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The Audi S3 8V is a fantastic car to have, specially with the possibility of it producing around 500bhp flywheel with just a turbo kit upgrade. This is the reason why CTS Turbo made the Boss 500 kit. It is a direct replacement of the stock IS38 turbocharger, with housings machined to accept a Garret GTX28 turbo instead. The GTX turbo making everything more efficient for boost levels reaching 2bar. It makes so much sense to replace your IS38 and specially if your stock turbo was one of the early IS38 models that would tear themselves apart very easily – for no obvious reason even as stock. No more turbine wheels shooting out of your exhaust on this turbo kit.

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Upgrade specifications

  • 95RON fuel + Water-methanol injection
  • CTS Turbo Boss500 kit for EA888 Gen3
  • Upgraded downpipe
  • Etuners Stage4 ECU remap for Boss500, including electronic wastegate (EWG) delete for use with a boost controller

All sounds too good to be true. Most of it is good and true: as far as the turbo is concerned it really is a magnificent turbo, with one big problem. The recommended wastegate setup from CTS does not work. If you notice closely, CTS does not provide the actuator itself and you have to use the stock one from your car. And adjust it to work properly and that will never happen. In our case it would not work properly or reliably enough for the ECU to complete the adaptation procedure.

Then, when we managed to make it adapt, the settings were too soft and it would not hold boost as it should. Several redesigns of the hotside have been issued by CTS since the kit was first released. So far, we have seen none that worked properly out of the box. If you are stuck too we wish you good luck and advise patience!

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Modifying the Boss500 kit

When things do not work as they should, we try and find ways to make them work properly. Is it not what tuners are supposed to do – Find solutions to problems and make things work that were never meant to be put together in the first place: Out goes the dreaded electronic wastegate actuator that is controlling the turbo.

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In goes an electronic boost controller and a traditional boost-operated external wastegate actuator. So that the driver can control the boost levels and use different settings for daily drives or racing.

The mechanical modification required is very simple: Drill a hole onto the turbo’s exhaust housing, weld an external wastegate actuator. Tricky part is what comes next – convincing the ECU to give up control of the turbo and accept our commands via the boost controller. Through a lot of work on the Simos software, we made it possible for the car to forget it ever had an EWG and start behaving itself with the external boost controller. That was the part that we spent most of the time on, so that the ECU can retain its safety measures and protect the engine from immense overboost and leaning out Air-fuel ratios. In either case it will shut throttle and restrict airflow to protect its well-being. You can see it work in the dynograph below, testing the car at different boost levels via the boost controller.

Spending some quality time on Dynocom 5000 linked AWD dyno logging and fine-tuning the car provided us with excellent results.

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Water-methanol injection provides cooling and anti-knock protection for operating the engine at high boost safely, since 95ron (aka 91 oct in the States) is not ideal for stock engine/big turbo projects.

Performance results

  • Maximum horsepower at the wheels in 4WD: 422 whp@ 6000RPM
  • Maximum torque at the wheels: 397.5 Lbft @ 5100RPM

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Big thanks to Etuners in Panama!


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