Having your cake and eating it - a bigger engine, tuned and with forced induction. well-known and respected engine tuning company expressed the dilemma as, horsepower sells engines, but torque wins races. The quote stands good in a road car context because torque makes for good acceleration and drivability. A peaky engine with lots of horsepower, but little torque, would be tiresome to drive on the road, other than on very long and fast straights. Having gone through the very basics of what engine tuning is about, this brief explanation will be referred to, and amplified by specific examples, throughout this chapter, and others. Coupled to our basic engine tuning theory, it is necessary to understand what units of measurement are used in respect of engine power outputs, and how to convert from one unit of measurement to another for purposes of comparison. ENGINE A section of a Rover V8 cylinder head reveals that the port is smaller in section around the valve guide (which is protruding). The faint pencil line indicates where the engine tuner would remove metal to improve gas flow. In the early days of motoring the car was known as the 'horseless carriage' and its power compared to that of the horse; the term 'horsepower' was coined, and has largely stuck ever since. However, there are American, British (or imperial), and metric units of horsepower, as well as other commonly used units of power measurement. Metric horsepower is usually abbreviated as PS, which is an abbreviation for Pferdestarke (the German word for horsepower). A single unit of horsepower (SAE) is equal to 1.0139 PS, 745.70 Watts or 0.7457 kilo Watts (kw). As far as torque is concerned, to convert from Nm to lb/in multiply by 8.851 and for lb/in to Nm multiply by 0.113 (remembering to convert the inches to feet to get the final answer when going from Nm to lb/ft). Time to start to plan what is to be done to the engine. The following list suggests an order of priority for making the key decisions - 1. Is torque or horsepower to be the This cutaway drawing of the Chevrolet Northstar V8 engine reveals all of the working components of an engine. (Courtesy - Chevrolet) 13
COOLING SYSTEMS brackets and my experience is that the fan to body mounting, in the form of adjustable bars, is the best. This type of fitting comes with two bars and, if you need a third, Kenlowe can supply it. Once fitted, the activation of the fan can be by a thermostatic switch, direct switch, or a combination of the two. Warning! - As many people have learned from the bitter experience of an underbonnet fire, you must always use a rubber grommet when passing a wire, or wires, through any part of the body. The Kenlowe, and probably most electric fans, can be made to run in either direction. However, because of the pitch of the fan blades only one direction is correct. With the Kenlowe, fans are either push or suction, so decide which side of the radiator the fan will be mounted before ordering. This illustration shows hot and cold air flows. (Courtesy - Kenlowe Ltd) A Kenlowe 11in fan kit. (Courtesy - Kenlowe Ltd) Another Kenlowe fan but in a larger size (13in) and showing all the components that come in a fitting kit. 65
SPEEDPRO SERIES Some dampers, as shown here, form part of a suspension strut. (Courtesy - Tenneco Automotive) Double wishbones with coil over shock absorber seen here on a Caterham 7. It is often easier to ensure that the spring and damper match by buying the components in a kit like this one from Whiteline Automotive. (Courtesy - Whiteline Automotive) just that it reduces roll, but that it only has a pronounced effect when the car does roll. This is unlike the affect of fitting stiffer springs which reduce roll but have a pronounced reaction to road bumps, even when travelling in a straight line. Once fitted, an anti-roll bar links both sides of the suspension on a single axle. Often, but not always, the anti-roll bar is additionally mounted at a central point on a subframe or chassis section. For vehicles that already have anti-roll bars fitted, it s often possible to further limit roll by increasing the thickness (diameter) of the bar. In addition to the use of a thicker bar, in some instances it s possible to have the rubber in the locating links (where used) replaced with a less compliant material like polyurethane. Ride height and spring stiffness must be set before selecting an antiroll bar. The reason for this is that the lower the front end of the car, and the stiffer the front suspension, the less weight transfer there will be, and therefore the less work for the anti-roll bar to do. Anti-roll bars are rated by thickness, which may be expressed in fractions of an imperial inch or in millimetres. Note, though, that just a few millimetres or sixteenths of an inch can double the stiffness of the bar so, when testing for the optimum bar size, only go up a size at a time. The reason for this is that stiffness increases as a fourth power of change in diameter. Put another way, you have to multiply the diameter four times to calculate a stiffness value. For imperial bars you will need to convert the diameter to the metric equivalent. As an example, a 22mm bar gives an end value of 234,256, while a 26mm bar has a value of 456,976 (i.e. 26 x 26 x 26 x 26). You can see then, that while the 104
WHEELS & TYRES The A008P from Yokohama. TYRE SPEED RATING Symbol MPH KPH L 75 120 M 81 130 N 87 140 P 93 150 Q 100 160 R 106 170 S 112 180 T 118 190 U 124 200 H 130 210 V 149 240 W 167 270 Y 186 300 The writing on the wall. There s a lot of information on the side of a tyre. (Courtesy - Michelin) be safe to run at that higher speed, whether or not you intend to use top speed. As an aside, be aware of the maximum permitted running speeds of space saver-type spare wheels. The accompanying table provides all the information you need. OVERALL SIZE When considering what size wheel and tyre combination to fit, there are a number of constraints, and therefore a number of decisions, which need to be made and planned for. The overriding constraint on overall diameter of Another choice of performance tyre is the Goodyear Eagle F1. (Courtesy - Goodyear Dunlop) 115
AERODYNAMIC DEVICES & BODYWORK smooth surfaces without the bumps, potholes and so forth found on the public highway. The key to understanding what aerodynamic devices are useful for the road is in the relationship between drag and downforce; the less drag a vehicle has, the higher its straight line top speed will be. For cornering, the limitation on the speed attainable will be down to the amount of grip available. If pressure, or more helpfully, downforce can be applied to the tyres more grip is achieved. An aerodynamic device can produce the required pressure, but at the expense of increasing drag. In racing, the trade-off between drag and downforce is balanced to produce the best package. Drag is usually split into separate categories, namely: 'form drag', 'lift drag', 'interference drag', and 'service drag'. Form drag is the drag created by the basic shape of the car. Lift drag is created by air that passes underneath the car and creates undesirable lift. Interference drag, also known as 'skin drag', is created by mirrors, trim, etc, and the surface of the car itself. Service drag is created by the passage of air through the car for cooling and ventilation purposes. So much for the bare basics, now it's time to take a brief look at what bits can do what. You should bear in mind, however, that we are looking purely at the theory here (a poorly designed product will achieve little or nothing, and many manufacturers do not test their products in a wind tunnel to see if they work or not). might be seen when a spoiler is fitted. At high cornering speeds a good front spoiler might also reduce front end lift and provide increased traction for the steered wheels and for the driven wheels of FWD cars. Rear spoiler A rear spoiler works by changing the way the air separates at the tail of the car and thereby reduces drag. However, unlike the front spoiler it is much easier to increase drag here than reduce it. As far as increasing downforce goes, most rear spoilers aren t going to make much difference on a road car. Aside from fitting spoilers, it is worth looking a step further and considering a whole kit of parts that comprise some or all of the above as well as changing the styling of the car (body or styling kits). BODYWORK KITS A great many bodywork or styling kits will change the overall look of the car, and ones that include properly developed spoilers may improve the overall performance of the car too. On the negative side, all bodywork kits add extra weight, and that s bad for performance. Most kits are styling, rather than performance, orientated - and you need to bear that in mind. As far as choosing a good kit instead of a bad one, you can ask if any information is available on the aerodynamic performance of various kits - but be prepared to be disappointed. ROLL BARS & ROLL CAGES For a soft top car (including removable hardtops) it is worth fitting roll hoops or the more motorsport orientated roll bar for safety reasons alone. If you want to fit a full roll cage to the bodyshell, either for safety or to increase torsional stiffness, the performance benefit will be in cornering where suspension geometry changes due to body flex will SPOILERS Front spoiler A decent front spoiler, or maybe a deeper front spoiler, can improve the coefficient of drag of your car. Depending on how good or bad the car is, speed improvements of 2-4mph A combination of body kits complete with a neat paint job can transorm your fast road car as shown here. (Courtesy - Wings West) 127