Unit 25 Engine and Vehicle Design and Performance

Unit 25:

Engine and Vehicle Design and




Unit code:

QCF level:

Credit value:


This unit will develop learners’ knowledge of engine and vehicle design and will enable them to evaluate engine and vehicle performance.

Unit abstract

This unit will examine the aspects of design that relate to the function of engines, with a particular emphasis on performance. Learners will examine vehicle design for light and heavy vehicles with a view to understanding performance curves and other data used to evaluate vehicle performance. Learners will also appreciate possible future developments in vehicle engineering and in particular the use of new technologies, materials and design method.

Learners are introduced to engine design features, operating parameters and the likely effects when these are varied or altered. They then investigate engine performance and will analyse the data obtained from engine trials. Learners are introduced to the design features of light and heavy vehicles with particular emphasis on aerodynamics and transmission systems. They will then evaluate vehicle performance under different operating conditions and interpret vehicle performance curves.

Learning outcomes

On successful completion of this unit a learner will:

1       Understand engine design features

2     Be able to evaluate engine performance

3       Understand vehicle design features

4       Be able to evaluate vehicle performance.

Unit content

1      Understand engine design features

Engine design features: eg cylinder bore diameter, stroke length, con-rod to crank ratio, the number and arrangements of cylinders, overall engine dimensions, piston design, compression ratio, combustion chambers, camshaft design, crankshaft design, use of emerging technologies in engine design, new materials, alternate and multi fuel engine design (Electric, Compressed Natural Gas (CNG), Liquid Natural Gas (LNG), gasoline-electrical hybrid)

2      Be able to evaluate engine performance

Performance characteristics: torque; power; mechanical efficiency; thermal efficiency; volumetric efficiency; mean effective pressure; specific fuel consumption; emission control assessment

Engine performance mapping: graphical account of the role of map data; mapping procedure; visual interpretation of a fuel map and ignition map; fuel/ignition maps for different engine performance applications eg economy, power and torque

Performance curves: curves eg for spark ignition (SI), combustion ignition (CI) and pressure charged, rotary engines; engine test at various engine speeds; critical evaluation of air/fuel ratio; torque, power; exhaust emissions; fuel consumption; significance of the standards used to measure engine power eg BSAU, DIN, SAE, EEC; application of engine performance curves and design to the selection of appropriate power units for specific tasks

3      Understand vehicle design features

Features of vehicle design: light and heavy vehicles; body type; body shapes and design; aerodynamic devices; transmission; 5-speed; 6-speed; range change; splitter; four-wheel drive; multiple axles; chassis; laden weight; unladen weight; power to weight ratio; use and applications of new technologies, materials and design methods

4      Be able to evaluate vehicle performance

Performance monitoring: tractive effort; tractive resistance; air; rolling and gradient eg power available, power required

Performance characteristics: performance curves for different vehicles; tractive effort available for different combinations; tractive effort required for types of vehicle eg in laden, unladen conditions; acceleration possible with different combinations of engines; transmissions and vehicles; gradeability; the change in engine speed that results when changing from one gear ratio to another eg various gear ratios and transmission units; the effects of a change in engine speed produced by a gear change on engine torque, power and fuel consumption, the road speed of a vehicle

Vehicle performance curves: for selecting appropriate vehicles from data calculated

Air resistance: air resistance using the formula RA = K V2A; air resistance variation with engine speed and its effects on fuel economy; Cd, CdA, typical values for light and heavy vehicles; methods used to reduce air resistance of vehicles

Learning outcomes and assessment criteria

Learning outcomes
Assessment criteria for pass
On successful completion of
The learner can:
this unit a learner will:

LO1 Understand engine design
identify and discuss the engine design features that

contribute to the selection of an engine for a given


analyse the effects of altering engine design features for

a given application

LO2 Be able to evaluate engine
determine the performance characteristics of a given


carry out and record the outcomes of an engine

performance mapping procedure

interpret performance curves and select and justify the

use of an appropriate engine for a given application

LO3 Understand vehicle design
discuss the features of vehicle design that contribute to

the selection of a vehicle for a given application

analyse the effects of altering the features of vehicle

design for a given application

LO4 Be able to evaluate vehicle
explain the terms used in vehicle performance


determine the performance characteristics of a given


perform calculations to determine vehicle air resistance

and explain the effects of air resistance on engine speed

and fuel economy

interpret performance curves and select an appropriate

vehicle from given information.


This unit has links with Unit 74: Vehicle Fault Diagnosis, Unit 75: Vehicle Systems and Technology and Unit 79: Vehicle Electronics.

Essential requirements

Centres will need to provide access to suitable engine test facilities and manufacturers’ manuals and performance data.

Employer engagement and vocational contexts

Delivery would benefit from visits to motor industry test facilities for engines and/or vehicles and the attendance of guest speakers with experience of engine/vehicle design, testing or refurbishment.