View Full Version : N75 - Not sure about this?
I have been told that a "J" type N75 would be better on my Leon over the standard one. Looking on other VAG forums this seems the case also as Golf owners have seemed to upgrade this.
I am a bit confused as the part that is on my car at the moment is an "F" type. According to Vagparts.com, the F type (part no 058906283F) is for an Audi S3 and is £33.54. The J type is for an Audi S2 (part no 034906283J)and is £24.57.
Surely the S3 would be better? I'm not really that technical on this side of things so not 100% sure!
:cheers:
Tom Harley
02-02-2004, 17:41
I've just removed a N75J from my Ibiza. Trading it in you see, so wanted to try and sell all the wee parts I've bought seperately. Looking for £20 + Delivery. Its only been on the car 2 months and I still have the receipt.
Tom
You could fit a H or J valve to your Leon, they will give you higher boost for longer than the F, smoother boost curve too. Cheap mod and worth doing - give it a go.
I'm not technical so I could be wrong here, surely an S3 N75 is designed to hold boost more than an S2 one? Or am I just not getting it!!!???
Is J definateley the way to go and is the above part number correct?
Changing your N75 valve on DBW 1.8T's is NOT recommended. While it has a positive benefit for non-DBW Golfs & Leons, I've read several negative posts on VW Vortex & UK MkIVs to put me off.
Eh? I've run both the H and J on my DBW Leon with very good results - every single car reacts differently, the only way to find out is to try one.
Eh? I've run both the H and J on my DBW Leon with very good results - every single car reacts differently, the only way to find out is to try one.
Interesting you say that. I've been umming and arring about getting one myself, but have been put off by negative posts in the States. What valve did you prefer, the H & J? My preference based on my research would be the smoother J-valve.
:cheers:
i've got the J in my leon, been in for over 10000 miles now. definately smooths out the acceleration, and haven't had any adverse effects yet...
but there still doesn't seem to be any technical explanation as to why it makes a difference, it's just a solenoid valve controlled by the ECU that in turn operates the wastegate
i'm guessing it's an analogue device and maybe it triggers the wastegate later than the stock N75... due to different spring stiffness? pipe diameter?
max_torque
05-02-2004, 07:35
There's no difference electrically between the various valve types, they just have different diameter orrifices up and down stream of the control pintle valve. This gives the valve a different "pressure drop" for any particular comanded duty cycle input. They still all effectively go from 0% DC (no leak) to 100% DC (leak as much as possible) but the different valve types mean a different leakage rate at 100% DC. Hence when you fit a different valve to your car it will disturb the boost control system. However as the boost control is adaptive it will relearn it's control, and the change in valve will only have an effect during transient conditions, ie when you rapidly apply the throttle, rather than under steady state wide open accel for example, where the system should still hit and maintain it's target boost pressure.
It really depends upon how "average" your car really is, on an average car the boost control system will adapt in the middle of it's "window of authority" giving plenty of space on either side for absorbing system changes, but if you have a car that say has a particularly good compressor, or a slightly too strong wastegate valve spring you may find that fitting the changed N75 valve will result in the boost control running into control issues ( over / under boost etc) as it may have run out of headroom within it's control parameters.
Originally posted by Getgaff
Interesting you say that. I've been umming and arring about getting one myself, but have been put off by negative posts in the States. What valve did you prefer, the H & J? My preference based on my research would be the smoother J-valve.
:cheers:
The J works better on my car, the H produced a small amount of surge on part throttle, the J is very smooth and produced more boost than the H.
Icecavern
05-02-2004, 09:29
Tried various different h75s on my Leon made no difference at all...
Pete
Originally posted by RobDon
The J works better on my car, the H produced a small amount of surge on part throttle, the J is very smooth and produced more boost than the H.
Did you have an "F" type valve to start with then? Still not sure if changing ti J will cock things up or improve them????
Originally posted by max_torque
There's no difference electrically between the various valve types, they just have different diameter orrifices up and down stream of the control pintle valve. This gives the valve a different "pressure drop" for any particular comanded duty cycle input. They still all effectively go from 0% DC (no leak) to 100% DC (leak as much as possible) but the different valve types mean a different leakage rate at 100% DC. Hence when you fit a different valve to your car it will disturb the boost control system. However as the boost control is adaptive it will relearn it's control, and the change in valve will only have an effect during transient conditions, ie when you rapidly apply the throttle, rather than under steady state wide open accel for example, where the system should still hit and maintain it's target boost pressure.
It really depends upon how "average" your car really is, on an average car the boost control system will adapt in the middle of it's "window of authority" giving plenty of space on either side for absorbing system changes, but if you have a car that say has a particularly good compressor, or a slightly too strong wastegate valve spring you may find that fitting the changed N75 valve will result in the boost control running into control issues ( over / under boost etc) as it may have run out of headroom within it's control parameters.
thanks max_torque, you certainly know your stuff. is the wastegate adjustable on the leon?