Turbo Upgrade Audi 100 C4 2.5 TDI AAT: Possible?

Hello!

I was just wondering if anyone has ever done something like this before? Last night, while falling asleep out of boredom, I was thinking about what I could change on my car (something that would actually make sense), and then it occurred to me that everyone says the old 2.5 TDI is so sluggish in the lower RPM range (it's already better with a chip ), and I once read somewhere (I think it was in this forum) that someone discovered a VTG turbocharger on their AEL (the 140hp version)! That made me think that you could definitely install that in an AAT as well, or at least the one from the 150hp T4. I was thinking of using the EGR solenoid valve to control the VTG linkage (of course, the EGR wouldn't work anymore, but mine hasn't been working for a long time anyway), because there probably won't be a free output stage available in the ECU (the ECU software would obviously have to be completely reworked, but I think many tuners could probably manage that)! Are there any experiences with this, and at what RPM would it really start to provide more power?I would appreciate any response!

Best regards,

Andi.

P.S.: I've also thought about the costs, and I believe that the software customization will be the most expensive part (after all, you can find 'turbo' kits on eBay like they're going out of style!).

Hi Andi!

The question is how the boost pressure is being regulated in your AAT now...

If it only works conventionally with a maximum pressure regulation system using a pressure sensor, rod, and wastegate, I would simply install an external, adjustable boost control electronics and connect it to your 'remaining' control valve, just like the vacuum actuator of a VTG turbocharger... something like that is available in a good tuning accessory shop (usually for gasoline engines ).

Otherwise, I believe that your AAT has a mass airflow sensor (MAF) and that the injection system already takes into account the previous LD configuration based on air mass... with a bit of luck, nothing will hit any (speed-dependent?) quantity limits, and the whole thing could work even without changing the engine control unit.

The LD setup likely starts similarly to the PD setups, beginning around 1300-1500 RPM... although the turbocharger needs to deliver a larger volume (1900 to 2500 cc), it is also supplied with a correspondingly larger amount of exhaust gas.

Best regards from Vienna.
Michl.

P.S.: The maximum allowable LD (likely referring to a pressure or load value) should be calculated based on the charger characteristic curves. However, since the 150PS PD (likely referring to a specific engine or component) comes with 1.5 bar as standard, a pressure of 1.0 bar should be achievable due to the increased air volume, and I estimate the limit to be around 1.2 bar.

Hi!

Yes, I think you are right! I apparently already partially dreamt about it; I actually thought that, for example, the AFN controls the LD via the pneumatic valve and the VTG !
Okay, it's best to just forget about the AGR valve ! Do you think I should use the solenoid valve, which currently regulates the LD (load) via a pulsed voltage, to actuate the VTG (variable turbine geometry) adjustment (of course, supplying the pulsed valve with vacuum)? And if it were to reach a software limit (I think the LD map just needs to release more LD a little earlier), that wouldn't be a big problem; it would just need a little tweaking! Because of my initial misthinking, I initially thought that a map for the VTG adjustment would have to be implemented ! Now, the only remaining problem is to figure out which turbocharger would be most suitable (which also has the most similar connections).

Greetings from sunny Leibnitz (as of today).

Andi.

Hi!

Yes, I think you are right! I apparently already partially dreamt about it; I actually thought that, for example, the AFN controls the LD via the pneumatic valve and the VTG !
Okay, it's best to just forget about the AGR valve ! Do you think I should use the solenoid valve, which now controls the LD with a pulsed voltage, to actuate the VTG adjustment (of course, supplying the pulsed valve with vacuum)?

So, for example, the AFN definitely regulates the LD (just like the AGR valve) via a solenoid valve that is supplied with vacuum from a small electric vacuum pump...

It appears you have the reverse (gasoline) version, which uses a diverter valve to regulate the boost pressure and direct it to a pressure sensor, which then controls the wastegate.

I'm not sure if your diverter valve (designed for overpressure) can work well with negative pressure... By the way, the control of the variable turbine geometry (VTG) is more precise and time-critical than the entire system in a wastegate. (There's a fundamental control loop involved: the load increases, and eventually the wastegate opens, regardless of how much the diverter valve does. In a VTG, there's nothing like that; everything has to be controlled by the regulator...

And if there's a software-related limitation (I think the LD map just needs to release more LD a little earlier), that wouldn't be a big problem either; we could just make a few adjustments!

Yes, so if you can/want to 'fine-tune' the LD map, that's definitely not a disadvantage!

Now, the main problem to solve is which charger would be the most suitable (and which one has the most similar connections)?

Well, I don't have an overview of all the possible VTG turbochargers that are installed in the market (or in the TDi engines).

The boost pressure multiplied by the air mass reaches its limit of approximately 1.2 bar in a turbocharged 150 horsepower engine (4-cylinder). I have no idea what boost pressure you are currently running (+ any modifications like a chip, etc.).

Perhaps there's something suitable from the V6 TDI group... they also have 2500 ccm.

When it comes to the connections, you will probably have to improvise...

....the position of the connections is not critical, and the compressor and exhaust housings can be rotated 360 degrees. On the compressor side, it is easy to connect hoses, pipes, and hose clamps to achieve the desired configuration.
A real problem could be the exhaust side... it might be necessary to have a massive 'adapter flange' manufactured, for example, to change from 3 holes to 4 holes, etc.... also, the connections for the oil lines must fit...

Conclusion: Overall, there are many details and uncertainties that still need to be clarified, but fundamentally, I don't see any insurmountable problem...

Best regards from Vienna.

Michl.