N75J solenoid.

[amdeman]

Replaced the standard, 125,000km vintage valve with an N75J from the dealership (they didn't know what it was worth, got it for about the same price as the standard part).
Took 5 minutes, no 'idiot rashes', scratches, scrapes, all clipped into the position of the standard part.
Impressions; initially, didn't notice any difference. Second gear... OK, feeling slightly better. With moderate pressure of the accelerator 3rd gear felt like it was much improved. 4th even more so. 5th... Well, you get the pattern.
For the same amount of acceleration required noticeably less peddle. And kept pulling higher through the rev range.
Unsure what condition the original valve was in, and whether the differences are due to being better, or more serviceable; either way happy camper.

[h100vw]

Replaced the standard, 125,000km vintage valve with an N75J from the dealership (they didn't know what it was worth, got it for about the same price as the standard part).
Took 5 minutes, no 'idiot rashes', scratches, scrapes, all clipped into the position of the standard part.
Impressions; initially, didn't notice any difference. Second gear... OK, feeling slightly better. With moderate pressure of the accelerator 3rd gear felt like it was much improved. 4th even more so. 5th... Well, you get the pattern.
For the same amount of acceleration required noticeably less peddle. And kept pulling higher through the rev range.
Unsure what condition the original valve was in, and whether the differences are due to being better, or more serviceable; either way happy camper.

All they do is open and close directed by the ECU. Essentially they either work or not. I'd want to see comparison logs of boost and MAF before making a judgement as to whether there's an improvement.

It certainly won't be anything like a proper tune.

Gavin

[sambb]

I looked pretty deeply into the different valves a while back. There are slight resistance differences of the coils but I don't think that would result in any differences in performance. The main thing is that valves like the 'j' and 'h' have a smaller orifice in the bottom leg and/or different degrees of restriction in the leg that releases air to the inlet. Basically these have the effect that for a given amount of on time of the solenoid, less pressure will accumulate in the wastegate actuator thereby keeping the wastegate flapper shut longer giving faster ramp up or higher peak boost depending on how the orifices are configured. Some of the N75's (mine does) have a small adjustment screw in the top of the valve that can slightly alter the bleed rate through the long leg into the inlet manifold. I assume it is a factory set and forget but its almost impossible to adjust afterwards though.
Each valve was designed for different cars, engines and ECU boost curves and putting them on our car might be plug and play but its also a stab in the dark and whether that makes them work optimally with our fuel, timing etc is another thing. Like Gav said you'd really have to log it. There is definite value to modifying N75 air flows if you are suffering from overboost after say fitting a dump pipe though.

[amdeman]

All they do is open and close directed by the ECU. Essentially they either work or not. I'd want to see comparison logs of boost and MAF before making a judgement as to whether there's an improvement.

It certainly won't be anything like a proper tune.

Gavin

I agree; it is highly possible that the original unit was dead, or dying, and that this just fixed that.
As it turns out the car already has a tune, a REVO in it from Japan (score), unsure of what the tune is, or what parameters are set.
As yet, I don't have logging ability; it is on the wish list. By using SOTP-o-meter the car certainly pulls noticeably better, holds about another 500 / 1,000 revs before falling off the boil, using my local daily route, and 'markers' for comparison and reference.

[amdeman]

I looked pretty deeply into the different valves a while back. There are slight resistance differences of the coils but I don't think that would result in any differences in performance. The main thing is that valves like the 'j' and 'h' have a smaller orifice in the bottom leg and/or different degrees of restriction in the leg that releases air to the inlet. Basically these have the effect that for a given amount of on time of the solenoid, less pressure will accumulate in the wastegate actuator thereby keeping the wastegate flapper shut longer giving faster ramp up or higher peak boost depending on how the orifices are configured. Some of the N75's (mine does) have a small adjustment screw in the top of the valve that can slightly alter the bleed rate through the long leg into the inlet manifold. I assume it is a factory set and forget but its almost impossible to adjust afterwards though.
Each valve was designed for different cars, engines and ECU boost curves and putting them on our car might be plug and play but its also a stab in the dark and whether that makes them work optimally with our fuel, timing etc is another thing. Like Gav said you'd really have to log it. There is definite value to modifying N75 air flows if you are suffering from overboost after say fitting a dump pipe though.

Also agree. It's probable that I've just replaced an out of spec part with one that works back in serviceable working range.

Whatever the reason, car feels way more alive, more pleasing to drive, and has the mod bug playing with my mind.

[sambb]

is your car stock tune still is it?

[amdeman]

is your car stock tune still is it?

Trying to decipher your message. If I'm correct with it, the potential answer is that the isn't running a stock tune, unsure of the level of change.

[seangti]

I agree; it is highly possible that the original unit was dead, or dying, and that this just fixed that.
As it turns out the car already has a tune, a REVO in it from Japan (score), unsure of what the tune is, or what parameters are set.
As yet, I don't have logging ability; it is on the wish list. By using SOTP-o-meter the car certainly pulls noticeably better, holds about another 500 / 1,000 revs before falling off the boil, using my local daily route, and 'markers' for comparison and reference.

When they're dead, you know it. It will run on about 8psi boost, and that's slow... As mine died, it was intermittent, sometimes I had full boost, other times there was nothing. It may not be quite so obvious on a non-tuned car though, I can't really remember how they drive. 8psi boost on a tuned car makes you feel like you're driving a Nissan Micra, high throttle input everywhere. I had to replace my N75 on my 08 gti, just got whatever VW gave me according to VIN specs. It would have also throw an engine code if the old one was failing, if you can find someone who can scan it (even the free version of VCDS will identify it) and can clear it. It won't show the check engine light.

[amdeman]

When they're dead, you know it. It will run on about 8psi boost, and that's slow... As mine died, it was intermittent, sometimes I had full boost, other times there was nothing. It may not be quite so obvious on a non-tuned car though, I can't really remember how they drive. 8psi boost on a tuned car makes you feel like you're driving a Nissan Micra, high throttle input everywhere. I had to replace my N75 on my 08 gti, just got whatever VW gave me according to VIN specs. It would have also throw an engine code if the old one was failing, if you can find someone who can scan it (even the free version of VCDS will identify it) and can clear it. It won't show the check engine light.

In hindsight, always 20/20, the car has been on and off with performance.
Now it has a real 'urgency' with the way it responds and drives, compared to the lacklustre drive that it was.
I'm going to see a guy that does the REVO tuning / chipping here in Auckland and see what tune I've actually got, and see if there is anything to alter / improve.
Other than the valve; what else is there to change, that will allow more fun?
Looking at the I/C to T/B, and TIP, downpipe, followed by a tune for power, then suspension and brakes for the necessary safety aspect; what are the usual do's and don'ts with these cars?

[sambb]

Personally I'd do 3' downpipe +cat if money tight or full system if you have $, a retune to suit, then intercooler and then you'll probably want to spend money on not sliding off the road (dampers, bars, springs). You can waste a lot of money on plugs, DV's, silicon pipes, overrated CAI's - its all diminishing returns type expenditure really. Do the big stuff first.

[seangti]

Other than the valve; what else is there to change, that will allow more fun?
Looking at the I/C to T/B, and TIP, downpipe, followed by a tune for power, then suspension and brakes for the necessary safety aspect; what are the usual do's and don'ts with these cars?

How deep are your pockets? I started with suspension before any power.

For a tuned car I'd follow the path of the air. So air intake, either a DIY style, check out H100vw's (Gavin) build thread, pod form or a PD160 which is off a diesel Seat Cupra from recollection. It looks factory, but is larger than stock.

People have argued whether a turbo intake pipe (TIP) is the next best thing for bang for your buck, each to their own. I support the mod.

Consider your diverter valve, if it's stock you'd likely want to replace to ensure boost is kept under control.

FMIC - SeatSport are popular, Forge are ok. There are some very similar to SeatSport, just with thicker cores. Use the forge fitting kit or source parts elsewhere.

Then downpipe. A downpipe will require a new tune as it'll otherwise throw codes. Cat back won't gain bulk power, but a nice to have, DP will gain better results.

At this point you're be at around 140kwat. A perfect balance of power, reliability and drive-ability.

From here, bigger turbo, injectors, fuel pump, FPR, more tuning, etc, etc.

[seangti]

Personally I'd do 3' downpipe +cat if money tight or full system if you have $, a retune to suit, then intercooler and then you'll probably want to spend money on not sliding off the road (dampers, bars, springs). You can waste a lot of money on plugs, DV's, silicon pipes, overrated CAI's - its all diminishing returns type expenditure really. Do the big stuff first.

haha, between Sam and I, we've just nailed the two trains of thought at different ends. Sam's approach will give biggest bang for buck, though as I track my cars regularly, I'm more comfortable with the air-in, air-out approach given the driving conditions. For street driving, each to their own. I like to have the supporting mods in place to optimize the bigger ticket mods. I wouldn't say one is more right/wrong than the other though.

[amdeman]

Personally I'd do 3' downpipe +cat if money tight or full system if you have $, a retune to suit, then intercooler and then you'll probably want to spend money on not sliding off the road (dampers, bars, springs). You can waste a lot of money on plugs, DV's, silicon pipes, overrated CAI's - its all diminishing returns type expenditure really. Do the big stuff first.

Thanks for your input.
A 3" downpipe? That sounds large with such a small turbo?
I've already done a 2.5" mandrel bent exhaust (resonator and muffler was left over from the previous car).

[h100vw]

Thanks for your input.
A 3" downpipe? That sounds large with such a small turbo?
I've already done a 2.5" mandrel bent exhaust (resonator and muffler was left over from the previous car).

You might think that but it's not a downside. If you decide to go for a turbo change later, no need to redo the downpipe.

Gavin

[sambb]

Yeah 3'' dump isn't too big even for a K03. I agonised over whether to go 2.5'' or 3'' after reading stories about losing bottom end with the bigger pipe etc. I can honestly say I cannot fathom how anyone could say the 3 '' sacrifices bottom end. Mine spools so fast from so low, its too responsive down low if anything. Only prob with 3'' is that you cant just buy off the shelf dumps - it'd need to be a custom job. But 3'' feeding into your 2.5in system post cat would be awesome.