N75 valve - how does it work

[ChipHazzard]

N75s only cost a few 'squid'

tweak it haha

cheeky urchin

[S4TAN]

cheeky urchin

groan-mongous mate!

[viperbl]

OK, the one I had in before was a ... 078906283B

Remember that was probably the stock N75 on the RS4 engine ....

[S4TAN]

Remember that was probably the stock N75 on the RS4 engine ....

Yep - i think that's the case.

Does your new Q valve look any different to the stock B - or is it identical?

[yorkie]

My Cod I've won 10 Squid!

Could put that towards having my Mullet trimmed, or a new Barbel for my weightlifting set or just pay of some of the balance on my Goldfish card.

Or could just take the old Trout out for a drink.

Now I'm Floundering..

[viperbl]

Does your new Q valve look any different to the stock B - or is it identical?

It is different, its like all back to front if that makes sense!

I will try to get a picture, but I lack a digital camera at the moment!

OH DAM!! I seem to have lost 0.1bar of boost while talking about this!! here we go again on the lost boost journey!

[S4TAN]

will try to get a picture

MUST ... HAVE ... PICS!!!

[newsh]

Can I have a go please?
Primary boost control is via the spring in the wastegate, pressure in the inlet manifold is fed to the WG, pushes against a diaphragm, compresses the spring which opens the valve, diverting ( or "wasting") the exhaust gasses away from the turbine. Without a wastegate the turbo would just give more and more boost untill it self destructs (more boost = more exhaust gases=more boost.. etc.). The Waste Gate Frequency Valve (N75) sits in this pressure line and diverts some of the pressure that would normally open the wastegate back to the face of the turbo thereby allowing more boost than the WG spring would normally allow. This is the secondary boost control done by the ECU.

Duty cycle is a strange thing, you'd think you would just adjust the size of the hole in the valve to modulate boost but they don't do it like this. (cos you would need a proportional valve which is continually adjustable, the N75 is a simple open or closed type valve) Instead they modulate the valve, opening and closing it rapidly. The duty cycle is the ratio between the open time and the closed time and this controls how much pressure is diverted away from the wastegate.

I'm not that keen on fishing these days, although I was once sacked from a band for going fishing instead of to rehearsals..

[dodgydave]

if you don't clamp your MAP

How do you clamp the MAP? I've seen the H version and know the connector socket is rotated but i reckon i've got enough slack in the lead to still plug in ...

The MAP sensor measures up to 1.55 Bar, which is 5 Volt. You solder a Zener diode (4.7 volt) over the signal lines. This means the MAP will never measure more than around 1.3 Bar no matter what the boost is. You need a remap that requests more than 1.3 Bar tho!! Then you put a MBC in parallel to your N75, which enables you to adjust and run as much boost as you turbos can produce. The ECU works via airflow anyhow and will inject more fuel accordingly.

That's how a lot of yanks hombrew tune their cars.

But the best way is to get a decent remap !!! IMHO

[dodgydave]

http://forums.audiworld.com/s4/msgs/1584287.phtml

[viperbl]

So, with my new map, and on the basis that the MAP sensors can only read 1.55 bar, my max boost is worked out by the best the turbo can do ... ie, they are running at their physical max with the current actuators ?

[S4TAN]

Viper - I've just bought (and fitted) an N75 valve for the S2 (ABY) - it has a PN of 034906283K ... I reckon your Q34906283H was actually 034906283H (a "zero" not a "Q") ... the connector on the K version is rotated through 180deg .... had to do a bit of jiggery-pokery to get it fitted, but got it done.

Sourced it from vag-parts - they still do the H version (and a J version) but I went for the K as an experiment ...

The car feels GREAT running on this valve; really "perky" and instant response (also getting around 2-3psi more boost) ... Doug had a look and just tutted and grinned (but it was him who told me about doing this in the first place)...

If i blow my turbos then you can all laugh and say "told you so knobhead!" ...

[Peakz]

Perhaps this'll spice things up a bit in here . . .

http://www.norfolkantiquesandart.co.uk/prawnography/

[S4TAN]

Paz - I think you may need to see a therapist ...

[viperbl]

Viper - I've just bought (and fitted) an N75 valve for the S2 (ABY) - it has a PN of 034906283K ... I reckon your Q34906283H was actually 034906283H (a "zero" not a "Q")

I knew I should have not left scool at 11 You're right, it is zero, not Q

The car feels GREAT running on this valve; really "perky" and instant response (also getting around 2-3psi more boost) ... Doug had a look and just tutted and grinned (but it was him who told me about doing this in the first place)...

If i blow my turbos then you can all laugh and say "told you so knobhead!" ...

You know what you need ?? I boost controller!!

I can set mine so it boosts to 1.6 bar for example, for most normal spirited driving, then if that FQ400 or quick bike makes and appearance, a little turn on the knob and hey presto, we have that extra boost on tap! Can't go wrong