N75 valve upgrade

gezmeister

I need a derv!!
Apr 1, 2008
2,172
0
Norwich
Just wondering how many of you have upgraded the n75 valve to an n75J? Is it worth doing to a standard car, or more worth doing after a remap?
 

andycupra

status subject to change
from what i have read here some time ago when people were experimenting with this, going to a J was a bit hit and miss from car to car.

IMO if you are going to get remapped, then stick with the standard N75 as the map will be based in the N75 being stock. You could cause overboost issues with remap and J.
 
Aug 2, 2009
812
0
North Lincs
Calm down mate, i was hardley being a keyboard warrior!!

I spent about an hour looking through threads about the N75 yesterday and came to the same conclusion that andy has posted above.
 

turbin

Guest
ho ho ho, merry xmas everyone =D


I use the N75"H" version on my remapped LCR. And I get pretty much 1-2 psi more boost across the rev range. + a MUCH faster pickup.
 

gezmeister

I need a derv!!
Apr 1, 2008
2,172
0
Norwich
Calm down mate, i was hardley being a keyboard warrior!!

I spent about an hour looking through threads about the N75 yesterday and came to the same conclusion that andy has posted above.

It's just how you came across. I'm hardly a newbie, when i want to know something, i use the search where possible, and only post a question if the search doesn't answer it. So back to the original question, and just to add a twist to it:

What would be the difference between a mapped lc with a normal n75, and an lc with an n75j?
 

cuprastupot

Eleanor
Aug 27, 2009
60
0
Chester & Crewe
Iknow it can be hit or miss with this valve i just put a n75j on my stage1 mapped cupra and it wont boost over 12psi in any gear. Does it need time to adjust or should it be instant.

Been as it wont boost any more than 12 does this mean its in limp mode - i have no fault codes come up on the liquid gauge.

The stock n75 was boosting at 18.5psi then dropping to around 14psi.

Wondered if this j valve is best fitted before i got it mapped or used at stage 2 instead.
 
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andycupra

status subject to change
it should be instant.

As ive said before, if you put this on a mapped car you may find yourself tipping it over the limit and the ecu pulling boost back.

You say should you have put it on before it got remapped, or at stage 2..
well both revo stage 1 and 2 will have been developed assuming it had the stock N75 on the car..
also revo is a generic remap (althugh clearly has ability to be adjusted somewhat with the sps device) and so fitting the N75 before the remap would not have changed what map was uploaded.

Stage 2 would be the same, although it is possible stage 2 may not be affected in the same way as i believe the boost does not come in so aggressively.


If you got a true custom remap, then yes you shoud put all mods on before the remap, but then a true custom map would be more money and time, and in any case, if you put a Jvalve on it doesnt mean it will end up running any more boost than a stock valve as the mapper would simply map according to the hardware you have

What is the reason you put the J valve on? - just to get more boost? - if so you can up the boost with an sps controller.

And remember, more boost or higher timing doesnt always mean more power. There are limits and running to high boost or timing that isnt suitable will actually mean less power.
 
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andycupra

status subject to change
and just to add a twist to it:

What would be the difference between a mapped lc with a normal n75, and an lc with an n75j?

the mapped LC with a normal N75 would be much faster than a stock car with a JN75.

A remapped cupra with stock N75 woukld be noticably quicker.
If you put a J valve on a stock LC most people would find it very difficult to notice the difference.

Or in short there is no comparison. (J valve may add 1-2 psi.. a remap may add 10)
 

cuprastupot

Eleanor
Aug 27, 2009
60
0
Chester & Crewe
it should be instant.

...What is the reason you put the J valve on? - just to get more boost? - if so you can up the boost with an sps controller.

And remember, more boost or higher timing doesnt always mean more power. There are limits and running to high boost or timing that isnt suitable will actually mean less power.

Yes it does feel it has been tipped over the limit so i have put the stock valve back on and now boosting back to normal.

I decided to change the valve because i read and was under the impression that it would hold out to higher boost levels as mine was dropping to much boost further up the rev range.

Not clued up on that sps controller and if its worth investing in - is that from revo? will do a search.

Cheers for the info.
 

andycupra

status subject to change
sps controller from revo allows you to adjust the boost levels and timings.

however you will not get to stop the drop off in boost at high revs, as this is simply due to the fact that the turbo cannot hold that amount of boost high up the rev range.
(if you imagine that at 3,000 revs the quantity of air being boosted will be half that at 6,000 revs..)

you could reduce the boost levels which would in turn reduce the drop off... but then you are running lower boost so no doubt will moan its down on power.
At the end of the day running high boost means at the top of the rev range its out of its possible performance limits so you will get a drop off when remapped.
 

turbin

Guest
sps controller from revo allows you to adjust the boost levels and timings.

however you will not get to stop the drop off in boost at high revs, as this is simply due to the fact that the turbo cannot hold that amount of boost high up the rev range.
(if you imagine that at 3,000 revs the quantity of air being boosted will be half that at 6,000 revs..)

you could reduce the boost levels which would in turn reduce the drop off... but then you are running lower boost so no doubt will moan its down on power.
At the end of the day running high boost means at the top of the rev range its out of its possible performance limits so you will get a drop off when remapped.

thats interesting.. bcs with the oem N75 valve Id always see 13psi at redline where now with the "H" version Im at 14-15psi at redline... 3rd gear.
 

greesha

Leon 1.8T on steroids
Jan 6, 2009
496
0
Slough
I have N75J on mine and car seems to hold boost longer. Unfortunately no boost gauge fitted yet
 

andycupra

status subject to change
thats interesting.. bcs with the oem N75 valve Id always see 13psi at redline where now with the "H" version Im at 14-15psi at redline... 3rd gear.

im not arguing that the J valve shoud give you higher boost. Its basically delaying the signals it sends to the ecu so im not surprised the J valve sees slightly higher boost.
But presumable you are still getting a drop off from the peak value so it hasnt got rid of the drop off. Although potentially it may be slightly higher up the rev before the drop off.
Higher boost is not always good though
 

turbin

Guest
im not arguing that the J valve shoud give you higher boost. Its basically delaying the signals it sends to the ecu so im not surprised the J valve sees slightly higher boost.
But presumable you are still getting a drop off from the peak value so it hasnt got rid of the drop off. Although potentially it may be slightly higher up the rev before the drop off.
Higher boost is not always good though

True with the higher boost at hight RPM can be bad.. but 15psi instead of 13psi... should be well within tolerances.
 
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