Limited by the transverse mounting of the engine, there isn't much room for generous inlet manifolding. In order to achieve a good compromise between maximum power output, and adequate torque in day to day use, the inlet manifold runs across the top of the head. This has circumvented the shortage of space and allowed the use of an oscillating-flow tuned inlet manifold. Each cylinder has its own inlet tract that is tuned to such a length as to en- sure positive inlet pressure. As engine output is proportional to the airflow, this scheme means that the VR6 doesn't have to be ashamed in the face of competitors. The 2.8 litre produces 174 PS [ DIN hp] and a maximum torque of 240 Nm at 4200 RPM, and the 2.9 litre engine in the Corrado achieves 245 Nm at the same engine speed. But this achievement wasn't enough to satisfy the Wolfsburg developers. To achieve even more torque, lower down in the rev range, the 6 cylinders were to breathe even more freely. The idea of the variable inlet manifold [ german "variables Saugrohr" ] was born and developed in parallel with the now standard version, with assistance from the Pierburg GmbH in Neuss, a company which has a high reputation with things relating to mixture control. The VSR [ abbreviated from the german ] system did not go into, falling victim to the red pens of accountants shortly before the VR6 started production. That this piece of motor technology was not condemned to the depths of the Wolfsburg catacombs, is thanks to the interests of Volkswagen Motorsport, based in Hannover. This VW company took the VSR and now offers it as an after-market conversion kit for 2888 Marks. The kit may be fitted to all VR6s with 2.8 and 2.9 litre engines.
Even though the VSR achieves similar aims to those of the switch- ing inlet manifold of the 2.8 litre V6s from Audi, the operating principle is different. In the Audi engine, a long, narrow inlet tract achieves high torque at low revs; 245 Nm at 3000 RPM. The maximum power is achieved using a short, wide inlet tract, pro- ducing 174 PS at 5500 RPM. For the engine to be fed through the appropriate channels, depending on engine speed, inlet manifolds are switched using six individual, vacuum operated flaps at 4000 RPM. In both stages, the technology is based purely on tuned oscillating-flow in- let manifolds, with the necessary switching.
The VSR in contrast, two diverse technologies are applied. It is designed so that at low engine speeds, resonance is used to im- prove cylinder charging efficiency -- at higher RPM, oscillation- tuned, individual, broad tracts are used. Switching from one to the other is achived by a single flap, also vaccuum operated at 4000 RPM. The tuned inlet tract operates by the low pressure caused between the throttle valve and the inlet valve, by the suction of the descending piston, Through inertia of the air in the tract, the airflow tends to keep moving towards the inlet, even after it's closed, causing a slight over-pressure when the inlet valve next opens. This ensures high charge efficiency even during early stages of the induction stroke. Of course, further during the same stroke, inlet pressure falls followed by a high pressure but not before the inlet valve closes.
In order to achieve optimal control of the oscillation and re- flection of the column of air in the inlet tract, it needs to be closely coordinated with valve timing, but this is not possible due to variation in engine speed. Even at mid-range-rpm, the valve opening and the are out of synch. The second pressure wave arrives much too early before the inlet valve closes and a back- flow reduces fill efficiency. Now to achieve high torque under these conditions, resonance-fill is utilised. This is done by closing the connection flap between a small resonance chamber which is immediately before short inlet tracts above the inlet valves. This transforms the 6 cylinder ending into effectively two 3 cylinder engines with uniform firing times, and which do not have overlapping inlet strokes. Resonance pulses of up to 0.4 bar [approx 6 psi] above atmospheric are achieved, leading to remarkable fill efficiency and torque increases.
Even though fitting the VSR requires not great skills, it should be undertaken by a professional with the right tools. For exam- ple, fitting the new EPROM and the new control harness requires dexterity and special tools. The new chip doesn't alter the previously-programmed behaviour of the engine management, it only adds an additional control output for the electrically- controlled, vacuum operated flap. The kit includes instructions as to complete installion, including connections to the vaccum circuit and electrical connections.
[ photos of chip in engine maganement unit, VSR inlet manifold being fitted, and side-by-side VSR with original manifold. ]Further engine modifications are not required, so one is permit- ted to anticipate the VSR transformation. A marked improvement in torque at mid-range is advertised with 255 Nm available at 3600 RPM on the 2.8 litre engine. This corresponds to an 11% increase at that engine speed. In the 2.9 litre incarnation, 260 Nm is available, providing more performance in the most-used rev range. There is no promise of more power in the higher RPM range.
To illustrate the performance improvement in a VSR Golf, one doesn't need any test equipment! Almost right from the start, at below 3000 RPM, a new urge is sensed. Up to 4000 RPM the engine provides markedly better acceleration, yet above, the previously expected manners appear because the torque curve corresponds to that of the standard engine. Even more! After the impetuous ac- celeration, the switchover feels almost reserved. The steeply in- creasing torque curve up to 3600 RPM also shows a rapid fall back to the norm between 3600 and 4000 RPM. The torque improvement is an excellent fit to the Golf VR6.
In fourth gear, the torque boost corresponds to 90 to 120 kmh, in fifth to 110 to 150 kmh. This turns the Golf into a sprinter, that none of the near-200 PS professionally tuned chariots comes near. Testign showed that acceleration from 90 to 120 kmh in fourth gear only took 5.4 seconds. The standard VR6 Golf took 6.1 seconds and a near-200 PS Oettinger VR6 Golf taking 6.4 seconds, and a Wendland special taking 6.2 seconds. No wonder be- cause their maximum torque happens at much higher RPM.
Unremarkably, the VSR trick didn't improve peak acceleration or top speed, both of these being exclusively in the higher rev range.
The VR6 opens up a new field for Volkswagen Motorsport tuning. This is appropriate when one expects high torque for comfortable and sporty driving. It's even more attractive because testing showed reduced fuel consumption by half a litre [ per 100 km ]. On the other hand, the VSR offers professional tuners an innova- tive platform for development - as some of them have already in- dicated.
| Suggestions related to the web site should be sent to the webmaster. Copyright © 1998 CCA |