Schrick VSR Manifold
Ever wondered why Audi and VW spent time and money developing two different V6 motors of very similar displacement and horsepower and torque? One of the reasons was certainly that of the limited under-bonnet space on Golf. There was simply not enough space to fit a longitudinally mounted V6 engine in the bay.
Audi’s V6 engine actually produces more torque than VW’s VR6 because it has a dual-length inlet manifold. However, VR6 does not have to be left out! An aftermarket inlet manifold which does just the same thing is available from Schrick. VW’s accountants apparently kept the variable inlet manifold from standard production engine due to its high cost. Fitting the manifold would have negated any cost-savings from developing the VR6 with one head.
Background
Limited by the transverse mounting of the VR6 engine, there isn't much room for generous inlet manifold. In order to achieve a good compromise between maximum power output, and adequate torque for 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 ensure positive inlet pressure.
A standard 2.8 litre VR6 produces 174bhp and 172lb ft of torque and the 2.9 litre engine achieves 190bhp and 184lb ft. But this achievement wasn't enough to satisfy the Wolfsburg Developers. To produce more torque lower down in the rev range, the 6 cylinders needed to breathe even more freely. The idea of the variable inlet manifold was born and developed in parallel with the assistance of Pierburg, the carburettor specialists.
That this piece of motor technology was not condemned to the depths of the Wolfsburg catacombs is thanks to the interests of Volkswagen Motorsport. They quickly realised the potential in the aftermarket industry.
How it works
The VSR manifold can be fitted to both 2.8 and 2.9 litre engines. Eventhough the VSR achieves similar aims to Audi’s switching inlet manifold, the operating principle is different.
In the Audi engine, a long, narrow inlet tract achieves high torque at low revs and maximum power is achieved using a short, wide inlet tract. For the engine to feed through the appropriate channels, 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 inlet manifolds, with the necessary switching.
In contrast, two diverse technologies are applied in the VSR. It is designed so that at low engine speeds, resonance is used to improve cylinder-charging efficiency. At higher RPM, oscillation-tuned, individual, broad tracts are used. Switching from one to the other is achieved by single flap, also vacuum operated at 4000 RPM.
The tuned inlet tract operates by the low pressure caused between the throttle valve and the inlet valve, by suction of the descending piston. Through inertia of the air in the tract, the airflow tends to keep moving towards the inlet, even after its 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. Further during the same stroke, inlet pressure falls followed by high pressure but not before the inlet valve closes.
In order to achieve optimal control of the oscillation and reflection of the column of air in the inlet tract, it needs to be closely co-ordinated with valve timing, but this is not possible due to variation in the engine speed. Even at mid-range-rpm, the valve opening and they are out of synch. The second pressure wave arrives much too early before the inlet valve closes and a backflow reduces fuel efficiency.
Now to achieve high torque under these conditions, resonance-fuel is utilized. This is achieved by closing the connection flap between a small resonance chambers immediately before short inlet tracts above the inlet valves. These transforms the 6-cylinder engine into effectively two 3-cylinder engines with uniform firing times, which do not have overlapping inlet strokes. A resonance pulse of up to 6psi (0.4bar) above atmospheric is achieved, leading to remarkable fuel efficiency and torque increases.
On the road
The effect of the manifold is immediately apparent – you won’t need any test equipment! A new urge is sensed almost right from the idle. There is markedly better acceleration up to 4,000rpm, followed by a strong surge to the redline. The switchover of the flap is almost undetectable from inside the car.
The new low to mid-range power is particularly useful in the higher gears. The 50-70 sprints in fourth is reduced by almost a second! Fuel consumption is also improved, as higher revs don’t need to be used as much.
Copied from club vr6 hope they dont mind :oops:
