| The Engine Volkswagen has announced details of an amazing 1.9 litre competition diesel engine which develops 170bhp yet is even more fuel efficient than the production TDI unit upon which it is based. Normally, attempts at extracting high power from a diesel engine are accompanied by visible smoke from the exhaust, but not in the case of this diesel. By paying close attention to the turbocharging and fuel injection system modifications, plus the retention of the diesel exhaust catalyst, the Volkswagen engineers have ensured that the motorsport engine produces no visible smoke. To put the achievement into perspective, this diesel engine produces only 4bhp less than Volkswagen's famous 2.7 litre VR6 petrol engine, the most powerful unit available in a production Golf. Torque is even more sensational at 300Nm, all the way between 2,000 and 3,900 rpm. This is 27 per cent more than the beefy VR6 develops which is rated at 235Nm at 4,200 rpm. All these benefits are achieved without the penalties of poor low speed torque and the tempramental running that are often the characteristics of spark-ignition motorsport engines. The Volkswagen "racing TDI" displays absolutely no temprament, pulling smoothly and very strongly from idle to maximum power. Fuel efficiency is slightly better than Volkswagen's benchmark production TDI. The modified unit uses just over one per cent less fuel for each of its 170 horses than the 110bhp production engine, the fuel efficiency champion of production cars. The Car Prepared in accordance with Group A regulations, the Golf TDI racer weighs 995 kilograms and is fitted with an 80 litre fuel tank. Due to its extrememly low diesel consumption, refuelling is required only once every four hours, saving valuable time of the track making the car well suited to the longer German motoring events for which Volkswagen Motorsport of Hannover has developed the car. Its potential was recently demonstrated before disbelieving eyes at the Nurburgring and at Spa , 24-hour races at which appeared two elegantly painted Volkswagen Golfs. Despite extremely short preparation times the cars were victorious in the diesel class in both races. Having overcome initial transmission problems, the cars moved closer to success in the overall ratings. Since Spa, modified six-speed racing gearboxes have been fitted. These are better matched to the engine power delivery characteristics. The diesel has now shown its efficiency under racing as well as road conditions, where similar spark-ignition engines consume approximately 50 per cent more fuel. To avoid speculation it must be stated that Volkswagen is not planning to make a roadgoing version of this racing car. For the engineers, however, such motorsport challenges are of extreme importance and represent a major source of motivation. This activity provides an opportunity to test and develop diesel engines under the toughest of conditions and to detect weaknesses which may not come to light in production models with lower output even at very high mileages. Production components used in the 125kW (170bhp) TDI engine did not reveal any weaknesses, so that further moderate increases in performance appear feasible. For the Technically Minded. Volkswagen development engineers based the high-performance power unit on the four-cylinder, 1.9 litre production engine. This is a direct injection and intercooled unit developing 110bhp at 4,150rpm and peak torque is 235Nm at 1,900rpm. The unit powers the VW 1.9L TDI road cars. Diesel engines have a lower maximum crankshaft speed than equivalent petrol engines as the combined fuel injection, ignition and combustion process takes longer. Attempts to run a diesel engine too fast result in reduced power, poor efficiency and higher emissions levels. For these reasons the maximum crankshaft speed is governed to 5,000rpm. The power and torque increases therefore had to be obtained by modifying the breathing and turbocharging and the fuel injection systems. Port cross-sections were enlarged to improve airflow and a larger Garrett turbocharger fitted. This retained the variable-geometry blade technology of the production version. In contrast to mormal tuning procedures for motorsport, Volkswagen did not wish to depart from the principles it applies to the development of production engines. In other words, the engine had to produce higher performance without creating any visible smoke, and retain the same specific fuel consumption level as its road going counterpart. Its components were rated to complete a 24-hour race reliability. The cylinder block, cylinder head and crankshaft were taken directly from the production line. Only the engine mountings and cylinder head ports were subject to modification. The camshaft and valves were also optimised, and the dual-mass flywheel used in the production version was replaced by a lighter, single-mass flywheel. The distributor-pattern injection pump was uprated in order to raise fuel delivery rates but the standard five-hole injector nozzles were retained but with holes of increased cross-section. Consequently, pre- injection now takes place at 250 bar pressure and main injection at 340 bar. As in the production version, fuel pressure at the nozzle peaks around 1,200 bar. A Bosch EDC 15 engine control unit with 16 bit microprocessor regulates injection and turbocharger boost pressure just as it does in the roadgoing car. Thanks to these individual measures, mean effective pressure has risen from 15.6 to 20 bar, a figure which underlines the engine's greater efficiency. As a result, minimum specific consumption has dropped from 197g/kWh to 194.6g/kWh, proving that high-performance engines can be even more fuel efficient than even a world beating production counterpart. This has a themal efficiency rating of 43 per cent! That is to say, it is capable of converting 43 per cent of the thermal energy in the fuel into mechanical energy. As far as Volkswagen is aware there is currently no production internal combustion engine in a passenger car that betters this figure. Maximum power output is now 125kW/170bhp, and is available between 4,000 and 4,300rpm. Peak torque is 300Nm, extending from 2,000 to 3,900rpm. Maximum boost pressure has risen from 1.95bar with the production engine to 2.53bar and maximum cylinder pressure climbs to 175bar, despite a reduction in the compression ratio from 19.5 to 18.5:1. Thanks to a larger radiator and charge-air intercooler, as well as a new oil-air type of oil cooler, the racing engine displays excellent thermal properties which can easily match any road going counterpart. In fact, there were never any temperature problems during races, despite the fact that the engines were constantly running at the limit. |
| THE TDi-R |