Superchargers!

Why bother? Why not turbocharge? What did VW choose? [inc. photo] How does it work? [inc. photo] What goes wrong?

Why bother? Well you could just have a whopping great engine to get more power and parhaps more importantly torque. Generally a big engine has all sorts of packaging problems. Anything over 2.2 Litres and you really have to go to a six cylinder if you want smoothness. But a straight six is too long for a transverse application so you end up with a long bonnet.....and more importantly bad handling as it tends to understeer unless you do fancy things like having the gearbox and final drive as the rear axle aka. Porsche 944....

ok ok so I know smart arse VW solved this problem by having a staggered V6 engine but it still puts a lot of weight over the front axle.

When you look at your Mk1 or Mk2 golf the engine is set far back in the engine bay this aids turn in.

Why not turbocharge? Firstly lag...in order to get the turbo spinning from the exhaust gases you have to wait for the gases to speed up, hence you put your foot down and wait. Turbo's need low compression engines to stop pre-detonation so the response is sluggish then as the gaes get going all of a sudden whoosh. Also as there is a shaft connecting the turbo sections together it means that you need a larger intercooler to cool the petrol charge before it enters the cylinders.

What did VW choose? Vw chose supercharging as it is driven directly from the crankshaft it means there is no lag. As soon as the revs increase as does the charging effect. Also as there is no extra heat involved the coresponding intercooler is much smaller making a very neat installation.

Here is a photo of a Corrado intercooler. Note how small it is....er and how its stuffed down in front of the nearside front wheel. G60 Rallye golfs have an intercooler in tandem with the radiator full width. They say that the Rallye will make more power than the Corrado chipped and pullied as it has this larger intercooler.

How does it work?

Study the three photos....ok.....looking at the pencil drawing above...the main drive from the crankshaft drives the centre shaft. This drive also drives through a timing belt a secondary shaft. This wobbles the magnesium rotor in a figure of 8. This pumps through the air in a way similar to a 'wankel rotary' engine. From here it is sent to the intercooler because the affect on compression is to raise the temperature of the gas.[Pv=nRT]. Pressure x Volume=constant x Temperature. The intercooler sends the charge to the throttle but at this point there is a bypass pipe. There is a valve which works inversely to the throttle. So when cruising all the air is sent to the secondary chamber of the supercharger nulling its affect, thus giving a better fuel consumption. When the throttle is pressed hard the valve shuts allowing full boost to the chambers.

What goes wrong?

Well the timing belt could snap.....big damage but quite rare. A large particle is sucked in through a leak in the air filter or pipe....if it is larger than 0.5mm then it will bridge the gap between the rotor and housing.... More likely and most common as the rotor turns exactly the same rotation [figure 8] the seals slowly make grooves in the housing walls....eventually the seals snag in the grooves and pop out and get squashed between rotor and housing.....   All very very expensive!!!