Electronics – AUDI QUATTRO RALLY CAR MANUAL

Electronics

Arguably the single greatest step in motoring through the 1980s was the adoption of electronic engine management. By giving the engine a ‘brain’ (otherwise known as an Electronic Control Unit or ECU), it became more efficient, while men with laptop computers could write programs to deliver the optimum balance of fuel efficiency and power output.

Early ECUs would measure the load and speed of the engine and adjust, with the data being read by a microprocessor to then manage the fuel flow appropriately. As the capacity of the computers grew, so they were also able to process information on ambient temperature, rpm, throttle position, air pressure, and oil and water temperature to make instant adjustments via solenoid.

From 1980-83 the Audi Quattro rally cars used a combination of Pierburg’s fuel injection system and a Hitachi ECU. As the Group B era began to demand more power, higher turbo boost and the need to fine-tune the point of ignition became critical to engine survival. And the masters of this art were to be found at Bosch.

The first competition department to use Bosch Motronic engine management was BMW, which was putting its engines under enormous loads, both in IMSA sports-prototype racing and in Formula 1. This was a relatively primitive setup, with the ECU primarily concerned with managing the mechanical injection system, but very soon a complete system called MP1.2 was unveiled, which was developed initially with Ford for use with its stillborn Escort RS1700T Group B rally car.

Both Audi and Porsche seized upon the availability of the MP1.2 for their respective motor sport programmes in the FIA World Sportscar Championship and the FIA World Rally Championship. The MP1.2 could harmonise the amount of turbo boost required to the speed of the engine, read the water and intake air temperature, manage the fuel injectors and control the point of ignition. Initially it could only manage all of this if there was a single injector per cylinder, but this tended to make throttle response rather ponderous, compounding the pre-existing turbo lag.

When Bosch was able to upgrade the MP1T with two injectors per cylinder, the dreaded throttle lag was reduced back to the same level as it had been with a mechanical injection – but with far greater reliability and efficiency, meaning more power.

The final step was to fine-tune the boost levels and throttle response by means of the wastegate. Initially a larger capacity wastegate from the Porsche 930 was used, in order to maintain the speed of the turbines inside the turbocharger when the engine revs dropped by blowing surplus pressure outside the system. This effectively fooled the turbo into believing the engine was still pulling hard to ensure that the boost remained optimal when the driver got back on the power and reducing throttle lag.

The advent of the 20-valve engine meant that pressures were too high for the single wastegate to cope so a smaller second wastegate was taken from the Porsche 944 Turbo and plumbed in between the turbo and the intercooler, which was managed by the ECU. This second wastegate was plumbed in reverse and meant that it reduced the backwards pressure when the revs dropped, dumping the gases back in to the manifold to complete a second lap of the system.

This rather complex system was called Umluft and made its competition debut on the 10-valve engines at the Portugal Rally in 1984. It was Umluft that then gave the significant increase in the volume of whooshing and popping that the high-rewing 20-valve engine is famous for: as much a part of its soundtrack as the shrieking five-cylinder engine.

By the time that the Audi Sport quattro S1 appeared, the only way in which Audi could hope to make its front-engined car competitive against the bespoke mid-engined silhouette cars of Porsche, Lancia and the rest was to outgun them. This in turn reduced the system’s tolerances and made engine failure a much more common problem for Audi than it was for its rivals – but when these engines were on song they were mesmerising, and could not have been achieved without the remarkable little black boxes from Bosch.

Related Articles

Вашият коментар