View Full Version : Cheap N75 mod for everybody
As some of you already know, i am deeply into N75 valve investigating & experimenting lately. Here's a new & easy DIY mod which will work for anybody (with chipped or unchipped car) and doesn't really need any major modifications on the car which couldn't be reverted ANY time in just 5 minutes.
This mod involves a bit of "fine tuning" on the stock N75 valve. No, it is not screw adjustment, not replacement, just a little trick. Gains are favourably noticable which makes both chipped and unchipped cars to have more low/mid torque (poor clutch ;)).
The basics in a nutshell
As you already know the wastegate on our turbos is air operated. ECU directs air to the wastegate (using the N75 valve) to open/close the wastegate when needed. The hose delivering boost to the N75 valve is 8mm in diameter, but it doesn't use all that much air to operate the wastegate, there is a 1.8mm restriction before (actually in) the stock ("C") N75 valve.
The trick
What we do with this trick is to restrict the air entering the N75 a little more further, which will cause the wastegate to open a bit later at low revs, sustaining the charasteristic inital 20VT boost spike a bit more further. This will result in a more massive pull until around 3500 RPM, which comes very extremely handy in urban driving (otherwise everything is the same). This trick will act similarly to an aftermarket "race" N75 valve, besides contributing to eliminate possible surging.
Yield if anyone wants to try (no CEL, no limping), i can arrange an article in no time.
Here are some pictures;
Please make an article out of it... I wouild like to do it myself, but don't want to "screw" my n75 heh and please with clear pics. As I still don't really get what the n75 exactly is in the engine bay.
Thanks in advance,
Alf
Heh, dont worry. You can't really "screw" your N75 (neither anything else), you doesn't even have to touch it (except for removing stock pipe).
Shock_Xe
02-08-2002, 11:41
Agree with alf do an artcile, also i aint got a clue what/where n75 valve is so would be nice to have arrows on piccys!!!! And show what the tube looks like off with that bitty thing in!!! cheers
See attached...
The N75 is correct - I'm guessing with the restrictor.
Sim - could this be done with an in-line tap providing adjustment.
Poo.. see below forr attachment
Shock_Xe
02-08-2002, 13:54
So what did you do?? just put 2 jubilee clips on????
So, i had lots of fun with the car today. Quite hot weahter again (33C) and with AC running the car still felt faster than with no restriction (no AC) in cold weather. If you knew how much actually got my car from me ;), i'm beginning to think that i'll fall apart sooner or later in the case i don't "get the figure lighter" :D. Not mentioning fuel consumption...
Anyway, i think it would be too early to compose an article out of this mod as i still don't have got any dyno plots (probably i won't even have as RRs are expensive here) or VAG-COM test. By the way, i will give you all the necessary info and hints to make & install such a restrictor, and it would be nice if you (anybody) could verify the results with VAG-COM datalogging.
The performance gains are impressive! So much, that i am a little bit concerned about suggesting this mod for chipped cars. I got a 1.1 bar chip, but it feels a LOT faster than that with the restrictor in - i can easily imagine that my boost now hits the 1.3 bar (19 psi) below 3500rpm and i think that's a bit much for my little K03 (and clutch). Stock cars also should gain about +0.2 bar, but it will be still below 1 bar so no problems (neither with stock fuel mapping which is said should be safe up till 1 bar).
So here comes how to make the restrictor:
The restrictor
Shopping list;
From hardware store:
- Get a piece of 8mm diameter solid aluminum rod. I got 1 meter (that was the smallest they sell), you'll need ~3 cm for a restrictor.
- Get 1.5mm drill bits. You also will need a 5mm drill bit (may be 4mm) and a bigger one too, lets say 6 mm. 3 drill bits overall.
- Get sanding papers, a rough one 100 grit, and a very fine 800 or 1000 grit.
From auto parts store:
- 8mm strong fuel hose (1 meter) and four suitable small clamps/clips.
From supermarket:
- Get simple ear cleaning sticks (which have cotton on both sides).
!!!You will need to have a drilling machine a saw and a vice to accomplish the task!!! If you don't have any of these, get or borrow.
1. Cut a length of 3cm off the alu rod.
2. Grip it in the vice vertically.
3. Start with the 5mm (or 4mm) drilling bit, and try to drill a hole in ~12mm deep vertically in the middle. Don't worry if it's not 100 vertical or in the middle.
4. Then turn the "restrictor" around and do the same from the other side too.
Remark: you may grip the "restrictor" tightly, it may do some stratches/damage on the outside (as alu is soft), no problem it will make the restrictor a rougher outside, easy for the clips to hold in the hose.
5. Now drill the small 1.5mm hole in too, completely through. Be careful not to crack that small and fragile bit.
6. Now use the biggest drill bit (6mm) and make a nice rim for the 5mm (or 4mm) hole on both sides. Don't drill in with the 6mm bit, just smoothen the edge, making a rim!
There you go: your restrictor is ready, however it is still not ready for use! It is probably full with alu filings and swarf which has to be totally eliminated.
7. Grip the 8mm restrictor into the drilling machine (like if it would be a drilling bit). Since it is only 3cm long, you cant put it deeply in, make sure it is safe & tight but still sticks out of the chuck.
8. Turn the drilling machine on and rub the restrictor against the rough sanding paper to smooth the edges (so the restrictor is not sharp doing damage to the hose) and top.
9. To "polish" the inside of the restrictor, take a tiny piece of extremely soft sanding paper and wrap an ear stick with it. Put it inside the restrictor and turn the drilling machine on, while holding the stick tightly (now the 5mm drilling bit comes handy as the hole will be larger to put all this stuff inside). This will remove any filings which may left inside. Do it from both sides and for all edges and wherever you want. It will give a nice smooth finish to the inside of the restrictor. Sadly you cannot polish the 1.5mm section as there's no way you could put anything inside, but if you have used a new and sharp drilling bit(s), there won't be any filings in it.
10. After you have polished the inside, repeat step 9 with just a simple ear cleaning stick (with no fine sanding paper on it). This will remove the dark fine alu dust.
11. Double check again for any aluminum filings, NOTHING should be in the restrictor, otherwise it may enter the engine itself. Blow in the stuff several times, or try to force water through it. I used the 8mm fuel hose to do this. I secured the restrictor in the hose, and let water in it from the tap.
You can find a "theoretic" diagram of the restrictor below. It's not a problem if it's not that perfect (it won't be, unless using a lathe), just be sure it is something like that.
Also the diameter of the restriction is absolutely critical! The stock restriction in the N75 is 1.8mm. I've tried a 1.2mm one, but it hardly gave ECU any chance to have control over wastegate, so do not go below 1.5mm!!! 1.5mm is OK.
How to install
As you could see on the previous attachments, the restrictor should be installed between the big alu pipe on the top of the 20vt engine and the N75.
1. Get the stock pipe off, which will be a hard job due to those sh*t stock clamps. Don't even try to touch those, they wont come off, you'll just damage them. Use a big flat head screwdriver, and try to lift the stock pipe with clamp on it from the big alu pipe going down to the IC. It probably will come off (as it did for me too). Then try the same at the N75 too, just be careful, don't break it. Put the stock piping with the clamps on it away.
2. Measure the appropriate amount of 8mm fuel hose (it's hardly 20cm on ibizas).
3. Cut it ca. 5-7cm from the N75 side and insert the restrictor. Secure it with clamps/clips. Don't worry engine or N75 wont suck it thorugh the fuel hose ;).
4. Finish the installation by securing all clamps. Watch out if the metal clamps don't rub on any rubber hose (they may!). Also the "aftermarket" fuel hose will allocate more space than the stock bent one. I'm not sure if it will touch the engine cover as i'm not using it (i hope you can get it off btw ;).
Well, i think that's all.
I'm curiously waiting for the results especially on stock (unchipped) cars. For me it's OK, no CEL, no limp mode. A slightly higher fuel consumption, but i can't resist flooring it now. Be careful with your turbo though! Let it to cool down properly before shutting down engine!!!
sportbilly
02-08-2002, 16:23
Something for the weekend ....
If anyone gets this done easily then you may want to think about making a few extra ... catch my drift !!!
This sounds very tempting - but also slightly risky as it seems to simple not to have any drawbacks. I would be interested to hear what some of the chip tuning companies make of this.
The more i'm having this restrictor on my chipped car, the more i am conderned about the turbo. If you thought your 1.0-1.1 bar chipped car is fast, then you were wrong!!!
I will possibly contraindicate this mod for permanent use in chipped cars. This could be however be a very cheap and easily revertable mod for standard cars, for the one who wants a little more boost without installing a manual boost controller.
The problem is, that chipped cars are already running near to the maximum which is still safe for the turbo (~1 bar). Using this restrictor, you may easily exceed this threshold limit and i bet noone wants an early turbo swap. The car is really fabulous and fast with it, but may be close to its limits. Be warned!
With cars running on stock chip, the turbo will not be able to boost up till dangerous levels, so no such problems like with the chipped cars. I'm not saying it does not worth a try. On the contrary! Learn how your fast your car actually can be, but i'm not suggesting it for permanent use on chipped cars.
You may fine tune the restrictor however to fit your needs and chipped car (enlarge the restriction from 1.5mm up till 1.8mm). I will prepare more restricors (with different gaps) and keep them for strictly "track day" use.
Sim,
Dont worry about running 19psi boost, i have been running an upsolute V2 1.3bar chip for the last 50,000 miles at 21-22psi !! (verified with my boost gauge and vag-com), absolutely no problems with it at all, my car has now done 80,000 miles in total and no engine or turbo problems at all,
Although i had an 'F' N75 fitted 3 weks ago and this can surge somtimes in mid range acceleration,
Have you found out what the difference is between the good 'C' version and the bad 'F' version of N75 ?
come on then who has got a lathe that can produce these things it will be interesting what the results will be like after data loging with vagcom.
Shock_Xe
03-08-2002, 09:10
Actually my uncle has a laith as he has just started up a business!!!!!
Well, the restrictor may not be 100% perfect and symmetrical, so a lathe is not essintial at all. Using one would result in nice looking products, but as for operation i suppose they would be just the same.
Mosser,
if you got surging, then you would be a perfect "victim" to give a restrictor a try. Since you are already running on high boost (i thought 1.3bar is the limit), i'd suggest you use a bigger gap (let's say 1.7mm or even 1.8mm). This would not change much on your boost level, but may damp on possible shockwaves (just like a muffler) in your hose to the N75 and wastegate, so may eliminate your surging (im not 100% certain, so a test must be done). I still don't know whats the difference between C & F valve, since i haven't seen an F yet. Would be nice if you could check the stock restriction in your F one. The C has ~1.8mm, you cant insert a 2mm drill bit inside.
Looks like Mosser the guinea pig is gonna get to work again then!:D , i will take my N75 out after i've had some breakfast and make myself a restrictor and see what it does for me!,
Cheers Sim
Great!
Be sure to check the size of the restriction inside F N75 (try to determine as close as you can) and also be completely sure to use a bigger restriction than 1.5mm, i wouldn't like to read in your next post: i blew my turbo ;). In any case, try to log the results with VAGCOM and check your boost gauge regularly ;).
i have got a vernier so will be able to measure the hole size very accuratly and post the size, i will start with a 1.5mm hole as my turbo isnt capable of creating more than 24psi anyway (I've tested it with N75 bypassed!!)
Originally posted by Mosser
i will start with a 1.5mm hole as my turbo isnt capable of creating more than 24psi anyway (I've tested it with N75 bypassed!!)
:eek: :eek: You ain't kindding! Fasten your seatbelts then!!! :eek: :eek:
Do you already know where could you source a new turbo from? ;)
Certainly do!!, Mik from Impossible has an IHI turbo that should push me up to 280Bhp with a remap!, now all i need is an excuse to fit it ;o)
Ok, taken my N75 off now, here's the pictures, cant see any restrictors in any of the pipes at all as standard on the 'F' version, what do you think Sim?, do you need any different shots from different angles?
the restriction in my N75 is 1.65MM, do i need to add a restrictor to this same side of the N75?, or should it be in the inlet to the valve?
Originally posted by Mosser
the restriction in my N75 is 1.65MM, do i need to add a restrictor to this same side of the N75?, or should it be in the inlet to the valve?
So i suppose you have found the restriction by now then. It is best seen on pic3 however.
I have checked mine "C" version. I don't have any tool which i could use to do a correct measurement, so i put my 1.5mm drill bit inside, which fit it and the gap which left could be roughly 0.15mm, so the restriction on C & F valves should be the same.
You also should go for the 1.5mm i think. The restrictor should be put before the same line you have found the restriction in.
Here's a pic:
sportbilly
03-08-2002, 15:36
Just for the hell of it I have got hold of the required tools and equipment and made one of these this afternoon.
My car is not chipped it is standard so I am willing to give it a go to see what happens! :)
Drilled by hand which is not to difficult with a steady hand and decent drill and bits (I have a drill stand but no drill to fit it!)
I will see what happens ... back in a mo!
I am just connecting a 3 way bleed valve up with one port blanked off so that it works as an adjustable restrictor, i will fit it in about an hours time and se what it can do for me!
wish mosser would hurry up i hate waiting
:D :D
I've done it and tested it!!, i set it so that it had a significantly higher resistance to blowing through it compared to the N75 restriction (i would estimate it to be around 1.5mm restriction) and it hasent made any difference really!, still surges, but the ititial boost spike it biger than it used to be but sinks back quickly to what it used to be before,
I will play around with it tomorrow morning as i've got to visit the inlaws with wife in the car and she doesnt like me flooring it and then stopping to fiddle around under the bonnet!!
Hmm, then it must be the valve itself which surges :mad:. I got a C one and it doesn't surge for me luckily.
As for the higher initial boost; this is what exactly the restriction is meant to be. A lil' tuning for the low revs ;). The more the N75 will be restricted, the longer the initiall pull will be sustained.
When i had a 1.2mm restriction, the turbo boosted up till 4000 RPM like mad, BUT. And here comes a big BUT!!! Since it was way too restricted, the actual boost exceeded required boost a lot more than ECU would tolerate (like with 1.5mm for example), and ECU closed the N75 valve immediately causing a huge flat spot. Once ECU regained control over N75 again (at higher revs) everything was fine.
Originally posted by neg
I will see what happens ... back in a mo!
Neg,
broken down towing car or just having fun?! ;)
sportbilly
03-08-2002, 20:39
Sorry about the delay, had to take the missus out.
Ok Fitted and installed with no ptoblem at all, took it for a run and its seems to run fine. Not sure if I can tell the difference at the mo. Temp is quite warm and muggy so probably not best conditions ??? What sort of difference should it make ?? Would a smaller hole be worth trying.
The missus is using my car tomorrow so will have to wait until the afternoon to see if I notice a differnce ... then again I'm bound too I have to drive her car until then (not that there is anything wrong with her car ;) in case she reads this!)
I have left the old pipe in place at the mo so I can switch back in a matter os seconds if needed.
I can make another one or two if anyone wants to try it.
Cost me about £7 in total.
I have a picture for you to check which I willl post tomorrow as I'm off out now to get pissed as I dont have my car!
Originally posted by neg
What sort of difference should it make ?? Would a smaller hole be worth trying.
It should give you more low/mid torque up till 3500RPM. A smaller hole may cause you a flat spot after the bigger initial kick.
Come on guys! Tell me your experiences with this mod!!!
I've just taken the restriction out also put the original plastic DV in (instead of Forge) and my car feels pooooooo (hot weather tho).
i've fiddled around with the restrictor valve all the way down to no flow and none of the settings seem to give me more power or cure the surging i'm getting,
Others should get different results though because of the 1.3bar chip i'm running it isnt possible to push the turbo much harder than i do!
sportbilly
05-08-2002, 09:41
Drove the car to work this morning (14oC) and I must say it did seem to pull a little better.
It definately hasn't altered the car for the worse anyway.
I will run it for a couple of days like this and then out the straight through pipe back on to see if I notice the difference then.
I may also try one with a slightly smaller hole.
sportbilly
05-08-2002, 09:42
Sim,
which non-standard DV were you using ?
Originally posted by Mosser
Others should get different results though because of the 1.3bar chip i'm running it isnt possible to push the turbo much harder than i do!
Yes, im afraid your chip is already maxxing the turbo out. I'm actually surprised that you haven't got any problems with the turbo covering such a lot miles this way. The restriction definitely raised my boost on my 1.1 bar chip.
Neg;
I was (am) using a Forge DV006. Taken it off for re-greasing (maybe it will improve it) also considering to tighten the spring indise with a big washer.
My first attempt was a 1.2mm restriction, but i found it was too much for my chipped car. If you go too restricted, it will be almost the same like running your car N75 less which is dangerous. The 1.5mm instead of the 1.65mm restriction is a slight tuning only. Then as far as i remember you are running the stock chip. It will NOT inject more fuel when boost gets higher than 1 bar unlike tuning chips. It is dangerous to your engine as the mixture will be too lean resulting in severe temperature increase. BE SURE to monitor your boost somehow (VAG-COM, boost gauge, etc...) or just simply don't go more restricted than 1.5mm.
sportbilly
05-08-2002, 11:51
OK, I will leave as it is. I still will swap back to original in a couple of days to see the difference.
Just out of interest then on my standard setup what difference (if any) has this made (approx) - to boost /bhp ?
I have no idea. My chipped beezer got faster using the 1.5mm restrictor. Without the restrictor, the maximum torque (~300Nm, ~220 lbfts) felt later, so i suppose the turbo can spin up faster with restrictor on. It would be nice if somebody could do a VAG-COM test about power increase/delivery. I'll leave for holiday tomorrow, but will investigate the topic more further when got home. I'd like to see some charts ;)
sportbilly
07-08-2002, 10:26
After driving around with this mod for a couple of days (200m) I have noticed more power lower down the rev's 2500 - 3500, obviously as soon as you hit 4000 the power increases more through the VVT. I am going to remove this at the weekend just to see if I notice the difference without ... I will let you know.
Shock_Xe
11-08-2002, 19:59
I think ima give it a go but gotta try and get the right tools. Any1 out there fancy making them then selling them??
sportbilly
12-08-2002, 10:21
Sorry about the delay. I have been busy all weekend as I am looking at selling my house, had to go to a christening and then to top it off I am ill!
Anyway, I will remove the mod tonight and see If I notice the difference. Let you know tomorrow.
sportbilly
13-08-2002, 10:02
OK, I have removed the mod and drove the car a bit last night and this morning to work. To start with I wasn't to sure if there was a difference but after driving a little it seems that the boost below 3500rpm is not as good as it was. As the engine hits 4k its seems to respond like it normally does. Its not a massive difference but I can definately say the mod did not make it worse.
I will run it like this for today and maybe tomorrow and then put the mod back in place then to see if I can feel the change once again...
Could really do with some acurate figures from someone with a boost guage or RR.
sportbilly
13-08-2002, 10:47
Picture 1 ....
sportbilly
13-08-2002, 10:47
Another ...
Yeah, its not a massive tuning, just some slight mod. Funny as Mosser did not notice big changes on his Leon either, i think i may have a more significant boost increase on my Ibiza (fitted with C valve).
sportbilly
13-08-2002, 12:23
I'm sure when I looked mine is the C valve too.
Would be nice if somebody with VAG COM could try it and log the results.
Shock_Xe
13-08-2002, 14:51
I still cant werk out how where it goes (which pipe??) I got Vag com registered just gotta get a cable & £70 to pay for it
I'll try it as soon as I get my car back (with VAG-COM)
When that will finally be is anyones guess...
It wont be such a big mod you did last time to your car, ehh? :devil:
Shock_Xe
03-11-2002, 12:05
Originally posted by neg
I can make another one or two if anyone wants to try it.
Cost me about £7 in total.
Would you still be interested making another 1???
Any1 else tried this or contiuing to use??
thanks
Cuprasport2000
16-11-2002, 23:53
anyone else tried this?
:confused:
Shock_Xe
17-11-2002, 09:15
i just had one made but havent had a chance to give it a go, so ill let u know on this thread
sportbilly
18-11-2002, 14:14
I took mine off a while ago now as I had a funny dump valve type noise coming from the turbo .. or so I though. Turns out to be the K&N replacment filter I have installed. Suddenly started making this noise. Garage has checked everything and even fitted a new diverter valve to make sure, boost and all else is fine so I may put it back on to see if I can tell the difference.
Hi,
I tried that on my Leon and the results were crasy.
Before doing that mod, my car had 184 HP on wheels. Then we close the line to N75 completely, so no air come to valve and tried again.
The dyno showed 204 HP on wheels. That is 20 wheels HP.
But you all now, that you cant close that line completely, because you would destroy the engine, because of to less fuel.
So if you do that in the way you do that ( with restrictor) you could expect about a half of that HP.
So, that mod is realy good.
DEJAN
Had mine restriced for a while now, took it off the other day to see how it felt, Felt slower so this is a good mod!
I'll get around to trying this soon :p
Shock_Xe
19-06-2003, 13:02
i had one made up but taken it off when i had revo, didnt really notice any difference might try it again to see
It doesn't do any miracle, just gives a bigger spike. If your car's already close to the "limp limit", this mod may actually generate flat spots, so this might not work for everybody (just like different types of N75 valves).
karancsi
25-08-2011, 22:00
hi Sim,
i would like to do this mod on my 1998 passat 1.8t aeb, and i didnt find the pictures of the mod.
maybe if you have some you can share with me, or tell me in hungarian it is much more easyer.ohh an other thing,i have an ecu chip what is 1 bar boost and 1 bar fuel pressure i think, what do u think can i use this mod whit the chipped ecu safely?
thanks again and i waiting for your replay.
if you want you can send a message to my email address
pecsisrac20eves at freemail dot hu
br,Steve
sorry to bring this thread back up as any one tried this and have pics how to??
Bondiblu
19-09-2011, 08:32
I've found one of the hardest things with remapping is decent boost control which in my limited experience is hard to attain. Doing this mod just throws all that out the window and totally puts the PID controller out of callibration and will contstantly be fighting to correct actual boost verses requested. In general, VAG engines have more than sufficient air in the lower rev range to burn injected fuel, so pushing this up I think is dangerous, thats why tuners generally only raise the boost higher up in the rev range. Although I can see the fascination with a cheap mod, just be careful because it's very costly to fix a blown turbo or engine as we all know.
This is just my humble opinion