Cheap N75 mod for everybody

[Sim]

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;

 

[Sim]

another one

 

[Alf]

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

 

[Sim]

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]

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

 

[smithrc]

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

 

[smithrc]

thats better

 

[Shock_Xe]

So what did you do?? just put 2 jubilee clips on????

 

[Sim]

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" . 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:

 

[Sim]

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]

Something for the weekend ....


If anyone gets this done easily then you may want to think about making a few extra ... catch my drift !!!

 

[lozza]

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.

 

[Sim]

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.

 

[Mosser]

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 ?

 

[John]

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]

Actually my uncle has a laith as he has just started up a business!!!!!

 

[Sim]

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.

 

[Mosser]

Looks like Mosser the guinea pig is gonna get to work again then! , 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

 

[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 .

 

[Mosser]

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!!)