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Author Topic: K04 Conversion - Looking for opinions & posting my progress/info about the swap  (Read 18611 times)

Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #30 on: April 18, 2024, 08:04:43 pm »
Aight, went with the second option. Got a $420 used K04 off of a 2.0 TFSI BWJ that the owner upgraded to a GT35xx, built the engine and is now pushing well over 600hp according to his dyno logs. Turbocharge is by no means new but for a 225k km charger is in a pretty good shape with close to no play in the compressor wheel. In case it does break later on, it's a $300-$400 repair which is still only half of what a brand new oem charger would cost (I've looked at the local prices again, they are higher than I remember). Now all I need is good weather and I can get started on putting this car together as it's currently on stands in my garage.

Will be the first turbocharger I install but luckily I have people to rely on in case I need info on anything.


Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline OllieVRS

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #31 on: April 21, 2024, 01:59:29 pm »
Nice to see you got a K04 for a good price and reliable seller - do you have the other supporting mods yet? Looking forward to seeing this running.
'06 Skoda Octavia vRS TFSI

Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #32 on: April 21, 2024, 03:55:22 pm »
Nice to see you got a K04 for a good price and reliable seller - do you have the other supporting mods yet? Looking forward to seeing this running.

So far here's what I've got

- OEM used K04 Turbocharger
- DV Relocation kit (Aliexpress)
- Charge pipe with DV relocation port (Aliexpress)
- K04 Turbo muffler delete with silicone connector hose for EA113 engines (Aliexpress)
- Air intake with sports filter (Ta-Technix)
- Downpipe with 200 cell cat (Ta-Technix)
- Turbo mounting kit (bolts, studs, seals)

The injectors, fuel pressure valve, sensor, map sensor and fuel pump internals will come at a later date. For now, I'll put the car together and chip it for 300-310hp. Later when I fit the VIS motorsport fuel pump internals, OEM cleaned injectors and the rest, I'll chip it for somewhere around 340-350hp but cap the torque under 480nm.

The same guy who sold me the charger is selling the complete OEM turbo piping kit including DV relocation excluding S3 intercooler hoses and the intercooler, for $200. Currently I'm waiting for better weather and more free time before I get started but I'm considering picking up his parts as well.

I figured these parts are not under a lot of stress so I can go Aliexpress. At the end of the day, they are just some silicone hoses, stainless steel tubes and CNC machined housings. However, I do plan on getting a complete ECS tuning boost pie kit later on when I get an OEM S3 intercooler.











Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline OllieVRS

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #33 on: April 22, 2024, 04:50:49 pm »
All looks good - but you will have to be careful, from what I read online upgrading turbo without injectors can lead to running too lean which is dangerous for the engine. Make sure the tuner is aware you are on stock injectors and you are limited. Perhaps 300hp is too optimistic without the fuel related mods?

Also the video you posted is private so I can't check it out.
'06 Skoda Octavia vRS TFSI

Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #34 on: April 22, 2024, 07:23:15 pm »
It didn't upload correctly for some reason, fixed.

Tuners here claim they can get 300 to 315hp out of just a turbo upgrade on stock fueling parts. I've already told the guy that I'm not installing any of those parts just yet but we'll see what the actual gains are eventually.

EDIT: Checked again, you are right, I need injectors too. Will speak with my tuner again to see if he can limit it to under 300hp to be on the safe side till I get a hpfp, injectors and other supporting parts.


« Last Edit: April 23, 2024, 07:29:44 am by ZoliWorks »
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #35 on: May 03, 2024, 11:19:45 am »
Aight time for an update!

I've taken off the old K03 turbo and I'm getting ready to mount the K04. Here's a video of the play in both turbines. The K03 has a lot of play in every direction, the 04 only has some sideways play. The 2 mechanics I spoke to said this is normal for it's mileage and as long as there's no back and forth play or damage on the walls/blades, it's good. Worst case scenario I'll just take it off again and get it repaired.


Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline OllieVRS

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #36 on: May 03, 2024, 05:14:57 pm »
Aight time for an update!

I've taken off the old K03 turbo and I'm getting ready to mount the K04. Here's a video of the play in both turbines. The K03 has a lot of play in every direction, the 04 only has some sideways play. The 2 mechanics I spoke to said this is normal for it's mileage and as long as there's no back and forth play or damage on the walls/blades, it's good. Worst case scenario I'll just take it off again and get it repaired.

Good update, this is also a useful post for anyone who's doubting the health of their own turbos so they can compare to yours.
'06 Skoda Octavia vRS TFSI

Offline pudding

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #37 on: May 03, 2024, 10:12:44 pm »
All looks good - but you will have to be careful, from what I read online upgrading turbo without injectors can lead to running too lean which is dangerous for the engine. Make sure the tuner is aware you are on stock injectors and you are limited. Perhaps 300hp is too optimistic without the fuel related mods?

Also the video you posted is private so I can't check it out.

It's all good in the hood. Just pull the N75 plug and you'll be restricted to 8 psi of boost and then fit the K04 injectors at the mapping place before the remap.  Probably makes more sense to fit the K04 injectors at home though and save on labour costs, but either way, it's drivable on K03 or K04 squirters before the mapping.

The main issue is whether or not the mapper can work around the rail pressure sensor.  Some insist on using the K04 sensor, and some can rescale the K03 sensor.



2007 ED30 | 2009 TDI 140 | 2016 BMW 330D

Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #38 on: May 04, 2024, 05:55:49 pm »
It's all good in the hood. Just pull the N75 plug and you'll be restricted to 8 psi of boost and then fit the K04 injectors at the mapping place before the remap.  Probably makes more sense to fit the K04 injectors at home though and save on labour costs, but either way, it's drivable on K03 or K04 squirters before the mapping.

The main issue is whether or not the mapper can work around the rail pressure sensor.  Some insist on using the K04 sensor, and some can rescale the K03 sensor.

No plans on fitting the upgraded injectors, valves or fuel pump just yet. This time around I'm simply adjusting the map to accommodate for the K04. In the coming months I'll be fitting all necessary fueling parts to push the car up to above 300hp with my target being 340hp, keeping torque under control cause of BWA rods.
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #39 on: May 07, 2024, 07:21:10 pm »
Alright, everything is put together the car starts and runs fine. I'm taking it to my buddy to get it mapped tomorrow. I drove it a bit but didn't floor it. Safe to say it works, no codes, no nothing, not even a lambda sensor code. I'll be back with an update after the map and after I iron out a few more things the V-band which links the 2 parts of the downpipe together didn't clamp on as it should and I feel like there's an exhaust leak there.

When I started the car, after a minute or so it started smoking quite heavily from the turbo area. Turns out, it was just the oil and brake cleaner residue that was burning off due to the heat.
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #40 on: May 09, 2024, 10:40:32 pm »
Another update, the car has been remapped and pulls like crazy! It charges a bit slower than a K03 but when the power comes on, it really puts a smile on your face.

However, we put the wrong map on the car due to a communication error and the ECU is expecting up to 130 bar fuel pressure from it, which the stock system cant deliver. When it reaches 126 bars, it cuts out and drops to 107. Above 5k rpm in 4th gear, the car is basically dead. I got the correct map done and we're flashing it tomorrow.

And the other thing is, there's a leak somewhere. I can hear it whistle every time I come off throttle. If I'm driving say 60kph and clutch in, the rpm doesn't fall to idle, it falls to 400, then shoots up to 1.5k and down again. If I clutch in when coming to a stop and I was revved to 3k, it falls down completely and the engine dies. I'll get the whole system smoke tested tomorrow.
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline pudding

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #41 on: May 10, 2024, 05:25:17 pm »
Good stuff.

I prefer the slightly laggy feel of the K04 for a more old school feel, but the harder hit in the midrange.  The K03 always felt more diesel like to me.  Good fun and punchy out of turns, but ultimately runs out of puff higher up the rpm.  Actually, the K04 isn't laggy as such, it's just that it hits harder when it does. VW quoted 221lb/ft at 2200rpm for the Edition 30 if I remember, which is torquier than it feels. That's the same torque as an R32 at the same rpm  :smiley:

Sounds like MAF related issues regarding your cutting out on overrun.  Might also be worth switching to the newest throttle body as well as they old ones were known to stick.


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Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #42 on: May 10, 2024, 09:53:34 pm »
Yeah it's definitely more punchy, that's fur sure. It has power past 6k and pulls throughout the powerband (2nd and 3rd gear). I don't regret the swap one bit. It sounds way better but that might just be because it's pushing 1.6 bar pressure almost all the time.
The throttle body was cleaned and tested, moves nicely. The MAF doesn't show any signs of being worn out just yet.

Now, regarding the loss of power and the leak. There is no leak. The map the car had demanded way too much fuel pressure and my fueling system can't keep up. We've changed the map so the car no longer stalls when coming off throttle or clutching in. It also drives a bit better but it still cuts out all the time past 5k in 4th gear or above. The map is still demanding 130 bar pressure sometimes and the stock fueling system fails to make that. I've seen it drop all the way down to 67 bar even and the idle pressure is 50!!!
Now the reason the car was stalling or idling rough when coming off throttle is because the ECU is still demanding the same fuel pressure off-throttle. Why VW did this? I don't know. What I do know is that if the fueling system can keep up, the car idles fine and doesn't stall.

Since there are no issues to speak of really, I've decided to keep it like this rather than restrict power as I rarely ever need to rev past 5k. With my daily commute being mostly city driving, I'm fine for a while. If there were no fuel cuts, the car would make between 290 and 300hp according to the tuner. It's definitely putting down power now, no questions asked, just not past 5k.


Next step, sometimes in the coming months, because I've spent way too much this past months, is upgraded fuel pump internals and a stronger fuel rail pressure valve.

TLDR: Car loses power past 5k rpm not because of vacuum leak but because of fuel cuts.


Side note
I've been switching between the DV+ and the revision D valves. Both can hold pressure equally well but the DV+ makes it sound like a supra when coming off throttle because it can't let out pressure fast enough. My mechanic/tuner said this isnt all that bad for the turbo, but the ECU doesn't like it one bit. It's constantly throwing "pressure release valve mechanical failure" errors. The rev D is fine but sounds average, as expected. I've switched back to the D for now but if I want to show off the car, I'm putting the DV+ on. It's a 2 minute job anyway since the relocation kit brings the valve to the front of the engine, right next to the throttle body.
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp


Offline pudding

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #43 on: May 11, 2024, 12:48:04 pm »
Yeah I wouldn't go past 1.6 bar personally. The journal bearings don't like it and it's starting to surge out of its efficiency zone at that pressure ratio, but should be OK if you do regular oil changes and have a better intercooler. 

I found 1.5 bar to be the sweet spot for the power to lifespan compromise.  Stock S3s ran 1.2 bar for 265hp, so there's not a massive amount of headroom. Borg Warner quote a sustainable 300hp max for the K04 but they're capable of more in short bursts. Poor tuning can crack them around the wastegate as bad tuners they don't control the EGTs properly, or turn off component protection completely.  I've seen a complete fracture of the entire housing as a result of that.

Is your throttle body a VDO one? If so, I would swap it for the newer Continental one. I had surging and throttle valve flutter issues with the gen 1 VDO throttle after it was tuned.

How many grams/sec at idle are you seeing?  Normally around 2.5 - 3 g/s at hot idle.  When my MAFs used to go, it would dip below 2 at cut out.  Surging from the turbo used to fling PCV oil up into the turbo intake pipe and soak the MAF. It's a really poor location.  VW moved it much further away from the turbo on MK6s onwards for that reason.

VW just close the injectors on overrun and open them again around 1200rpm to give the idle control map time to kick in. The HPFP being mechanical will still be making pressure.

Need to be careful with the rail pressure drops as 25% lambda is the maximum compensation.  Below 80-90 bar it runs out of options, retards the ignition (which also has an adjustment limit) and then it detonates because it's too lean.

You definitely need pump internals, and maybe the RS4 pressure relief valve as well as the stock one cracks open at 128ish bar.

I never had any problems with a Revision D, but there are some silly myths about them being 'designed to leak', which is nonsense.  My DV+ failed. The rubber pad unglued itself and fell off.  Really poor design.

















2007 ED30 | 2009 TDI 140 | 2016 BMW 330D

Offline ZoliWorks

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Re: K04 Conversion - Do you ever regret it? How is it for daily driving?
« Reply #44 on: May 11, 2024, 09:43:19 pm »
Car is running 1.54-1.58 bar (actual) at WOT and the specified is 1.55 max. It's surging till 4.2k or so and then quiets down. For now it's a stock cooler but I'll be picking up an S3 cooler cause I can feel it losing power.

I'd have to check, not sure. It's surging all the way from 3k to 4.2 or so in 4th gear and above. In 5th, it's surging from even lower rpm.

2.58-2.72 g/s. The MAF is a tiny bit oily, like slight surface oil. Under WOT the highest I got was 240g/s

I'll deffo be fitting pump internals and the pressure valve.

Same here, no issues with the rev D. it holds boost fine and seals quite good even when not powered.


« Last Edit: May 11, 2024, 09:51:08 pm by ZoliWorks »
Mk5 Jetta 2.0 TFSI BWA | Mk6 GTI Front | BorgWarner K04 Turbo | Ta-Technix Air Intake | Ta-Technix 200 Cell Downpipe | Stock Intercooler | Stock Injectors | Vis Motorsport 175 bar HPFP | 300hp