The engines on these cars are basically the standard engines for that make and model but with turbo chargers bolted on to give more power! The RS Turbo and R5 GTT feature the Garrett T3 turbo charger, with the Fiat sporting a turbo made by IHI of Japan.
RS Turbo Engine on Left/above, Renault 5 GT Turbo Engine in middle, Fiat Punto GT engine on Right/below.
Simple explanation of a Turbo charger
A Turbo charger is just like a powerful hairdryer which blows more air into an engine so it can produce more power.
The turbo is just a pair of fans connected together. One (called the turbine or hot fan) is powered by the exhaust gas coming out of the engine (red arrows on diagram show exhaust gas) which spins the other fan (the compressor or cold fan) to push more fresh air into the engine (blue arrows in picture show air being pumped back into engine). Because all engines explode fuel to create power, they produce much more hot exhaust gas, than the amount of cold air they needed to suck in, and it is this fact which allows turbochargers to work.
How an engine produces power
All engines burn fuel with air to produce power, to get more power you need more fuel, and therefore more air to burn it with (trying to squirt in more fuel on its own cannot burn, so produces no more power, and just comes out of the exhaust pipe as smoke). See above the animated diagram of how an engine works - click diagram for more details.
The simplest way to get more power is to build a bigger engine - in simple terms a 1 litre engine will suck in 1 litre of air per cycle (which some fuel is squirted into and exploded by a spark to produce power), so to get more power you could just use a 2 litre engine, which can suck in twice as much air/fuel and produce roughly twice as much power every times it turns round ! Obviously the bigger engine will also be heavier, and use more fuel though.
What if I don't want a bigger engine ?
A non-turbo engine has to suck its full capacity of air in through fairly small valve in each cylinder every cycle , the faster the engine spins, the quicker it has to suck in this air it needs, as the engine is going twice as fast, the valves can only open for half the time, and it is this unavoidable problem which restricts the amount of air you can suck into a standard engine, and therefore the amount of power you can get out of a normal engine.At full power a Ferrari 360 3.6Litre engine consumes 60 gallons of air every second to generate around 400bhp (111bhp/Litre), and a 2005 3Litre Formula 1 engine consumes twice that to produce 900bhp (300bhp/Litre) - these are currently the limits of engine power possible for road/race cars without turbo or supercharging !
A turbo charged engine however can easily be around 40% more powerful simply because air is being forcibly pushed into the engine by the turbocharger, so the engine can consume more air without any other changes (other than more fuel being required), and can therefore produce more power.
With a turbocharger fitted, you can also increase the pressure of the air pushed in (the boost pressure often measured in psi) to get even more power, and so the power output is only really limited by the size of the turbocharger and the strength of the engine. Formula 1 engines were allowed to be turbocharged until 1988, and by then the tiny V6 1500cc engines such as the Cosworth engine shown below could produce 1500bhp (1000bhp/Liter) but they would only last for a few laps before they would self-destruct - which was enough to get a good qualifying position.
Road car turbochargers normally run at 10-20psi maximum boost pressure, providing up to 160bhp/Liter (2004 Subaru Impreza STi WR1 1994cc 320bhp). Increasing boost pressure above this things get a lot more complicated, as the strain on every part in the engine becomes enormous, so it becomes impossible to make an engine which is reliable enough for a manufacturer to provide warranty repairs, and can manage acceptable service intervals.
So why not just use bigger engines and forget about Turbo chargers
The big advantage of a turbo charged engine is that when the engine is idling, or driving slowly in traffic, the turbo will not be spinning fast enough to do anything, so you get the advantages of a small engine, with its low weight, good fuel economy, low noise and smooth running.When you want to accelerate hard and the turbo spins up, you get the power you want (and burn more fuel to get it), but only while you want it - a bigger engine would be heavier and noisier and would always use more fuel - even when idling or trundling along in traffic!
Another advantage is that bigger engines are generally less efficient, as the air flowing into a bigger cylinder is moving more slowly, so it doesn't mix with fuel as evenly, so some of the fuel is wasted by inefficient combustion - the turbocharged engine has faster air flow into the cyclinder (as it is pushed in by the turbo) so the air/fuel mix is more even, and the engine actually burns all the fuel rapidly, giving better power, and cleaner running.
Early in the 1990s Saab UK carried out an emissions test with a Saab 9000 Eco turbo in London city centre. They were able to show that the air from the cars exhaust was actually cleaner than the polluted air being sucked in by the engine - this was partly due to the efficiency of a turbocharged engine !
Whats the disadvantage of Turbocharging then
Turbochargers are kept as small as possible so they can spin up quickly and give minimal delay before power kicks in (called turbo lag). To get as much power as possible to spin the turbine (turbos spin at 100,000 rpm or higher) the turbocharger also has to be as close to the hot exhaust outlet as possible. This means the turbo gets incredibly hot - when the engine is flat out, the metal of the turbocharger body will get so hot it glows red as shown below !
Turbochargers have to be made to very tight tolerances which is what makes them expensive, but this also means as they start to wear, the tolerances go out of the window, and the turbo then deteriorates rapidly, often leaking oil which causes smoke from the car exhaust under load.
In order to spin this fast, the turbocharger spins in a bearing of liquid oil, so they require high quality clean oil all the time they are running, so require more frequent and expensive servicing than non-turbo cars, and if an oil change is left too long, or oil level is allowed to drop, the turbo can be damaged in a short time, and will then have to be replaced.
Lastly, turbocharged cars give most power at high revs when the engine is under its highest loadings, so the drivers of these cars are encouraged to drive the cars hard to get the amazing performance. This means the entire engine and drivetrain is also given a lot more abuse - this is probably why turbo cars have a reputation for being expensive to run, its because they get driven hard more of the time, so all parts get worn out more quickly (ie clutch, gearbox, brakes, suspension, tyres, and due to load on the engine and heat that generates - head gaskets are common failures).