1.8t - N75 changed F to C, different boost characteristics

[wjspencer]

Hi everyone

 

1.8t 4x4 mk1 estate (ARX engine)

 

Some unusualness which, with all the knowledge and experience on here, I’m slowly getting my head around - so thanks! 

 

My car is stock and goes like stink, I think it has been remapped by a previous owner (I tried getting it remapped at Revo, they said the ECU was locked, potentially due to an old style remap, so they couldn’t remap). 
 

intermittent issue - I’d go for a run and get pretty much zero boost. I’d turn the engine off and on again and then back to full boost. 

 

No fault codes present, but forum searching suggested n75 at fault.

 

The N75 valve on the car was an F. I read that F was superseded by C. So bought a C. 
 

C installed I feel like the car boosts different. It ‘seems’ less powerful, but the mpg seems to have gone up. The boost curve maaaybe ‘feels’ more smooth? But I preferred how the previous valve felt. 
 

Too soon to tell if the intermittent no boost issue has gone but so far so good. 
 

Is what I’m experiencing expected for the N75 change from F to C? 
 

Does anyone recommend an N75 variant for a (potentially) remapped 1.8t ARX (150 when stock).

 

thank you in advance

[wjspencer]

Ok I’ve been driving with the N75c all weekend. Still getting the same (worse) power delivery. And MPG hasnt improved as previously thought. 
 

Turns out the C was superseded by the F and now E. An N75E is on its way, so I’ll be interest to see how that performs. 
 

When I was running the F the car felt really punchy. Could it be that the old style map was written for the F valve? And that using a brand new but outdated C valve doesn’t match the map? 
 

Hopefully the E brings her back to expected performance. I find it strange that there would be differences between the C F and E.
 

I’ll check all hose clips while I’m at it

Edited 24 March by wjspencer

[wjspencer]

With about 500 miles on the C, the F is back in. With the F, the increase in performance over the C is significant. There is more power all the way through the rev range. 

 

I still find it strange that there is such a big difference between the F and the C. I guess there’s a chance my car had been mapped to the F and so that’s the one for my car. 
 

The C is widely available, the F is hard to come by. The E is the current iteration of the valve, so I’ll try that when it’s delivered. 
 

Hoping this thread helps anyone with a 1.8t (ARX, elegance 4x4) wanting to renew their N75.

 

 

[wjspencer]

Ok so I’ve bought a genuine N75E. That’s in and the car seems to be boosting nicely just like the F. 
 

Time will tell if it solves my intermittent boosting issue on startup. 
 

I also found an N75J so looking forward to fitting that and seeing how it performs - if no good I’ll sell it on

[wjspencer]

So with E installed for a week now, boosting is nice as per F, but I’m still getting the intermittent boosting issue - perhaps even more frequently. 
 

I’m starting to think it’s the map at fault, assuming the car is mapped (feels like it…)

[wjspencer]

Ok N75J just installed and taken for a run 🤩

🚗💨