Advanced Motorsport Engineering

Andrew Livesey

• Publisher: Routledge
• Year: 2012
• ISBN:
  9781136077418
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Advanced Motorsport Engineering is an essential textbook for students on Motorsports Engineering courses and a handy reference those already working in the industry.The book covers advanced topics in motorsport such as diagnosing and rectifying faults in engines, chassis and transmission. Sections on composite materials and advanced engine management systems provide a complete coverage of level 3 courses. Each unit in the IMI and EAL syllabus is covered in full and illustrated with photos, diagrams and key learning points. The chapters can also be easily matched to the BTEC National course structure.Motorsport is not just about the spectacle of some of the world's most popular and famous sporting events - it also plays a crucial role in developing new techniques and technologies. Getting a qualification in motorsport could be the first step in a career in one of the most exciting and challenging sectors of high performance engineering.

Andrew Livesey is the Head of the School of Engineering at North West Kent College, UK

CHAPTER 1
Engine

Diagnose and Rectify Motorsport Vehicle Engine and Component Faults

This unit looks at the types of engines used in club level motorsport vehicles; it builds on the material covered in the Level 2 Motorsport Engineering book by the same author. It should be read in conjunction with the chapters on inspection, overhaul, and modification in this book.

IDENTIFICATION

Identification of the engine before working on it is very important. The VIN number will help identify the type, or classification, of the engine. The detail of the engine will be given in a separate engine number, the prefix will identify the engine type, and the serial number will identify the exact engine.

With motorsport engines the build may be completely different to standard, for this reason you should keep a log of the engine build, detailing all the components including part numbers, sizes, and any other variants.

ENGINE PERFORMANCE

The two common terms used in motorsport are:

Power – this is work done in unit time.

Torque – turning moment about a point.

For a deeper definition of these terms you need to start with work done. Work done is the amount of load carried multiplied by the distance travelled. The load is converted into force, the force needed to move the car for instance in Newtons (N). The distance is measured in metres. That is:

As we also express torque in Nm, so it is common to use the term joule (J).

RACER NOTE

Joule is a term for energy. 1 J = 1 Nm.

If we use a force of 10,000 N to take a dragster down a 200 m drag strip then we have exerted 2,000,000 Nm, or 2,000,000 J. We would say two mega joules (2 MJ). We would need to get this amount of energy out of the fuel that we were using.

The force is generated by the pressure of the burning gas on top of the piston multiplied by the area of the top of the piston. So the work done is mean (average) force of pushing the piston down the cylinder bore multiplied by the distance travelled.

Example

The work done during the power stroke of an engine where the stroke is 60 mm and the mean force is 5 kN

FIGURE 1.1
LOLA T70B V8 engine

RACER NOTE

The mathematical symbols are those found on your calculator or mobile phone, * is multiply and / is divide.

The same mean force is going to create the torque, this time we are going to use the crankshaft throw – this is half of the length of the stroke.

Example
Using the same engine

The work done by a torque for one revolution is the mean force multiplied by the circumference. The circumference is 2πr so

That is for one revolution, for any number of revolutions, where n is any number, the formula will be:

Example

Using the same engine of the previous examples
The work done in 1 minute at 6,000 rpm will be:

Power is, as we said, work done in unit time, which is:

The motorsport industry uses a number of different units and standards for power, from our calculations we can use Watts (W) and kilowatts (kW) and then convert.

RACER NOTE

1 kW = 1,000 W.

and

Example

Following on from our engine in the previous calculations and examples:

The term Horse Power (HP or hp) was derived by James Watt as the average power of a pit pony. These were small horses used to turn pulleys to draw water from Cornish tin mines (pits) before steam power became more popular. He equated the power of his steam engines to a number of these pit ponies. For our purposes 1 HP equals 33,000 ftlb/minute.

In French, horse power is cheval vapour (CV); in German it is Pferda Stracker (PS).

For conversion purposes 1 HP is equal to 746 W.

The two standards for measuring power are the SAE system (USA) and the DIN system (Continental Europe).

Volumetric efficiency – in other words the efficiency of the engine of getting in fuel and air to fill the cylinder. The fact that an engine has cylinders of 1 litre (61 cu in) does not mean that you are getting

FIGURE 1.2 JCB Diesel world land-speed record holder engine

that amount of air and fuel into the cylinders. The flow of gas is affected by a number of points, mainly:

• size, shape and number of valves
• valve timing
• size and shape of the inlet and exhaust ports
• shape and location of combustion chamber
• bore to stroke ratio
• engine speed
• type of induction tract – air filter, carburetter or throttle body, inlet manifold
• type of exhaust system – manifold, silencers, cat, and pipe layout.

The volumetric efficiency is calculated by measuring the amount of air entering the engine and finding this as a percentage of the actual volume of the engine. The formula is:

The air flow can be measured on the test dynamometer by using either an air flow meter on the inlet or calculating the air flow from the pressure drop across an orifice. You would normally do this over a set time period so that the air flow is calculated in litres per minute (cu in/minute or cu ft/minute).

A typical engine might have a volumetric efficiency of 80%, a well tuned naturally aspirated engine may have an efficiency of 100% or even 105% with throttle bodies and all the right manifolds. And because the turbocharger is pressurising the air into the cylinder, the figure will be over 130%.

The greater the amount of air that can be packed into the cylinder, the more power the engine is going to give out. The saying is, there aint no substitute for cubes. That is, the more cubic inches (litres) of air, the more power the engine will develop.

Thermal efficiency – from volumetric efficiency you saw that you need to get the engine efficient in getting the air (actually air and fuel) in to and out of the engine. That is one thing. Now when the air and fuel is in the engine it needs to be burnt efficiently to produce as much energy as possible to be turned into power and that conversion of burning gas into turning the crankshaft needs to be as efficient as possible to get the maximum power out of the engine.

The power output is easy to measure on a dynamometer, either as an engine in a test rig, or the complete vehicle on the rolling road.

RACER NOTE

Lots of drivers know the power output of their engines, very few know the efficiency of the same engine – greater efficiency means fewer refuelling stops and hence faster race times, in other words more wins.

To calculate the energy input you are going to need to know:

• Mass of air used – that is volume of air multiplied by the density. The density depends on altitude, temperature and weather conditions.
• Mass of fuel.
• Specific calorific value of the fuel – how much energy it produces for a given amount.

The calculation for the mass of air follows on from the measurements of air flow from the volumetric efficiency calculations. The calculations for density may be made by either sampling or using tables.

RACER NOTE

Many racing classes require the use of a control fuel – so all competitors are equal.

STP – Standard Temperature and Pressure

STP – Standard Temperature and Pressure – is defined as air at 0 °C (32 °F) and 1 bar (14.7 psi).

Also STP – commonly used in the Imperial and USA system of units – as air at 60 °F and 14.7 psi.

NTP – Normal Temperature and Pressure

NTP – Normal Temperature and Pressure – is defined as air at 20 °C (68 °F) and 1 bar (14.7 psi).

Air density at sea level at NTP is 1.2 kg/m³ (0.075 lb/ft³).

RACER NOTE

Have you ever noticed that on a cold, damp day the engine runs well and sounds well – this is because the air is at maximum density and the water cools the cylinder to prevent detonation.

The energy from fuel is discussed under fuel composition later in this chapter, examples of calculations can be found on the website.

RACER NOTE

Some simple changes, like chipping, may increase the power by 5% or 10% but increase fuel consumption by 40% – customers may have a shock at the increase in fuel costs.

Valve timing – is very important on a competition engine. The basic principles are to open the valves as quickly as possible, as great a distance as possible, and for as long as possible. The problem is that if you do this, the engine will need to run fast to maintain gas velocity, so it is likely to stall at low engine speeds, or at least produce low power. To this e...