Getting more out of an engine
Performance tuning, according to Wikipedia, is generally restricted to cars required for motorsport, although the website also points out that many of these vehicles never hit the track, or are even driven “in anger” – and you’ll see lots of cars just like this if you visit the CRC Speedshow in July.
We’re constantly amazed when we go to the Speedshow to see how much love, attention, and money goes into these “show ponies”, and especially the high degree of engineering expertise.
The choice of modification depends greatly on the degree of performance enhancement desired, budget, and the characteristics of the engine to be modified.
Intake, exhaust, and chip upgrades are usually among the first modifications made as they are the cheapest, and make reasonably general improvements, whereas a different camshaft, for instance, requires trading off smoothness at low engine speeds for improvements at high engine speeds.
In the motorsport context power output, torque, and responsiveness of the engine are of premium importance, together with reliability and fuel efficiency, but for the “show ponies” responsiveness, reliability and fuel economy are often not relevant as the engines will rarely be taken to their maximum for the extended periods required in racing, rallying or other forms of motorsport.
One thing that’s sometimes forgotten when a client wants more power from an engine is that producing more power usually puts additional stress on other parts of the car, such as the transmission, driveshaft and any other load-transmitting powertrain components, and these will most likely need to be modified to withstand the load from the increased power.
Many well-tried and tested techniques have been devised to achieve more power, but all essentially operate to increase the rate (and to a lesser extent efficiency) of combustion in a given engine.
This is achieved by putting more air/ fuel mixture into the engine, increasing compression ratio (requires higher octane petrol) burning it more rapidly, and getting rid of the waste products more rapidly. Since getting more power – and using it – will mean more fuel is used, this also has to be factored into the equation as extra fuel may need to be carried, which will increase the weight of the vehicle and thus reduce its power to weight ratio.
In other words, the performance tuning of an engine should take place in the context of the development of the overall vehicle.
Now let’s have a closer look at ways to increase power. These include increasing the engine displacement by one or both of two methods: “boring” – increasing the diameter of the cylinders and pistons, or by “stroking” – using a crankshaft with a greater throw.
On older engines, using larger or multiple carburettors creates a more controllable air/fuel mixture to burn, and to get it into the engine more smoothly. In modern engines, fuel injection is more often used, and may be modified in a similar manner.
Increasing the size of the poppet valves in the engine, and thus decreasing the restriction in the path of the fuel-air mixture entering, and the exhaust gases leaving the cylinder, also produces good results, while using multiple valves per cylinder results in the same effect, although it is often more difficult to fit several small valves than to have larger single valves due to the valve gear required.
Using larger bored, smoother, less contorted inlet manifold and exhaust manifolds helps maintain the velocity of gases. Similarly, the ports in the cylinder head can be enlarged and smoothed to match.
This is termed cylinder head porting,