Re: sim (UKAUSSI)*

Yes thats possibly broken.
Sadly theres no way we could enlarge the hole in a stock N75, because all the swarf & dirt would go inside and damage the thing i think. Maybe with a hot wire - dunno.
In addition to our N75 restriction tests;
No CEL, no limping, BUT: maximum boost pressure exceeded limit (or something like that) message from the ECU, i also got maximum RPM limit exceeded too


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (Sim)*

Hi! I did all the testing found in this thread and came to the conclusion to fit a dawes device in the pressure line before the N75. It's very easy to install and to adjust and I get very good results with my TT. I stay just under 1,5bar in overboost and everything is fine. From about 5000rpm the N75 takes over again and controls the boost in the higher rpms. So, with a configuration like that you have the best out of both worlds.
http://loevenich.bei.t-online.de/LD0409.jpg 
http://loevenich.bei.t-online.de/NMPS0409.jpg


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## nremme (Oct 22, 2001)

*Re: sim (CarfanaTTic)*

Do you have any install pics??


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (nremme)*

Will do some pics tomorrow.


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## gtimenace (Jul 27, 2002)

*Re: sim (CarfanaTTic)*

WOW!!!! This is getting good! It's like one of those spanish sopoperas!! I can't wait to see what happens next!!!!!


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (CarfanaTTic)*

Here are the pics:
http://loevenich.bei.t-online.de/DD.jpg 
http://loevenich.bei.t-online.de/DD1.jpg 
http://loevenich.bei.t-online.de/DD2.jpg


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## UKAUSSI (Oct 21, 2001)

*Re: sim (CarfanaTTic)*



























[Modified by UKAUSSI, 9:01 AM 9-8-2002]


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## MoBlueTT (Aug 17, 2002)

*Re: sim (UKAUSSI)*

In the spirit of Clarification (or perhaps confusion)... look at this discussion of Anti-wastegate creep ...
http://www.autospeed.com/A_0670/page1.html
http://www.autospeed.com/A_0685/page1.html
IF I'm reading the discussion correctly, the Variable pressure regulators are doing what the "fixed" restrictors are doing...










[Modified by MoBlueTT, 8:57 PM 9-8-2002]


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (MoBlueTT)*

That's right, but the point is variable adjustment. Thats why the DD is much better.


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## 16vracer (Jul 12, 1999)

*Re: sim (CarfanaTTic)*

Is anyone using the ECS N75 Race valve with an APR stg3 kit?


[Modified by 16vracer, 12:00 PM 9-14-2002]


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## Sim (Jun 27, 2002)

*Re: sim (16vracer)*

I think most of the chipped people use the stock n75 valve.


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## Speedy G (Apr 1, 2002)

*Re: sim (Sim)*

Guys, from the posts I've seen, I see some confusion between surge and the N75 valve. Surge is due to the the wastegate overshooting the desired boost level that the ECU requests. The wastegate actually averages out the output of the N75 to produce a smooth boost curve that actually goes to the engine (although the curve out of the N75 is NOT smooth). I have some experience in control systems. The two overshooting scenarios:
1) The wastegate opens too much -> lets too much boost out -> ECU closes wastegate (using N75) which leads to #2.
2) Wastegate closes too much -> increases boost too much -> ECU opens wastegate (using N75) which leads to #1... and so on.
Why does this happen? It's an unstable control loop. You can do several things in this case:
1) The sampling rate of boost by the ECU may be too slow and therefore it's too slow at correcting the error in boost (can't do, maybe programmers can but we sure can't).
2) Add some dampening in software to correct for this, this is called proper software development (we can't do again). So why don't the tuners do this properly you ask? Do they just suck? No! Car control systems are pretty much the biggest nightmare in control systems, since mechanical tolerances vary, but the software's the same. This means the software is supposed to control a variety of systems, which calls for adaptive control, which is just tough stuff. The adaptive control part is why the surging may reappear after a week if the N75 is adjusted.
3) This is what we can do as car hackers. We can dampen the mechanical system so that it reacts like the ECU expects. The added boost coming out of the N75 makes the wastegate open and close too quickly, so we can do two things:
a) Reduce the boost coming out of the N75 valve so the rate of adjustment of the wastegate lowers. I guess people tried doing this by inserting the restriction. This won't do it because you're not adjusting the boost, you're just adjusting the rate at which the boost changes in the wastegate, which is not the same. You'll still surge in 3rd gear when boost is to be maintained at a certain level for a long period of time. You'd need a boost controller to lower the 16psi back down to 6psi (duh!! a boost controller for the boost controller...) Although this boost controller for the boost controller works, it's highly impractical $$$-wise.
b) Stiffen the spring in the wastegate to slow it down. I'm not sure how practical this is, but this really is the only solution I see that will work adjusting mechanical variables.
Cheers,
Speedy G


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (Speedy G)*

You are definatly right, but you can't change the spring in our wastegate actuators. So you have to buy a new one which is much more expensive than a Dawes Device. The result is the same with a DD and that is what counts for me.The next point is that I keep all the security options the ECU gives me (boost cut)with my configuration because the N75 can open the line to the Wastegate completely.


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## Speedy G (Apr 1, 2002)

*Re: sim (CarfanaTTic)*

Hmmm, no spring... Well then, back to my a possibility... 
You can reduce the boost after the N75 valve that drives the wastegate. As I said, a boost controller for the boost controller. You plug the output of the N75 to the DD then to the wastegate. Set the max boost after the DD lower than engine boost so the wastegate gets less boost. The excess boost will go to the atmosphere. This way you still have the N75 controlling the engine boost, but you set a lower boost level to drive the wastegate so it doesn't overshoot the ECU command.
Anybody want to try? I guess the $35 part is worth it.
Speedy G


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## Speedy G (Apr 1, 2002)

*Re: sim (Speedy G)*

It might not work (for a long time) if the opening and closing of the N75 adversely affects the DD. How does the DD work?
Speedy G


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (Speedy G)*

You can set the opening point on the DD. If you set it to 1bar it will stay shut until you reach that pressure and than holds it. You can fit it between the N75 and the wategate but than you will lose all security options. If you will go this way you can also use it without the N75. Would be the same.


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## Speedy G (Apr 1, 2002)

*Re: sim (Speedy G)*

The only other logical solution that I see is to put a bleeder between the N75 and wastegate. The DD is not a bleeder valve (just read their spec). The bleeder valve may actually be cheaper than the DD and work better.
Yeah, I vote for the bleeder valve after the N75 and the wastegate. http://****************.com/smile/emthup.gif 
Speedy G


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## Speedy G (Apr 1, 2002)

*Re: sim (Speedy G)*

Actually with regards to your explanation on the DD, it wouldn't work between the N75 and the wastegate, since it doesn't work like I thought it would. The ideal is a valve that let's boost get to the wastegate UNTIL a certain boost point is reached. The excess boost should be bled to the atmosphere. This will provide you with full ECU control over the wastegate, AND the fastest possible wastegate activation.
Speedy G


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (Speedy G)*

I wouln't use a bleeder valve because you get boost spikes with them and no constant boost.


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## Speedy G (Apr 1, 2002)

*Re: sim (CarfanaTTic)*

Nah, not in this way. Bleeder valves are usually used instead of the N75 valve, just like the DD is used to replace the N75 and ECU wastegate control. What I'm saying is to lower the boost leaving the N75 and into the wastegate. It's essentially the same thing as stiffening the spring in the wastegate. Instead of adding force to the spring, I'm lessening the force pushing on the spring. That's the idea. A bleeder valve will cost you 20 bucks (or Euros, actually prices in Europe are x3 so 60 Euros), and the worse thing that can happen is that the wastegate stays fully open, so no boost. You can't break anything. Remember, the point is the bleeder valve is AFTER the N75 boost regulator.
Speedy G


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## Speedy G (Apr 1, 2002)

*Re: sim (Speedy G)*

BTW good luck to the Schumis tomorrow, although I think Montoya will finally win...
Servas from Colombia
Speedy G


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## Speedy G (Apr 1, 2002)

*Re: sim (Speedy G)*

Hey this bleeder after N75 idea might actually give off a strage sound, I might give it a try even if I don't have surging, just to see how it sounds.
Speedy G


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## CarfanaTTic (Aug 24, 2002)

*Re: sim (Speedy G)*

With a bleed you will rise the boost from low to high rpm's. Thats not what I want with a chiped car. I wanted high boost in the low and middle rpm's and no rise in boost in the high rpm's. That is what I want and get with the DD.
B.T.W.: The Euro and Dollar are nearly 1:1


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## Speedy G (Apr 1, 2002)

*Re: sim (CarfanaTTic)*

Again, not the way I'm saying you should install it. In this way, the N75 controls engine boost. The bleeder is just slowing down the wastegate so it doesn't overshoot.
Also Euro







ollar is 1:1 but in my experience prices are 3:1 for vw parts, just compare APR UK vs APR US prices.








Speedy G


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## Varooom (Aug 5, 1999)

*Re: sim (Sim)*

Been reading alot about the N75, hoping to cure the massive surging my awd (with n75c and apr) began having recently.
Sim and others, your posts are especially informative and interesting.
I've got a few thoughts:
If the highoutput version of the TT, and the new 180hp 1.8t also use n75 controlers, wouldn't that mean there's one out there that's designed to handle the extra boost?
My car functioned well for about 40,000 miles, always in chip mode. Only recently has the surging begun. This tells me the n75, or whatever part of the system that is now malfunctioning was, for a long time, working adequately. So, something has degraded rather than something being intrinsically unable.
I wonder about this whole version "f" and version "c" thing. Mine is a "c" and the surging is so bad the car can't be driven in chip mode. 
It's so difficult to interpret what's happening, it's nothing approaching imperical evidence. It could be that thousand more are buying 1.8t's and chipping them and showing up here since the "f" n75 went into production.
This would make it look like the "f" is bad and the "C" is less bad.

Anyhow, I'd just like my car to work the way it used to. I hope I get there soon.


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## Sim (Jun 27, 2002)

*Re: sim (Varooom)*

well, good luck. I think you may try a new N75 valve however. If it makes any change then this stuff is probably connected to the N75 valve.


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## TheMel (Mar 28, 2012)

:thumbup: Bump for damn good info and an informative debate. :thumbup:


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## Cryser (Sep 9, 2009)

TheMel said:


> :thumbup: Bump for damn good info and an informative debate. :thumbup:


you really bumped a 10 year old thread....


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## TheMel (Mar 28, 2012)

Cryser said:


> you really bumped a 10 year old thread....


I've been having a similar issue. So yeah. Why's that so bad?

Unless you like answering repeated questions from people who don't know how to use the search button...


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## iyreluctantly (Sep 25, 2015)

How much do you turn the adjuster screw?

Sent from my GT-I9505 using Tapatalk


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## AmIdYfReAk (Nov 8, 2006)

This is officially the necromancer thread!! It'll never stay dead!!! Ahhhhh!!


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## Jennifer_a (Nov 19, 2013)

No i believe it won't 
I too have been suspecting for years the N75 had something to do with the weak boost and lowend weak power for urban driving and was also contemplating a restrictor or valve to let air escape and was very surprised finding this discussion discussing restrictors as well as valves letting some of the air escape. I had the exact same ideas and found this discussion very interesting 
Anyway, the other day I found a discussion on another forum about the N75 where they mentioned the adjustment screw on the N75. I was surprised to read the N75 has an adjustment screw. I went to look and there it was 
I knew my problem was solved!
I first adjusted the screw half a turn counter clockwise as mentioned to let the wastegate open later. It made a difference but not much however this inspired me to push forward and turn it another half turn. Now I could feel a definite improvement in urban driving - more lowend power. I gave the N75 another half turn and now my vehicle really felt great on lowend for urban driving.
I had to go to another town for business and vehicle definitely feels much better when starting to boost on highway than before.
I am satisfied with the performance on preboost and during boost. I'll leave the N75 on 1.5 turns.
I checked sparkplugs and mixture was too lean and added a 1% enrichment value with Unisettings.
Engine feels great with extra lowend power and extra boost.
Please don't curse me for replying to an old discussion, I just want to share my success story.


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## Senior Member (Jul 2, 2016)

The good old N75


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