[Honziss]

Last week I was checking with Hartge.de regarding the power upgrade, this is how they do it:

The Hartge Engine Conversion is significantly different to other, often cheaper systems. Our Hi-Tech system contains many "smart" technical features, and is the result of many months of design, testing and durability trials. The investment we have made during the development program has resulted in a full 3 year warranty on the hardware and software, plus an insurance backed engine and drive line warranty, covering any effect of the increased power output for a period of 12 months from installation date, but limited to 6,000 Euro.

HARTGE engine upgrade is TÜV approved and legal in CZ.

Technical features are as follows; The Hartge ECU is an external additional control unit. It is internally sealed and cannot be detected by BMW service procedure interrogations. It is also not possible that BMW software updates can disturb the performance of the Hartge ECU. Unlike engine management "chipping" and "flash" upgrades, it never gets overwritten during service enhancements by BMW.

The Hartge ECU is connected via a special wiring harness to the standard fuel injectors, throttle pedal, exhaust gas temperature transducer and power supplies. There is no connection to the turbocharger, and we do not generate any influence on the turbocharger boost pressure, which could increase the risk of damage to the engine.

Additional power is generated by increasing the fuel injector injection rate by a precisely calculated number of microseconds, this number depending on engine speed and throttle demand and other parameters. This additional fuelling makes use of the excess air delivered by the turbocharger, and consequently additional power is generated. The BMW ECU continues to monitor all other important engine parameters as standard.

One of the safety features of the Hartge system is that it does not generate additional power until the throttle demand is increased to more than 70%. Therefore the engine behaves as standard until the driver demands the maximum power. This ensures that the standard emissions controls remain intact for the standard emissions tests and drive cycle testing.

There is also overload protection, which prevents full power from being delivered for excessively long periods of time, for example when towing heavy loads, or driving for too long at V-max. The Hartge ECU also prevents overload of the transmission at lower than 1,500rpm, and overstressing
the engine at high power outputs above 4,000 rpm.

In extreme temperature conditions, the Hartge ECU also monitors the exhaust gas temperature, and if this exceeds the safe limit, the Hartge ECU reduces power accordingly back to standard BMW power.

All standard BMW engine protection and emissions systems remain in place and continue to function.

It's not cheap, but it seems to be pretty safe way of engine upgrade...