Author Topic: n75 J valve a bit of a mith ?  (Read 28411 times)

Offline G0LF_GT1_TURB0

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n75 J valve a bit of a mith ?
« on: 19 September 2011, 10:27 »
just seen this, i know its a few years old, but it has got me thinking of keeping my standard valve instead ?? any recent proof that the J 'actually' works ?

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Offline Len

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Re: n75 J valve a bit of a mith ?
« Reply #1 on: 19 September 2011, 10:39 »
I think Dom69 has fitted one!
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Offline F17BAD

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Re: n75 J valve a bit of a mith ?
« Reply #2 on: 19 September 2011, 12:24 »
i might need a new N75, the J valved is a replacement, nick at carbon checked on Etka whilst i was their (we were looking at the one for my engine which is a F valve) it said replace with the J valve. thats the latest one..

so i assume if the one on your car is broke you just replace with the latest version which is J ?
  


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Offline tshirt2k

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Re: n75 J valve a bit of a mith ?
« Reply #3 on: 19 September 2011, 13:05 »
Usually the letters on the end mean it superceded to an updated version. 


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Offline RTechUK

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Re: n75 J valve a bit of a mith ?
« Reply #4 on: 19 September 2011, 13:43 »

The N75J K H valves cause the turbo to over boost to give the feeling of a BIGGER kick of power,  for everyone not running the OEM N75 stock or mapped can you do some logs and post your results up?

Plot of an AUM with N75C valve as you can see the boost plots are following the remap requested levels, which is correct to the mapping and is correct.


Same car same mapping BUT with the N75J fitted now over boosts to 2270Mb from the requested 2000mb... Just a quick cheat to make power, but the ecu will soon learn over time, so when you first fit the J the boost kicks hard, then over a period of time will end up where it should be. (until battery disconected or adaptions reset)


It would be cheaper and better to change the max load map from 157% to 174% in the mapping to take the requested boot to 2270mb instead of adding a and uncontrolled boost spike?

The H J K valves are designed for the K04 turbos the C F E are for the k03/s turbos.

Edit H J K designed for bigger slower spooling turbos such as the ko4, and C F E smaller quicker spooling turbos or car with high dc n75 maps)

Fitting a H J K valve to a k03  turbo and ecu will induce a turbo faster spool and more over boost in the mid range, but the ecu soon adapts and pulls the boost back in to line which can be seen on the N75 logs.  The H J K valves will reduce the power at the top end againback to back you can see the n75dc working harder to maintain boost.  Its the feeling of a kick which the H J K valves give the smaller turbo which makes ther driver feel like the car is faster, but at the end of the day the average power it about the same, in some cases lower.  The ecu is designed to meet load/boost once this load has been meet the ecu will cut the boost back via boost controller PIDS, which are there to stop boost over/under shoot oscillations (not an easy ecu to fool)

For all of you who want to understand boost pids here is a copy of a wiki page for me7 tuning. 

(Just to note the PID I is  what  I use to give the car the kick of boost or linear boost depending on the mapping and customers needs)


Boost PID
If your actual boost is not meeting requested boost, you may have to increase the PID I limit between 2250 and 5000 RPM for 850 and 1000mBar:

KFLDIMX - LDR I-Regulator limit
To go along with KFTARX above, there is another IAT correction that ME7.1 uses to allow the PID to add waste-gate duty cycle at elevated IATs. You may want to zero it all out:

LDIATA - LDR I-Regulator limit as a function of IAT
If you aren't using K03s, you may have to tweak the PID response. Note: this is NOT used to adjust requested boost. It is used to compensate for different waste-gate responses.

KFLDRL - Map for linearization of boost pressure = f(TV). This is the post-PID waste-gate duty correction table.
LDRQ0S - LDR PID Q0 in static operation (proportional term)
LDRQ1ST - LDR PID Q1 in static operation (integral term)
KFLDRQ2 - LDR PID Q2 (differential term)
KFLDRL can also be used to get open-loop type behavior for operation past the MAP and requested boost limit by making the output duty cycle unresponsive (flat) to uncorrected duty cycle (from the PID) at various RPM/DC points. Again, if you do this, make sure to leave DSLOFS at the stock value! This way, requested boost will always be higher than measured boost, and you will stay in open loop control.

With after market or external waste-gates flat line the map at something like 25% until your turbo should be spooled and then taper off to 10% at areas if higher load and RPM. Log requested vs. actual boost to see where you need to adjust KFLDRL to line things up. The higher your after market waste-gate spring pre-load the lower the WGDC you will need to accurately control boost.

If you don't get all of this just right, and your actual boost goes too far above requested boost (by ~200mBar), you may experience overboost throttle cut, which is ME attempting to get boost back under control by temporarily closing the throttle plate.

Alternately, if your requested boost is far too high for a given load/rpm point, you may experience positive deviation (underboost) limp mode.


Many hours go into getting the boost pids correct.

IMO £90 for a valve to give that feeling is a waste of money, as its only a 5 min job to change the boost PIDs in the mapping to give the same effect and actually make more average power with out tailing off at the top end.


« Last Edit: 20 September 2011, 08:55 by RTechUK »



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Offline dom

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Re: n75 J valve a bit of a mith ?
« Reply #5 on: 19 September 2011, 17:38 »
I think Dom69 has fitted one!

I do indeed, I also have a dyno plot of a standard N75 fitted. Following the RR day I will also have an after plot, I'm expecting the N75J to smooth the graph out, especially at around 3500 rpm :smiley:

Offline dom

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Re: n75 J valve a bit of a mith ?
« Reply #6 on: 19 September 2011, 17:41 »
Just to further this, here is my car running the standard N75:



Here is another forum member's car with exactly the same map but running an N75J valve:



Note how my flat spot at 3500rpm isn't present on the second graph :smiley:

Offline RTechUK

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Re: n75 J valve a bit of a mith ?
« Reply #7 on: 19 September 2011, 18:04 »
Smoother in the mid range but dips off at 4900rpm, but was the runs vs the old N75F and a new J?


Will you be trying a run with a brand new N75F aswell?  It would be nice to see runs back to back with all valves



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Offline RTechUK

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Re: n75 J valve a bit of a mith ?
« Reply #8 on: 19 September 2011, 18:12 »
I will try and get a AUM to borrow and load it with a Revo trial map and test all the valves (brand new) back to back with dyno logs.

Here are Wellys tests with the valves on an K04-023.

http://www.audi-sport.net/vb/a3-s3-forum-8l-chassis/101557-n75j-n75c-mbc-comparison-graphs.html



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Offline dom

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Re: n75 J valve a bit of a mith ?
« Reply #9 on: 19 September 2011, 18:13 »
Smoother in the mid range but dips off at 4900rpm, but was the runs vs the old N75F and a new J?


Will you be trying a run with a brand new N75F aswell?  It would be nice to see runs back to back with all valves

Yeah it's an old 'F' vs new 'J', If anyone there on the day has a new 'F' then we can swap them over & do back to back runs, however unless that's the case then we'll have to settle for old 'F' vs new 'J', I'll have both with me on the day so we can do back to back runs if need be.