N75 differences?

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Nov 14, 2005 | 10:41 PM

#21

Shep 1.8T

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The vent hole vents air back into the intake

have you looked at the n75? it has three tubes. One that comes from the "cold side", one that goes to the wastegate and one that vents air back into the intake. That little sylenoid actuates to allow air to go whene the ECU deems based on load etc.

Nov 14, 2005 | 10:49 PM

#22

Shep 1.8T

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timing and tuning are designed around a set pressure

how much headroom do the injectors have left at 14 psi at say 6K rpm what about 7K? what about another 3 psi more?. While you are right the ECU will richen the mixture based on 02 sensors reading, I just wonder how close you are to running out of room up top. It's argueable, but the initial onset is still a leaner condition. How much more pressure till that little thing turns into a heat pump is another issue. I'de like to see raw data here.

the F is the suppersession for the C, there's no argurment about that. I'm talking about running a J, or K or this other crap.

Nov 14, 2005 | 10:51 PM

#23

Shep 1.8T

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yes..

your post seems to indicate that that is the rule instead of the exception though.

Nov 15, 2005 | 06:38 AM

#24

jprice@CPS

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you CAN'T run out of room (injectors) up top with the K03

The K03 won't flow enough to hold 14 PSI at redline.. it tapers significantly even if you weld the wastegate shut.

Knock voltages may potentially increase, causing ECU to reduce timing.

Either way, it won't go lean with the stock hardware. How do I know? I've done it, and watched all these variables with ECUx.

Nov 15, 2005 | 06:41 AM

#25

jprice@CPS

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Actually it doesn't send air one way or the other....

The vent allows the pressure between the n75 and the wastegate actuator to escape back into the intake (i.e. wastegate was being held closed, then throttle released... pressure that was holding the WG closed needs to escape)

On the JoeP MBC, the bleed hole vents that extra pressure to atmosphere (no, no BOV sound, and it's so little air that it doesn't make a noticeable/loggable rich condition.

Nov 15, 2005 | 07:04 AM

#26

Shep 1.8T

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if it doesn't direct air, not even the slightest bit

how does the wastegate actuate? It has to allow air to overcome the wastegate tension which is less than boost pressure. Point and case my setup, which will hold 20 psi till the end. If it just allows a constant state of flow my wastegate would open at like 7~8 psi, why am I able to make 20 psi unless that thing restrcits airflow to the wastegate till the ECU tells it direct air tothe wastegate and allow it to open?

Nov 15, 2005 | 09:09 AM

#27

jprice@CPS

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I'm saying it's not limited to directing air only to the WG actuator or the bleed side...

It can not allow air through at all. I realized I read your post wrong and though you meant that it either diverts air one way or the other (like a flap).. Sorry.. just read it wrong :-)

Nov 15, 2005 | 11:10 AM

#28

TmS4

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the feb 2005 issue of european car has a great article

it show graphs of all the boost, duty cycle, waste gate signal and other stuff. Very informative article.

I have had a c valve stock, f valve which is c updated, f feels smoother, I have tried the h it holds about 3 psi more.

if you are going to upgrade switch to f it is the same boost a the stock one but feels better. Audi does not sell c valves any more if you order a c they send you an f. If audi thinks it better and your car will like it, it is probaly true.