Tuning N75 valve.

Sim

who?
May 24, 2001
1,700
0
Budapest, Hungary
www.ignitron.net
As we all know our N75 valves do limit the performance of our cars, many of you are thinking of purchasing aftermarket N75 valves. I had lots of time spent of buggering my N75 valves as it seems that a perfectly(!) working N75 valve was messing up my power delivery big time, finally my problem got sorted by replacing it to another one.

While examining and learning the operation of the N75 valve, i came to the conclusion that it is possible to do a slight modification on -- let's be more precise, before the N75 valve so it will practically behave as a "race N75" valve, causing the turbo to spool up more quickly and hold boost more firmer/further.

What is the N75 valve?

The N75 valve is connected between the turbo's wastegate and the turbo's high pressure output. When the turbo spools up, the boost it produces will open its own wastegate, preventing it from making any more boost (as a kind of protection). This threshold value is set somewhere at 0.3 bar, so when our turbos produce 0.3 bar it will be adequate to open its own wastegate and stop producing any more boost.

Here comes the N75 valve. When ECU wants more pressure than this 0.3 bar, it wents (bleeds) some boost from the turbos wastegate using the N75 valve, so the turbo will produce the required amounts of boost. When the N75 is bad (not wenting boost from the wastegate) or set up wrongly (wents just a few air), the boost level will be a lot lower than requested.

Here comes the trick.

Since the wastegate is air operated by the N75, we may slow down the operation (opening/closing) of the wastegate (which will result in faster boost build up and slower boost release) by just simply restricting the air going into the N75. Before you would ask; "should we do that?! won't it hurt the engine?!", the N75 ALREADY has got a restriction in it, we just gotta do some fine tuning. As you also can see on your own engines, the piping going to/from the N75 has got around 6-8mm inside diameter, BUT the actual diameter is not bigger than 2 mm where air can enter into the stock N75. Since you cant do anything inside the N75 (and also to keep it stock) a restrictor should be put anywhere into the piping between the N75 and high pressure part from the turbo (it's the metal pipe going to the IC on 20VTs, from where N75 gets the boost to operate the wastegate).

What is a restrictor?

Anything which wont let through air at larger diameter than lets say 1mm-1.5mm (stock restriction is ~2mm). A 3-4cm long aluminum rod (~6mm diameter) with a 1mm hole drilled thru its middle would do the trick.

I have not tried this myself yet, but theoretically it will work. Do not misunderstand, I am not encouraging anybody to try this, as an unskilled individual may actually damage his engine by introducing metal filing into the combustion chambers (from the restrictor), but it is a very low budget modification which would cause noticable increase in driveablilty and power. As a side effect, it also may eliminate surging.

What do you think about that?
 

Mosser

The King
how about using a 3 port bleed valve and blocking off one of the ports so that you can fine tune it to restrict the air flow?, should be really easy that way, might give it a go tomorrow,

I got an Email back from ECS today stating that their racing N75 isnt designed and is unlikely to stop my surging, they said it has worked for a few people but the only way i can find out is to buy ine and try it!!, so if the blocked port bleed valve doesnt work tomorrow(i've got one laying around somewhere) i will be buying a dawes device!
 

Sim

who?
May 24, 2001
1,700
0
Budapest, Hungary
www.ignitron.net
Dawes device should be a great way of increasing chipped 20VT power. Using my car with no N75 valve for some laps made me sure that there must be done something to the stock N75 as it is so crap...
 

smithrc

Sold - Oct 2006.
Bill, Did you ever fit the Dawes device?

Guys, re: The blocking off of n75 valve on standard 20VT

So I could get more power out of it as standard... yyes?
but the boost is running upto 1.3bar... yes?

If the 'valve' inline to it works, will this be an adjustable, cheap, mod for slight gains?

I understand the perils of running lean but wont the ecu adjust to suit?
 

Sim

who?
May 24, 2001
1,700
0
Budapest, Hungary
www.ignitron.net
Smithrc,

I would not suggest to block/unhook the N75 on a standard car. No sufficient fuel is mapped for the highly increased boost, which will cause that you will be running way too lean. For 1-2 laps it's OK, but in longer term you will damage your engine. It is said that the standard fuel mapping is safe up to 1 bar of boost, but anything above that and you'll be too lean (causing melted pistons in worst case). N75 unhooked the way i described (not completely taken out) in an earlier post causes up to 1.3 bar in spike and 1.0 bar almost till redline, which gives an AWESOME performance to the car ;). Chipped cars usually have fuel mapped up till 1.2-1.3 bar.

By putting just a simple dawesdevice on the engine (instead of the N75) taking care that the boost is NOT hitting the 1 bar (not even in spike), you should gain a nice and constant power increase over the stock setup for just a little bit money.
 

ibizacupra

Jack-RIP my little Friend
Jul 25, 2001
31,333
19
glos.uk
Originally posted by smithrc
Bill, Did you ever fit the Dawes device?

Guys, re: The blocking off of n75 valve on standard 20VT

So I could get more power out of it as standard... yyes?
but the boost is running upto 1.3bar... yes?

If the 'valve' inline to it works, will this be an adjustable, cheap, mod for slight gains?

I understand the perils of running lean but wont the ecu adjust to suit?

I still have it somewhere, not fitted it tho.
Not from Daweas Device, it was from one of my suppliers. Same thing tho. £30 as I remember.

regards
Bill
 

smithrc

Sold - Oct 2006.
Fair enough if i was just to blank it off - but will an adjustable valve allow the boost to be adjusted?? thererfor allowing just under 1 bar to be achieved?

Bill - If you felt like you wanted to pass it my way - I'll fit it and test it on mine for you.

If it works - I'll buy it too! ;)
 
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cupra monster

Guest
hi, just finished my n75 restrictor!!!! did not work with 1mm hole, this did not work. so i drilled up to 1.5mm and WOW the power is awsome. then i adjustered the waste gate 3 full turns to the right. now its holding boost all round the rev range. stuck HKS dump valve on and its like a remap:clap:any one got any more mods i can try?
 

cupra monster

Guest
this mod turns it in to a flying machine, with 180BHP insurance :funk:
 

GregM

Active Member
Jul 13, 2010
97
0
Chelmsford, Essex
Is this something I should defiantly look into doing? At the moment I'm concentrating on doing cosmetic bits and bobs (wipers, splitter, wheels and some colour coding)

It's unlikely I'll start doing anything to the engine for a couple of months and as such its completely standard under the bonnet, so am I better off waiting until I've got an induction kit / 007dv / n249 bypass before bothering to do this?
 

cupra monster

Guest
thats what i was doing, the only thing i have done is put the HKS on, and a good mushroom filter, about £250 pounds wouth, did the restrictor and the waste gate ajustered, its trying to spin in 3rd gear i can not belive you can get so much power from a 3 cm long ally rod with a hole in it.
 

cupra monster

Guest
get the HKS valve you will cream yourself when you hear it,,WWWOOOOOOSSSSHHHH
 

leon_cupra_666

Guest
Hi guys has anyone got any pics of this mod so i can see what the restrictor should look like and where it should be fitted?
 
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