Wayne Ward Catches up on the Latest Developments in Cylinder Head and Block Materials and Manufacture

Machining blocks from solid billets or forgings is becoming more popular. This is for the Chevrolet LS1 engine (Courtesy of Dart) Wayne Ward catches up on the latest developments in cylinder head and block materials and manufacture Caseeyond the basic mechanisms in any race engine, there reviewperhaps just a question of agreed meanings when talking here about are a number of critical ‘static’ components, of which blocks and not lower crankcases. Given also that the manufacturing cylinder heads and blocks are probably the most important techniques used to make structural lower crankcases are very much structurally. Even where the engine isn’t solidly mounted, the same as those used for the cylinder block or upper crankcase, Band chassis loads aren’t transferred directly into and through these much of this article will apply to lower crankcases as well. components, they have to react to any loads due to engine vibration Taking this blurring of the boundaries between the major structural and car acceleration through the engine mounts. static casings a step further, there are engines in which the cylinder In production engines developed for racing, as well as bespoke race block and head are a single component. Such construction is engines, the structural integrity of these parts is critical to the success relatively specialised and expensive, and is thus only rarely seen. of the engine in competition. Materials and production methods are However, having the cylinder head integral with the block removes developing continuously, and this allows us to improve the reliability the need to seal the head-block interface – a source of many of our engines without having to cope with large increases in mass. problems for a wide range of engines, especially as they become Not only do better production methods help us make (or indeed more efficient, with supercharged/turbocharged engines representing purchase) cylinder heads and blocks that are likely to last longer for a particular challenge here. a given level of service stress, they can also produce the same part In the case of cylinder blocks, a growing number of race engines at a lower cost, or allow us to introduce more complex machining use linerless blocks. Whether this is the result of adopting a linerless operations without incurring too much extra cost. production engine as the basis for a racing powertrain, or the design of Given that, in many cases, blocks are extended way past the crank a bespoke linerless block based on technical considerations, this type axis, and the lower crankcase is formed by a simple closing plate, it is of cylinder block structure has a strong following. 30 FOCUS : HEADS AND BLOCKS Materials The range of materials from which large structural parts can be made continues to evolve, and as manufacturing methods change, so the material choices differ. With the huge growth in CNC machining and improved tooling, the manufacture of certain cylinder blocks is certainly possible, and billet-machining of aluminium blocks is popular for the manufacture of large drag race engines. The material choices are no longer driven by casting considerations, and a whole new range of materials is available. In general, wrought materials typically have higher strength than cast materials, and have fewer defects. Through the ‘hand-me-down’ relationship we have with the defence and aerospace industries, new materials often find their way into motorsport, and in the future we are likely to see the use of aluminium materials with much improved tensile and fatigue properties compared to the materials in common use today. Pouring CGI (Compacted Graphite Iron) NASCAR blocks utilising When it comes to using wrought materials in cylinder blocks, we SinterCast control system. (Courtesy of Grainger and Worrall) are really only going to be looking at aluminium alloys. While it is clearly possible to make blocks from all kinds of materials, billet iron or steel blocks are not likely to be cost-effective. The mass of suitable types of material have enjoyed significant development in recent years. billets for iron or steel blocks would be prohibitive, as would the The development of alloys based on existing aerospace aluminium expense of machining, given the reduced material removal rates for casting alloys has recently given us materials with greatly improved these materials compared to aluminium. In the past, fabricated steel fatigue properties compared to traditional alloys. For many years blocks have been used for engines; TVR notably used this technique of now, the favoured range of aluminium castings alloys have been the welding cylinder blocks for some of its engines. A35x materials. These have offered a good combination of properties Commonly, billet aluminium components for use at moderate and good ‘castability’, and remain the most common choice for temperatures are going to be made from an alloy chosen from the high-quality race castings. These alloys, based on aluminium alloyed 2000- or 6000-series materials. Of these, 6000-type alloys are good with silicon and magnesium (plus much smaller proportions of other enough for most applications and are generally less expensive than elements) or similar equivalents have typically taken up most of the 2000-series materials. Allan’s article (1) highlights the use of ‘billet racing casting market, from the keen amateur right up to Formula One machined’ heads and blocks for Top Fuel engines. Typically, it would and its huge development budgets. be difficult to make a cylinder head for a ‘conventional’ race engine However, in the past few years, the attention of a number of top from solid billet, owing to the need for cooling passages. foundries has turned to improving the casting behaviour of the Engines burning nitromethane for short periods don’t need cooling, A20x alloys originally developed for aerospace use. They represent however, despite their prodigious power output, so the heads and a step-change in the capability of materials to handle high stresses, blocks lend themselves particularly well to the billet-machined route. and we can expect to see their use increase markedly in the coming t Allan specifically mentions aluminium alloys 6061 for the block and 6013 for the head. Even where there is greater complexity required from blocks and heads, such as those that do require cooling, if you are prepared to accept some compromises then it can be possible to produce billet components, especially if you are prepared to accept assemblies with split lines, seals and joints replacing what were previously ‘solid’ castings. The choice of materials from which to cast heads and blocks is extensive. Often the rules of a series will narrow down the choice for us somewhat. For example, Formula One specifies aluminium, while NASCAR specifies that blocks This very compact V8 race engine uses production- are made from cast iron. Aluminium and cast based motorcycle heads on a bespoke cast iron represent the vast majority of materials from aluminium block (Courtesy of Radical Sportscars) which structural castings are made, and both 31 FOCUS : HEADS AND BLOCKS production of castings of greater complexity and with thinner walls. Cast-iron materials have not only enjoyed a protected market in some motorsport series, they have also enjoyed something of a resurgence in popularity in road vehicles too, particularly for diesel applications, from passenger cars to large commercial vehicles. CGI in particular has taken a large percentage of market share from engines traditionally made with grey cast iron blocks. One reason for this, besides the mass savings available from using a stronger material, is that CGI is stiffer. For racing this offers not only improved torsional and bending stiffness of the engine, but possibly lower friction as well. With lower bore distortion seen in service for the stiffer CGI blocks, piston ring point loading is reduced and lower tension rings can be used, both leading to lower friction. Outside of NASCAR, either currently or in the relatively recent past, CGI has been used in World Rally, DTM and Grand Prix motorcycle road racing. While Rally and DTM are series based on production engines, the 500 cc V4 two-stroke engine which reportedly used CGI for its crankcases had no such production-based limitations. The Toyota RVX09 V8 Formula One engine block is cast aluminium, as mandated by the series’ rules. It is linerless and runs less than 10 mm between adjacent bores. Here it is shown Owing to its high strength, cast iron replaces aluminium in line-bored with the sump (note integral pump housing) certain applications where it is simply not possible to put enough material in critical areas of an aluminium casting to prevent failure. years. They offer improved fatigue properties, especially at room A genuine advantage of cast iron over aluminium, in terms of day-to- temperature, compared to a material such as A357 (2). day component longevity, concerns linerless blocks. NASCAR Sprint These A20x alloys have significant additions of copper and, in terms Cup blocks can be used for up to 30 builds before then going on to of chemistry, can be compared to the 2000 series of wrought alloys. Nationwide competition, where they may be built a further 20 times There is some crossover between aerospace and motorsport in some of with only occasional minor re-boring and honing. While this requires the foundries in which motorsport castings are produced. Therefore, in an increased inventory of parts to cope with the effects of re-boring the some cases, there is prior knowledge of these new materials, and the cylinders, it represents an economical way of going racing with high- development of the material and its casting processes have not had to power engines. wait for a specific motorsport project to come along. It should be said Magnesium falls into a strange netherworld where race engines though that motorsport has sometimes been a driver for the adoption are concerned.

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