10 Jul 06
Using the 1.4-litre 89bhp FSI petrol engine as their starting point, VW's engineers set about boosting its power by a significant 78bhp, while at the same time maintaining durability and reliability. The engine block is made from cast iron and can cope with sustained cylinder pressures of over 300 Psi. The injectors have also been modified, with each having six output nozzles, allowing more fuel to be injected directly into the cylinder at higher engine speeds.
Here's how it works: the supercharger boosts torque and power at the lower end of the rev range - from 1,750 to 3,500rpm - with the turbo taking over at 3,500rpm and all the way to the 7,200rpm rev limit. This means that the TSI engine doesn't suffer from any turbo lag - the time before the turbo spins up to the point where it becomes effective at producing boost.
The turbo has air flowing through its turbine blades all of the time, whereas the supercharger only functions at lower revs. Once 3,500rpm is reached a bypass valve opens, which disables the supercharger. That's because at more than 3,500rpm the supercharger is an inefficient method of producing boost, because it needs to be mechanically spun to work. It does mean, though, that you don't have to wait for the boost to develop as it is more or less 'instant on'. By comparison, the turbocharger is driven by exhaust gas, hence the wait for it to 'spool up' as engine rpm increases.
To take the supercharger out of the equation once the engine is spinning quickly enough for the turbo to be on song, VW has employed a magnetic clutch within the water pump that engages the supercharger's drivebelt at 1,250rpm and disengages it once the bypass valve opens at 3,500rpm.
