Turbochargers have been around for quite some time. In production cars, they’ve existed since the late 1970s, bolstered by feats of small-engine turbos in F1 cars winning races ahead of naturally aspirated cars with more than twice the displacement. In Aussie racing legends, V6 turbos have given larger V8 muscle cars a run for their money.
Turbocharged engines are a common sight today, and feature in most car makes. The trend in cutting down on engine size means large naturally-aspirated engines are rapidly being replaced by smaller turbocharged engines. Emissions regulations are one thing supporting that trend, the other – rising fuel prices. Turbos use less fuel and emit less CO2 while achieving better performance figures than naturally-aspirated engines with the same power output. Initial hiccups, like ridiculously long turbo lag, and a tendency to break down have long been resolved by electronics, improved parts design and better materials.
How do Turbos work?
Turbos gain their power advantage by reusing exhaust gases. These are funnelled in through a turbine from the exhaust flange. The turbine spins at enormous speeds, enabling a compressor to spin and suck in vast amounts of air that is used in combustion. More air means more fuel and a bigger bang. To cool the air for combustion, making it denser in the process, an intercooler is used. This is a general take on things, but more complex parts, like wastegates, turbine shafts, strengthened inlet and outlet valves all play a part in delivering the right amount of air at the right time.
So, can a naturally aspirated engine be turned into a turbo? The short answer is yes. Car tuners are adding performance turbo systems to many of their favourite cars with naturally aspirated engines. The long answer is that you’ll need more than a turbine and compressor to achieve the expected gain in power. Because of the increase in pressure and power from the sudden burst of air, a whole host of modifications to the stock engine and transmission are needed.
Parts to Consider
I’ll lay out the general modifications you need to make to a naturally-aspirated engine. These are listed in random order.
- Replace the stock exhaust. Since there is increased air flow, your stock exhaust won’t be able to handle the pressure and heat. Larger, straighter piping with wider diameters helps. You can go for a cat-back exhaust, with new exhaust parts up to the catalytic converter. Or, for the best results, a turbo-back exhaust system would also mean reinforced exhaust manifolds and flanges.
- Upgrade the fuel pump and injectors. Since more air needs more fuel to burn, a fuel pump with greater capacity and uprated injectors will provide just enough fuel to achieve optimal combustion.
- Upgrade the stock clutch. More horsepower means more torque. To transfer all that power to the wheels by way of the transmission without slipping, your old clutch needs to give way to something with a bit more bite.
- Upgrade the engine internals. This is where things can get pricey. You need to get strengthened conrods and pistons, preferably forged aluminium for the pistons and steel alloys for the conrods. Kits of matching conrods and pistons are available for most engines. You also go the whole hog and replace the existing crankshaft to better accommodate the new pistons and conrods. Performance cranks are treated in nitride for added strength and longevity. Look for a lower compression setup to get the most turbo boost.
- Change the engine mapping in the Engine Control Unit. This might mean you need to replace your car’s stock ECU with another model that will adjust the timing and output of the injectors to match the increase in air intake. Alternatively, you can add a tuning chip to smooth things out.
Installing a turbo itself can be relatively straightforward, that is if you’re into car rebuilding and tuning. For the complete novice though this might prove daunting. Before installing the turbo, it is advised to change oil and air filters and the oil itself. For detailed instructions on fitting a performance turbo system, check out this video from one of the best-regarded turbo manufacturers.
Benefits of Turbos
Engines fitted with turbos offer a few advantages over their naturally aspirated siblings. Here are some of the basic plus points:
- Increased power and torque – With the tendency to go for smaller, lighter engines manufacturers need to make up for downsizing. Smaller engines today provide the same output figures both in bhp and Nm for horsepower and torque in engines of a decade ago but with twice the displacement. In addition, turbos have a notable place in diesels, particularly for low down torque when towing. All new diesels are turbocharged. Similarly, large non-turbo petrol engines can be modified to achieve even better results, with instant pickup of speed such as in big Aussie V6s and V8s.
- Fuel efficiency – smaller engines mean lighter cars. The less weight a car needs to pull around the less fuel it will need. Also, turbos engage relatively low in the rev range, typically between 1500-2500 rpm, meaning less fuel is wasted in building up speed. Turbo lag is minimised by complex electronics to get smooth, linear acceleration.
- Lower emissions – by using less fuel, turbocharged cars emit fewer toxic particles. Stringent environmental regulations have helped in this aspect.
Of course, most people modifying cars will be interested in the performance gains. If you’re rebuilding an Aussie classic or fitting a turbo to any car, packaged performance turbo systems are sold through car rebuilders and specialised retailers nationwide.